Patent Publication Number: US-11649650-B2

Title: Compact universal gas pool heater and associated methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of, and claims the benefit of priority to, U.S. patent application Ser. No. 16/522,362 filed on Jul. 25, 2019, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/703,270 filed on Jul. 25, 2018, the entire disclosures of which are both expressly incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a compact universal gas pool heater and associated methods and, in particular, to a compact universal gas pool heater that has enhanced adaptability to various installation requirements, enhanced serviceability, and optimized heat transfer capabilities. 
     BACKGROUND 
     Swimming pools and spas use various types of heaters for heating the fluid being circulated in the pool or spa. For example, one common type of heater is a gas heater that often implements a water tube heat exchanger. The water tube heat exchanger is generally positioned proximate a source of heat, e.g., a burner, that is ignited by an igniter, which may be a hot-surface igniter, spark igniter, pilot igniter, or a combination thereof. In many gas heaters, the burner and igniter, along with a flame sensor, will be mounted to the same panel in order to maintain constant dimensional relationship between the igniter and the burner to ensure constant ignition of gas by the igniter. If these components were to be mounted on separate panels, then dimensional tolerances could potentially “stack up” and negatively affect the dimensional consistency. If this dimensional relationship were not maintained, then the potential exists for too much gas to be dissipated by the burner prior to ignition, which can result in a louder than normal ignition. 
     Furthermore, water tube heat exchangers generally include one or more tubes through which pool or spa water to be heated is circulated. The tubes are positioned such that hot gases generated by the source of heat pass across the tubes. The tubes absorb heat from the hot gases and transfer the heat to the fluid flowing therethrough. Metal fins can be secured to the exterior of the tubes to maximize the exterior surface area exposed to the hot gases and increase the efficiency of heat transfer. The heat exchanger can be positioned within a combustion chamber canister, which itself, and in combination with the heat exchanger, can be placed in a cabinet to prevent individuals from touching the hot canister and to protect the canister and heat exchanger from the elements. Gas heaters may also have electrical components that are powered by both high-voltage wiring and low-voltage wiring. These wires will generally have to be routed to the interior of the cabinet. Furthermore, gas heaters can also have a user interface that allows a user to control and program the gas heater. The user interface can be accessible from the exterior of the gas heater. 
     Gas heaters for swimming pools have particular installation requirements to which an installer must adhere, such as national, state, or local codes. Included in these requirements is that the gas heater cannot raise the temperature of nearby structures a certain number of degrees above the ambient temperature. To ensure that the gas heater does not increase the temperature of nearby structures, e.g., walls, fences, etc., too much, installers will space the gas heater away from such structures, thus providing a clearance between the gas heater and the structure. To determine the minimum allowable clearance for a particular heater, pool heater manufacturers will often test their gas heaters by measuring the temperature on nearby structures during use. Pool heaters typically have minimum clearances of 6-18 inches. In addition to maintaining a suitably low temperature on nearby structures, the clearance allows for a service technician to access the portion of the pool heater cabinet that faces the structure in order to repair the pool heater. However, the required clearance essentially results in an increase in the overall footprint of the pool heater since one must account for the required clearance. This is undesirable since space is at a premium when installing a pool heater. As such, it is not only desirable to reduce the minimum clearance, but also to construct pool heaters as small as possible so that they weigh less and fit into smaller spaces. 
     Furthermore, to provide adaptability to the various challenges that may be present in a pool heater installation site, prior art pool heaters generally allow an installer to configure the heat exchanger of the pool heater so that the water inlet and outlet is on one of two sides that are opposite one another (e.g., 180° apart). Additionally, prior art pool heaters allow the installer to rotate the entire cabinet top panel to two or three possible positions, which effectively moves the user interface panel to a more accessible/convenient location. However, each of these methods requires a significant amount of effort that involves removing entire panels and/or the heat exchanger, and reinstalling them in a different configuration, which is not only cumbersome but also time consuming. 
     Pool heater installers also have to tackle wiring issues that may arise. As referenced above, pool heaters require electrical power to operate, which will often be 120V or 240V AC delivered through high-voltage wiring, for example. In some cases, pool heaters will also be connected to a pool/spa automation system via low-voltage wiring. It is required by code that the high-voltage wiring be separated from the low-voltage wiring. Typically, to adhere to these requirements and codes, electrical wiring will be routed through a conduit, which requires the installer to install a conduit fitting into a hole that extends into the pool heater. Installation in this fashion can be difficult for installers since they will have to pull stiff wires through the conduit and fitting into a junction box. 
     In addition to the above, pool heater installers may remove an old pool heater and replace it with a new one for an existing swimming pool needing a new pool heater. In such circumstances, the installer may be motivated to install a new pool heater from the same manufacturer of the old pool heater being replaced, or in some instances the same exact model pool heater that was previously installed. This is typically because the replacement is most likely to fit in the available space, and have the same water connection position and fittings. However, this limits the number of options available and could influence the pool owner away from buying the pool heater they actually desire with the functionalities they need. On the other hand, if the pool owner were to opt for a different pool heater, then they may have to replace all of the water connections, which would result in increased costs. 
     Not only are installers faced with issues in connection with pool heaters, but technicians that service pool heaters also have their own troubles they deal with. While servicing a pool heater, a technician often has to access the pool heater components and electronics through the top panel. This generally involves removing the entire top panel completely. However, electrical wiring will often run from components of the pool heater to the user interface in the top panel, which means that when the top panel is removed for service it cannot be placed very far away. Thus leaving the technician looking for a place where they can temporarily store the top panel during service that is nearby, but not in the way. 
     One such component that a pool heater technician may have to replace is the solenoid gas valve that controls the flow of gas into the combustion chamber. In prior art pool heaters, the gas valve is often attached using threaded pipe fittings. However, this method of attachment makes replacement of the gas valve difficult, tedious, and time consuming. 
     Thus, a need exists for a gas heater that allows for enhanced adaptability to various installation requirements, enhanced serviceability, and optimized heat transfer capabilities. These and other needs are addressed by the compact universal gas pool heater and associated methods of the present disclosure. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with embodiments of the present disclosure, an exemplary gas heater is provided that includes a cabinet, a combustion chamber canister, an exhaust pipe, a heat exchanger, a burner, an igniter, and a water header manifold. The cabinet can include a first side panel, a second side panel, an exhaust side panel, a water header side panel, a bottom, and a top. The water header manifold can be positioned at the water header side panel and can be in fluidic communication with the heat exchanger such that it routes water through the heat exchanger. The heat exchanger includes at least one tube having a tube inlet and a tube outlet and can define a combustion chamber. The heat exchanger can be positioned within the combustion chamber canister and can be configured to extract heat from hot gases within the combustion chamber. In this regard, the burner can be positioned within the combustion chamber canister and the combustion chamber, and receive combustible gas from a combustion blower. The burner can dissipate the combustible gas, which can be ignited by the igniter. Gases can be discharged through the exhaust, which can be connected to the combustion chamber canister and extend through the exhaust side panel. The combustion chamber canister, the tube sheet, the heat exchanger, and the burner can be positioned within the cabinet such that the combustion chamber canister is spaced apart from the first side panel by a first gap having a first width, and is spaced apart from the second side panel by a second gap having a second width. The first and second gaps can be configured to minimize the transfer of heat from the combustion chamber canister to the first and second side panels, and prevent the first and second side panels from increasing in temperature more than a predetermined amount above the ambient temperature. The cabinet can be configured such that it can be installed with the first side panel or the second panel adjacent a structure with a clearance of six inches or less. 
     In some embodiments, the water header side panel and/or the exhaust side panel can include lower and upper vent openings. The lower and upper vent openings can circulate air through the first and second gaps, and lower the temperature in the cabinet. For example, the lower and upper vent openings can allow natural convection to circulate the air through the first and second gaps. The gas heater can be configured so that servicing can be performed through the top and water header side panel of the cabinet. The gas heater can also include insulation provided in the first and second gaps. 
     In other embodiments of the present disclosure, the cabinet of the gas heater can include a user interface module having a user interface, and the top can include a first lateral side, a second lateral side, and a channel extending between the first and second lateral sides that the user interface module can be removably positioned within. The user interface module can be removed from the top and positioned within the channel in a first orientation where it is accessible by a user from the first side of the cabinet, and in a second orientation where it is accessible by a user from a second side of the cabinet. 
     In some aspects, the channel can include first and second engagement mechanisms, and the user interface module can include a user interface engagement mechanism configured to engage the first and second engagement mechanisms. The user interface engagement mechanism can engage the first engagement mechanism to position the user interface module in the first orientation, and can engage the second engagement mechanism to position the user interface module in the second orientation. The user interface module can be secured in the first and second orientations by a fastener that extends through the user interface module and engages the top panel. The channel can also include a central hub that extends from the channel and through which an electrical cable can extend from an interior of the cabinet to an exterior. The central hub can prevent water from entering the cabinet. 
     In some embodiments, the top can include at least one hook that is configured to engage one of the first and second side panels and secure the top panel to the first or second side panels. The top panel can be removed from the cabinet and secured to the first or second side panel by the hook. 
     In other embodiments of the present disclosure, the cabinet can include a dual junction box. The dual junction box can have an elongated body, a first cover, and a second cover. The elongated body can have a first side, a second side, and an interior wall positioned between the first and second sides. The first cover can engage the first side of the elongated body and form a first chamber. The second cover can engage the second side of the elongated body and form a second chamber. The first and second chambers can be electrically isolated from each other by the interior wall. A first wire port can be positioned within the first chamber and extend through the cabinet. The first wire port can be configured to have a first wire of a first voltage level extend therethrough from an interior of the cabinet to the first chamber. A second wire port can be positioned within the second chamber and extend through the cabinet. The second wire port can be configured to have a second wire of a second voltage level extend therethrough from an interior of the cabinet to the second chamber. A first opening can be formed between the first cover and the body which can provide access to the first chamber and can be configured to receive a first cable of the first voltage level to extend into the first chamber and be connected with the first wire. A second opening can be formed between the second cover and the body which can provide access to the second chamber an can be configured to allow a second cable of the second voltage level to extend into the second chamber and be connected with the second wire. 
     In some aspects, the first chamber can be a low-voltage chamber and the second chamber can be a high-voltage chamber. In additional aspects, the first wire can be a low-voltage wire, the first cable can be a low-voltage cable, the second wire can be a high-voltage wire, and the second cable can be a high-voltage cable. 
     In other aspects, the first cover and the first side of the elongated body can form a first opening, and the second cover and the second side of the elongated body can form a second opening. The first opening can be configured to receive and secure the first wire in place, and the second opening can be configured to receive and secure the second wire in place. 
     In some embodiments of the present disclosure, the gas heater can also include a gas valve having an inlet and an outlet. The inlet of the gas valve can be connected to an outlet of a first component. The outlet of the gas valve can be connected to an inlet of a second component. The inlet of the gas valve can be secured to the outlet of the first component by a first quick disconnect fitting, while the outlet of the gas valve can be secured to the inlet of the second component by a second quick disconnect fitting. The first and second quick disconnect fittings can have a body, a first end, and a second end. The body can define first and second elongated slots that extend between the first and second ends. The first and second elongated slots can be configured to receive at least a portion of the gas valve inlet and at least a portion of the first component outlet. The first and second elongated slots can also be configured to receive at least a portion of the gas valve outlet and at least a portion of the second component inlet. In some embodiments, the inlet of the gas valve can include a piston-style connector that is received by the outlet of the first component, and the inlet of the second component can include a piston-style connected that is received by the outlet of the gas valve. 
     In accordance with embodiments of the present disclosure, an exemplary gas heater is provided that includes a cabinet, a combustion chamber canister, a tube sheet, a heat exchanger, a water header manifold, a combustion blower, a burner, an igniter, and a mount. The cabinet can include a first side panel, a second side panel, an exhaust side panel, a water header side panel, a bottom, and a top. The combustion chamber canister can have a top opening and an open end that is covered by the tube sheet which can be mounted to the combustion chamber canister. The heat exchanger, which includes at least one tube and can define a combustion chamber, can be positioned within the combustion chamber canister and configured to extract heat from hot gases within the combustion chamber. The water header manifold can be mounted to the tube sheet and can route water through the heat exchanger. The combustion blower discharges combustible gas through a pipe that extends from the combustion blower to a central opening in the tube sheet, thus providing the combustible gas to the burner that is mounted to the tube sheet opposite the pipe. The burner includes a positioning flange extending along a length thereof, and dissipates the combustible gas that it receives from the combustion blower via the pipe. The mount can include a body, a mounting flange surrounding the body, and igniter mount, and a spacing flange extending from the body. The mount can be mounted to the combustion chamber canister with a portion of the mount extending through the top opening of the combustion chamber canister and a gap being formed between the mounting flange and the combustion chamber canister. A gasket can be positioned in the gap between the mounting flange and the combustion chamber canister. The igniter can be mounted to the igniter mount, and can extend through the mount into the combustion chamber where it is positioned a first distance from the burner. The igniter is configured to ignite the gas mixture dissipated by the burner. When the mount is mounted to the combustion chamber canister, the spacing flange of the mount can engage the positioning flange of the burner to tie the burner and the mount together to maintain the first distance substantially constant. Additionally, engagement of the spacing flange with the mounting flange can allow the burner to move along its longitudinal axis, while preventing the burner from moving away from the mount and the igniter and alternating the first distance. The gasket can be configured to absorb an accumulation of tolerance variations of the gas heater and ensure that the spacing flange of the mount engages the positioning flange of the burner. 
     In some embodiments the gas heater can also include a flame sensor that is mounted to the mount. The flame sensor extends through the mount into the combustion chamber where it is positioned a second distance from the burner. Engagement of the spacing flange with the mounting flange can tie the burner and the mount together such that the second distance is substantially constant. 
     In some embodiments of the present disclosure, an adaptable water manifold for a pool or spa gas heater is provided that includes an inflow tube, an inlet, an outflow tube, and an outlet. The inflow tube is in fluidic communication with the inlet, and can be configured to engage and provide water to one or more heat exchanger tubes. The outflow tube is in fluidic communication with the outlet, and can be configured to engage and receive water from the one or more heat exchanger tubes. When the adaptable water manifold is mounted to the gas heater, the inlet is positioned at an inlet position, and the outlet is positioned at an outlet position. For example, the first position can include an inlet height, which can be the distance between the center of the inlet and the bottom of the gas heater, and the second position can include an outlet height, which can be the distance between the center of the outlet and the bottom of the gas heater. The inlet includes one or more inlet mounts, and is configured to have an inlet fitting connected thereto. The inlet fitting includes one or more inlet fitting mounts and an inlet fitting outlet in fluidic communication with an inlet fitting inlet configured to engage pre-existing piping. The inlet fitting can be connected to the inlet through engagement of the inlet fitting mounts with the inlet mounts such that the inlet fitting outlet is adjacent to and in fluidic communication with the inlet. The outlet includes one or more outlet mounts, and is configured to have an outlet fitting connected thereto. The outlet fitting includes one or more outlet fitting mounts and an outlet fitting inlet in fluidic communication with an outlet fitting outlet configured to engage pre-existing piping. The outlet fitting can be connected to the outlet through engagement of the outlet fitting mounts with the outlet mounts such that the outlet fitting inlet is adjacent to and in fluidic communication with the outlet. When the inlet fitting is connected to the inlet, the inlet fitting outlet is at the inlet position and the inlet fitting inlet is at an adjusted inlet position. When the outlet fitting is connected to the outlet, the outlet fitting inlet is at the outlet position and the outlet fitting outlet is at an adjusted outlet position. In some embodiments, the inlet fitting operatively changes the position of the inlet to the location of the inlet fitting inlet, and the outlet fitting operatively changes the position of the location of the outlet to the outlet fitting outlet. In other embodiments, the inlet fitting height can be different than the inlet height and the outlet fitting height can be different than the outlet height. 
     In some embodiments, the inlet fitting can have an inlet fitting body that extends between the inlet fitting inlet and the inlet fitting outlet that places them in fluidic communication, and the outlet fitting can have an outlet fitting body that extends between the outlet fitting inlet and the outlet fitting outlet that places them in fluid communication. In other embodiments, the inlet fitting inlet can include a connector and the outlet fitting outlet can include a connector. In still other embodiments, the inlet can include one or more mounting flanges, the outlet can include one or more mounting flanges, the inlet fitting can include one or more inlet mounts, and the outlet fitting can include one or more outlet mounts. The inlet mounts can be secured to the one or more mounting flanges of the inlet to mount the inlet fitting to the inlet. The outlet mounts can be secured to the one or more mounting flanges of the outlet to mount the outlet fitting to the outlet. 
     In accordance with embodiments of the present disclosure, a heat exchanger for a swimming pool or spa gas heater is provided that includes one or more heat exchanger tubes, upper insulation, and lower insulation, which form a combustion chamber. The one or more heat exchanger tubes include an interior tube and a plurality of fins extending from the interior tube, which in some aspects can be welded to the tube or extruded from the tube. The interior tube include an inlet, an outlet, and a U-shaped body that extends from the inlet to the outlet. The upper insulation can be positioned on the top of the one or more heat exchanger tubes, and the lower insulation can be positioned on the bottom of the one or more heat exchanger tubes. The upper insulation and the lower insulation can reduce heat loss and direct hot gasses across the fins of the one or more heat exchanger tubes. The one or more heat exchanger tubes can be configured to be connected to a water header manifold that can route water through the interior tube. In some embodiments, the heat exchanger can include a plurality of heat exchanger tubes that are in a stacked arrangement. 
     In some embodiments, the plurality of fins can have one or more bent edges and a rounded edge. In such embodiments, the one or more bent edges can include four bent edges, and each of the four bent edges can comprise ⅙th of the circumference of the fin, and the one rounded edge can comprise ⅓ rd  of the circumference of the fin. The bent edges can form first, second, third, and fourth sides of the heat exchanger tube. According to other aspects, such a heat exchanger can include a plurality of heat exchanger tubes that are stacked with a first side of a first heat exchanger tube being adjacent a second side of a second heat exchanger tube. 
     In accordance with embodiments of the present disclosure, a heat exchanger for a swimming pool or spa gas heater is provided that includes a plurality of tube-and-fin subassemblies. Each of the tube-and-fin subassemblies includes a first tube, a second tube, and a plurality of fins secured to the first and second tubes. The first tube can include a first leg, a second leg, and a curved portion extending between the first and second legs, while the second tube can include a third leg, a fourth leg, and a curved portion extending between the third and fourth legs. The fins can include a body having four holes extending therethrough. The holes can be surrounded by collars that assist in securing the fins to the first and second tubes. The first leg can extend through one of the four holes, the second leg can extend through the second of the four holes, the third leg can extend through the third of the four holes, and the fourth leg can extend through the fourth of the four holes. Each of the fins can also have a first sidewall and a second sidewall that are positioned on opposite sides of the body. Each of the fins can also include a plurality of flanges that form channels for hot gases to pass through. The flanges can be configured to slow down hot gases passing across the fins and direct the hot gases into the channels. The plurality of tube-and-fin subassemblies can be positioned adjacent to each other in a semi-circular configuration with the first sidewall of the first tube-and-fin subassembly fins abutting the second sidewall of the second tube-and-fin subassembly fins. The heat exchanger can also include a front manifold, a tube sheet, a first insulation, and a second insulation, which the first, second, third, and fourth legs extend through. The first insulation can be positioned adjacent an interior side of the front manifold, and the second insulation can be positioned adjacent an interior side of the tube sheet. The plurality of tube-and-fin subassemblies can be positioned with the plurality of fins thereof between the front manifold and the tube sheet. 
     In some embodiments, the heat exchanger can comprise a plurality of, e.g., five or more, tube-and-fin subassemblies that are positioned adjacent to each other in a semi-circular fashion. In such embodiments, the first sidewall of the fins can be at a first angle from a vertical axis and the second sidewall of the fin can be at a second angle from the vertical axis. The sum of the first and second angles can be equal to sixty degrees. In some embodiments, the sum of the first and second angles can be equal to three-hundred and sixty (360) divided by the number of tube-and-fin subassemblies required to form a complete circle. 
     In another embodiment, the fins can include one or more flow directors that are configured to enhance the heat transfer of the fins. The flow directors can be louvers, lances, bumps, holes, extrusions, embosses, or ribs. 
     In accordance with embodiments of the present disclosure, a gas heater for a swimming pool or spa is provided that includes a cabinet that defines an interior, a combustion chamber, a heat exchanger, a burner, and a water header manifold. The heat exchanger can include at least one tube having a tube inlet and a tube outlet, and can be positioned at least partially within the combustion chamber. The heat exchanger can be configured to extract heat from hot gases in the combustion chamber. The burner can be positioned within the combustion chamber, and can receive combustible gas from a combustion blower. The burner can be configured to dissipate the combustible gas. The water header manifold can have an inlet in fluidic communication with the tube inlet and an outlet in fluidic communication with the tube outlet. The water header manifold can circulate water through the at least one tube of the heat exchanger. The combustion chamber, the heat exchanger, and the burner can be positioned within the interior of the cabinet with a first gap between a first side of the cabinet and the combustion chamber, and a second gap between a second side of the cabinet and the combustion chamber. The first gap reduces the amount of heat transferred from the combustion chamber to the first side of the cabinet, while the second gap reduces the amount of heat transferred from the combustion chamber to the second side of the cabinet. 
     In accordance with embodiments of the present disclosure, a cabinet for a swimming pool or spa gas heater is provided that includes a main body, a top panel, and a user interface module. The main body can define an interior, while the top panel can be configured to be placed on the main body. The top panel can have a first lateral side, a second lateral side, a channel extending between the first lateral side and the second lateral side, a first engagement mechanism positioned at a first end of the channel, and a second engagement mechanism positioned at a second end of the channel. The user interface module can include an elongated body, a user interface, and a user interface engagement mechanism. The user interface module can be configured to be placed within the channel. Specifically, the user interface module can be positioned in the channel in a first orientation with the user interface engagement mechanism engaged with the first engagement mechanism and the user interface accessible by a user from a first side of the main body, and a second orientation with the user interface engagement mechanism engaged with the second engagement mechanism and the user interface accessible by a user from a second side of the main body opposite the first side of the main body. 
     In accordance with embodiments of the present disclosure, a gas heater for a swimming pool or spa is provided that includes a main body, a top panel, a heater subassembly, a user interface module, and a control cable. The main body can define an interior, while the top panel can be configured to be placed on the main body. The top panel can have a first lateral side, a second lateral side, a channel extending between the first lateral side and the second lateral side, a first engagement mechanism positioned at a first end of the channel, and a second engagement mechanism positioned at a second end of the channel. The heater subassembly can be positioned within the interior of the main body, and can include a combustion chamber, a heat exchanger positioned at least partially within the combustion chamber, a burner, a printed circuit board including a controller, a water header manifold that can be configured to circulate water through the heat exchanger. The heat exchanger can be configured to extract heat from hot gases in the combustion chamber. The burner can receive combustible gas from a combustion blower and can be configured to dissipate the combustible gas into the combustion chamber. The user interface module can include an elongated body, a user interface, and a user interface engagement mechanism. The control cable can be electrically connected between the printed circuit board and the user interface controller. The user interface module can be configured to be placed within the channel. Specifically, the user interface module can be positioned in the channel in a first orientation with the user interface engagement mechanism engaged with the first engagement mechanism and the user interface accessible by a user from a first side of the main body, and a second orientation with the user interface engagement mechanism engaged with the second engagement mechanism and the user interface accessible by a user from a second side of the main body opposite the first side of the main body. 
     In accordance with embodiments of the present disclosure, a gas heater for a swimming pool or spa is provided that includes a main body, a top panel having at least one hanging device, and a heater subassembly positioned within an interior of the main body. The top panel can be configured to be placed on the main body covering the interior, and can be removed from the main body and secured to a first side panel of the main body through engagement of the at least one hanging device with the first side panel to provide access to the heater subassembly contained within the interior of the main body. 
     In accordance with embodiments of the present disclosure, a cabinet for a swimming pool or spa gas heater is provided that includes a main body defining an interior, a dual junction box positioned on a side panel of the main body, a first wire port, and a second wire port. The dual junction box can include a body, a first cover, and a second cover. The body can define a first chamber and a second chamber, where the first chamber is electrically isolated from the second chamber. The first cover can be configured to removably engage the body and cover the first chamber, while the second cover can be configured to removably engage the body and cover the second chamber. A first hole can extend through the body into the first chamber, and can be configured to receive a first electrical cable of a first voltage level. A second hole can extend through the body into the second chamber, and can be configured to receive a second electrical cable of a second voltage level that is greater than the first voltage level. In some embodiments, the first hole can include a first grommet positioned therein, and the second hole can include a second grommet positioned therein. The first wire port can extend through the side panel of the main body from the interior of the main body to the first chamber, and can be configured to have a first wire extend therethrough from the interior of the main body into the first chamber. The second wire port can extend through the side panel of the main body from the interior of the main body to the second chamber, and can be configured to have a second wire extend therethrough from the interior of the main body into the second chamber. 
     In some embodiments, the first cover can define a portion of the first chamber when removably engaged with the body, and/or the second cover can define a portion of the second chamber when removably engaged with the body. In other aspects, the body can include a first open side and a second open side such that the first chamber is accessible through the first open side and the second chamber is accessible through the second open side. 
     In other embodiments, the first and second covers can be configured to be removably secured to the main body. In such embodiments, the main body can include a first slot and a second slot, while the first cover can include a first protrusion and the second cover can include a second protrusion. The first slot can be configured to receive the first protrusion to removably secure the first cover to the main body, and the second slot can be configured to receive the second protrusion to removably secure the second cover to the main body. 
     In some embodiments, the first chamber can be a low-voltage chamber and the second chamber can be a high-voltage chamber. In other embodiments, the first wire can be a low-voltage wire, the first electrical cable can be a low-voltage cable, the second wire can be a high-voltage wire, and the second electrical cable can be a high-voltage cable. 
     In accordance with embodiments of the present disclosure, a gas heater for a swimming pool or spa is provided that includes a main body defining an interior, a heater subassembly positioned within the interior of the main body, a dual junction box positioned on a side panel of the main body, a first wire port, and a second wire port. The heater subassembly can include one or more low-voltage components electrically connected with a low-voltage wire and one or more high-voltage components electrically connected with a high-voltage wire. The dual junction box can include a body, a first cover, and a second cover. The body can define a first chamber and a second chamber, where the first chamber is electrically isolated from the second chamber. The first cover can be configured to removably engage the body and cover the first chamber, while the second cover can be configured to removably engage the body and cover the second chamber. A first hole can extend through the body into the first chamber, and can be configured to receive a low-voltage electrical cable of a first voltage level. A second hole can extend through the body into the second chamber, and can be configured to receive a high-voltage electrical cable of a second voltage level that is greater than the first voltage level. In some embodiments, the first hole can include a first grommet positioned therein, and the second hole can include a second grommet positioned therein. The first wire port can extend through the side panel of the main body from the interior of the main body to the first chamber, and can be configured to have the low-voltage wire extend therethrough from the interior of the main body into the first chamber. The second wire port can extend through the side panel of the main body from the interior of the main body to the second chamber, and can be configured to have the high-voltage wire extend therethrough from the interior of the main body into the second chamber. 
     In some embodiments, the first cover can define a portion of the first chamber when removably engaged with the body, and/or the second cover can define a portion of the second chamber when removably engaged with the body. In other aspects, the body can include a first open side and a second open side such that the first chamber is accessible through the first open side and the second chamber is accessible through the second open side. 
     In other embodiments, the first and second covers can be configured to be removably secured to the main body. In such embodiments, the main body can include a first slot and a second slot, while the first cover can include a first protrusion and the second cover can include a second protrusion. The first slot can be configured to receive the first protrusion to removably secure the first cover to the main body, and the second slot can be configured to receive the second protrusion to removably secure the second cover to the main body. 
     In some embodiments, the first chamber can be a low-voltage chamber and the second chamber can be a high-voltage chamber. 
     In accordance with embodiments of the present disclosure, a gas heater for a swimming pool or spa is provided that includes a cabinet defining an interior, a combustion chamber enclosure, a heat exchanger, a water header manifold, a burner, a combustion blower, and an igniter. The combustion chamber enclosure can include a top having a burner opening, and can define a combustion chamber cavity. The heat exchanger can include at least one tube having a tube inlet and a tube outlet, can be positioned at least partially within the combustion chamber cavity, and can be configured to extract heat from hot gases in the combustion chamber. The water header manifold can include an inlet in fluidic communication with the tube inlet and an outlet in fluidic communication with the tube outlet, and can circulate water through the at least one tube of the heat exchanger. In some embodiments, the inlet of the water header manifold can be configured to receive water to be heated from a pool or spa, and the outlet can be configured to provide heated water back to the pool or spa. The burner can include a gas opening and a discharge plate, and can be mounted to the combustion chamber enclosure adjacent the burner opening. The burner can be configured to dissipate combustible gas from the discharge plate into the combustion chamber cavity. In some embodiments, the discharge plate can be a mesh plate. The combustion blower can be mounted to the burner and can be configured to discharge combustible gas through the gas opening and into the burner. The igniter can be mounted to the burner and can extend into the combustion chamber cavity. The igniter can be positioned a first distance from the discharge plate and can be configured to ignite the combustible gas dissipated by the burner into the combustion chamber cavity. Because the igniter is engaged with the burner, the first distance can be maintained substantially constant. 
     In some embodiments, the burner can include a box-like body that extends into the combustion chamber cavity, and the discharge plate can be positioned at a bottom of the box-like body. In such embodiments, the heat exchange can define a combustion region and the burner can dissipate the combustion gas into the combustion region. In other such embodiments, the heat exchanger can be a semi-circular heat exchanger that defines a top gap, and the box-like body of the burner can be positioned at least partially in the top gap. The heat exchange can include front insulation and rear insulation, and the front insulation can include a cutout configured to receive the igniter. In still other such embodiments, the burner can include a top plate that includes a gas opening, and the combustion blower can be mounted to the top plate with an outlet of the combustion blower being positioned adjacent the gas opening. 
     In other embodiments, the gas heater can include a flame sensor that is mounted to the burner and extends into the combustion chamber cavity where it can be positioned a second distance from the discharge plate. Engagement of the flame sensor with the burner can maintain the second distance substantially constant. 
     In still other embodiments, the gas heater can include a tube sheet that has a first side and a second side, and the combustion chamber enclosure can include an open side. In such embodiments, the combustion chamber enclosure can be secured to the first side of the tube sheet with the tube sheet covering the open end of the combustion chamber enclosure, and the tube inlet and the tube outlet can extend through the tube sheet from the first side to the second side. Additionally, in such embodiments, the water header manifold can be mounted to the second side of the tube sheet, and may be accessible from a water header side of the cabinet. 
     In additional embodiments, the gas heater can include an exhaust pipe that extends from the combustion chamber enclosure, and which can be configured to receive exhaust fumes from the combustion chamber cavity and discharge the exhaust fumes from the gas heater. In such embodiments, the exhaust pipe can extend from the combustion chamber enclosure to an exhaust side of the cabinet. 
     In some embodiments, the igniter and/or the burner can be accessible through a top of the cabinet. In other embodiments, the gas heater can include a controller positioned within the cabinet, and the controller can be accessible through a top of the cabinet. 
     In accordance with embodiments of the present disclosure, an adaptable water manifold for a swimming pool or spa gas heater is provided that includes an inlet, an outlet, an inflow section, an outflow section, an inlet fitting, and an outlet fitting. The inlet can be positioned at an inlet position when the adaptable water manifold is mounted to the gas heater. The outlet can be positioned at an outlet position when the adaptable water manifold is mounted to the gas heater. The inflow section can be in fluidic communication with the inlet and can be configured to provide water to one or more heat exchanger tubes, while the outflow section can be in fluidic communication with the outlet and can be configured to receive water from one or more heat exchanger tubes. The inlet fitting can have an inlet fitting inlet in fluidic communication with an inlet fitting outlet. The inlet fitting can be connectable to the inlet with the inlet fitting outlet adjacent the inlet. The outlet fitting can have an outlet fitting inlet in fluidic communication with an outlet fitting outlet. The outlet fitting can be connectable to the outlet with the outlet fitting inlet adjacent the outlet. When the inlet fitting is connected to the inlet, the inlet fitting outlet is at the inlet position and the inlet fitting inlet is at an adjusted inlet position. When the outlet fitting is connected to the outlet, the outlet fitting inlet is at the outlet position and the outlet fitting outlet is at an adjusted outlet position. The adjusted inlet position can be associated with the inlet of a water manifold of a second heater that is different than the swimming pool or spa gas heater, while the adjusted outlet position can be associated with an outlet of the water manifold of the second heater that is different than the swimming pool or spa gas heater. 
     In accordance with embodiments of the present disclosure, a heat exchanger for a swimming pool or spa gas heater is provided that includes a plurality of tube-and-fin subassemblies. Each of the plurality of tube-and-fin subassemblies can include a first tube, a second tube, a third tube, a first plurality of fins, and a second plurality of fins. The first tube can extend through the first plurality of fins. The second tube can extend through the first plurality of fins and the second plurality of fins. The third tube can extend through the second plurality of fins. The first plurality of fins can be positioned adjacent the second plurality of fins, and the plurality of tube-and-fin subassemblies can be positioned in a semi-circular configuration. 
     In accordance with embodiments of the present disclosure, a water header manifold for a heat exchanger is provided that includes a main body, a circulation body, a first cartridge, and a second cartridge. The main body can include an inflow section and an outflow section. The inflow section can define an inflow chamber, and can include an inlet and a plurality of inlet ports in fluidic communication with the inflow chamber. The inlet can be configured to receive water to be heated from a pool or spa plumbing system, and the plurality of inlet ports can be configured to be placed in fluidic communication with a heat exchanger. The outflow section can define an outflow chamber, and can include an outlet and a plurality of outlet ports in fluidic communication with the outflow chamber. The outlet can be configured to provide heated water to the pool or spa plumbing system, and the plurality of outlet ports can be configured to be placed in fluidic communication with the heat exchanger. The circulation body can include a plurality of inlet ports, which can be configured to be placed in fluidic communication with the heat exchanger, and a plurality of outlet ports, which can be configured to be placed in fluidic communication with the heat exchanger. The first cartridge and the second cartridge can be positioned within the circulation body. The first cartridge, the second cartridge, and the circulation body can define a plurality of chambers, where each of the plurality of inlet ports can be configured to provide water to a heat exchanger tube from one of the plurality of chambers or the inflow chamber, and each of the plurality of outlet ports can be configured to receive water from a heat exchanger and discharge the received water into one of the plurality of chambers or the outflow chamber. Additionally, the plurality of chambers can direct water between the plurality of inlet ports and the plurality of outlet ports causing the water to circulate through an associated heat exchanger and from the inlet to the outlet. 
     Other objects and features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To assist those of skill in the art in making and using the disclosed compact universal gas pool heater and associated methods, reference is made to the accompanying figures, wherein: 
         FIG.  1    is a first perspective view of an exemplary compact universal gas pool heater in accordance with embodiments of the present disclosure; 
         FIG.  2    is a second perspective view of the compact universal gas pool heater of  FIG.  1   ; 
         FIG.  3    is a third perspective view of the compact universal gas pool heater of  FIG.  1   ; 
         FIG.  4    is a first elevational view of the compact universal gas pool heater of  FIG.  1    showing an exhaust side panel having an exhaust vent, a gas inlet, and electrical junction boxes; 
         FIG.  5    is a second elevational view of the compact universal gas pool heater of  FIG.  1    showing a water header side panel; 
         FIG.  6    is a top plan view of the compact universal gas pool heater of  FIG.  1   ; 
         FIG.  7    is an exploded perspective view of a cabinet of the compact universal gas pool heater of  FIG.  1   ; 
         FIG.  8    is an exploded perspective view of the compact universal gas pool heater of  FIG.  1    showing a user interface module separated from a cabinet top; 
         FIG.  9    is a bottom perspective view of the user interface module of  FIG.  8   ; 
         FIG.  10    is a perspective view of the compact universal gas pool heater of  FIG.  1    showing the cabinet top removed and removably secured on a side of the cabinet; 
         FIG.  11    is an elevational view of the compact universal gas pool heater of  FIG.  10    showing the cabinet top removed and removably secured on a side of the cabinet; 
         FIG.  12    is an exploded elevational view of the compact universal gas pool heater of  FIG.  1    showing the exhaust side panel with first and second covers of a dual junction box exploded; 
         FIG.  13    is a sectional view of the compact universal gas pool heater taken along Line  13 - 13  of  FIG.  6   ; 
         FIG.  14    is an exploded perspective view showing details of the dual junction box with the second cover exploded; 
         FIG.  15    is perspective view of the compact universal gas pool heater of  FIG.  1    with the cabinet top and side panels removed; 
         FIG.  16 A  is a side elevational view of the compact universal gas pool heater of  FIG.  15   ; 
         FIG.  16 B  is a top plan view of the compact universal gas pool heater of  FIG.  15   ; 
         FIG.  17    is an enlarged view of Area  FIG.  17    of  FIG.  16 A  showing a gas valve including quick disconnect fittings; 
         FIG.  18    is an exploded view of the gas valve and quick disconnect fittings of  FIG.  17   ; 
         FIG.  19    is a perspective view of the quick disconnect fitting of  FIG.  17   ; 
         FIG.  20    is a perspective view of the quick disconnect fitting of  FIG.  17    assembled on a gas valve; 
         FIG.  21    is a first exploded perspective view of the compact universal gas pool heater of  FIG.  1    with the cabinet top and side panels removed; 
         FIG.  22    is a second exploded perspective view of the compact universal gas pool heater of  FIG.  1    with the cabinet top and side panels removed; 
         FIG.  23    is a third exploded perspective view of the compact universal gas pool heater of  FIG.  1    with the cabinet top and side panels removed; 
         FIG.  24 A  is a perspective view of a heat exchanger of the compact universal gas pool heater; 
         FIG.  24 B  is a top plan view of the heat exchanger of  FIG.  24 A ; 
         FIG.  25    is a detailed view of a heat exchanger tube of the heat exchanger shown in  FIG.  24 A ; 
         FIG.  26 A  is a sectional view taken along Line  26 A- 26 A of  FIG.  16 B  showing the interior of a combustion chamber canister; 
         FIG.  26 B  is a perspective sectional view corresponding to the sectional view shown in  FIG.  26 B ; 
         FIG.  27    is a sectional view taken along Line  27 - 27  of  FIG.  16 B  showing the interior of the combustion chamber canister and heat exchanger; 
         FIG.  28    is a sectional view taken along Line  28 - 28  of  FIG.  16 B  showing the interior of the combustion chamber canister and heat exchanger; 
         FIG.  29    is a perspective sectional view corresponding to the sectional view shown in  FIG.  28   ; 
         FIG.  30    is a top plan view of the compact universal gas pool heater of  FIG.  1    with the cabinet top panel removed; 
         FIG.  31    is a sectional view taken along Line  31 - 31  of  FIG.  16 B  showing the flow path between the heat exchanger and a water manifold header; 
         FIG.  32    is a sectional view taken along Line  32 - 32  of  FIG.  16 B  showing the interior of the water manifold header in perspective; 
         FIG.  33    is a perspective view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header without fittings connected; 
         FIG.  34    is an elevational view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header without fittings connected; 
         FIG.  35    is a perspective view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header with a first inlet fitting and a first outlet fitting connected; 
         FIG.  36    is an elevational view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header with the first inlet and first outlet fittings connected; 
         FIG.  37    is a perspective view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header with a second inlet fitting and a second outlet fitting connected; 
         FIG.  38    is an elevational view of the compact universal gas pool heater of  FIG.  1    showing the water manifold header with the second inlet and second outlet fittings connected; 
         FIG.  39    is a perspective view of the combustion chamber canister and a second tube sheet housing a second heat exchanger according to another aspect of the present disclosure; 
         FIG.  40    is an elevational view of the combustion chamber canister and second tube sheet shown in  FIG.  39   ; 
         FIG.  41    is a first perspective view of the second heat exchanger mounted to the second tube sheet; 
         FIG.  42    is a second perspective view of the second heat exchanger mounted to the second tube sheet; 
         FIG.  43    is a sectional view taken along Line  43 - 43  of  FIG.  40   ; 
         FIG.  44    is a perspective sectional view taken along Line  43 - 43  of  FIG.  40   ; 
         FIG.  45    is a perspective view of a fin of the second heat exchanger of  FIG.  41   ; 
         FIG.  46    is an elevational view of the fin of  FIG.  45   ; 
         FIG.  47    is a perspective view showing two tubes being inserted into the fin of  FIG.  45   ; 
         FIG.  48    is a perspective view showing two tubes inserted through three fins in accordance with  FIG.  45   ; 
         FIG.  49    is an elevational view of an alternative fin according to aspects of the present disclosure; 
         FIG.  50    is a sectional view taken along Line  50 - 50  of  FIG.  49   ; 
         FIG.  51    is a first perspective view of an exemplary compact universal gas pool heater in accordance with embodiments of the present disclosure; 
         FIG.  52    is a second perspective view of the compact universal gas pool heater of  FIG.  51   ; 
         FIG.  53    is a first elevational view of the compact universal gas pool heater of  FIG.  51    showing an exhaust side panel having an exhaust vent, a gas inlet, and a dual electrical junction box; 
         FIG.  54    is a second elevational view of the compact universal gas pool heater of  FIG.  51    showing a water header side panel; 
         FIG.  55    is an exploded perspective view of the compact universal gas pool heater of  FIG.  51    showing a user interface module separated from a cabinet top panel; 
         FIG.  56    is a partial perspective view of the gas pool heater of  FIG.  51    with the user interface module removed from the cabinet top panel; 
         FIG.  57    is a bottom perspective view of the user interface module of  FIG.  55   ; 
         FIG.  58    is a partial perspective view of the gas pool heater of  FIG.  51    with the cabinet top panel removed; 
         FIG.  59    is a top plan view of the gas pool heater of  FIG.  51    with the cabinet top panel removed; 
         FIG.  60    is a partially exploded elevational view of the compact universal gas pool heater of  FIG.  51    showing the exhaust side panel with first and second covers of the dual junction box exploded; 
         FIG.  61    is a sectional view of the compact universal gas pool heater taken along Line  61 - 61  of  FIG.  59   ; 
         FIG.  62    is an exploded partial perspective view showing details of the dual junction box of the compact universal gas pool heater of  FIG.  51    with the second cover exploded; 
         FIG.  63    is a first perspective view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  64    is a second perspective view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  65    is a top plan view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  66    is a first exploded perspective view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  67    is a second exploded perspective view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  68    is a third exploded perspective view of the compact universal gas pool heater of  FIG.  51    with the cabinet top and side panels removed; 
         FIG.  69    is a perspective view of a heat exchanger of the compact universal gas pool heater of  FIG.  51   ; 
         FIG.  70    is a top plan view of the heat exchanger of  FIG.  69   ; 
         FIG.  71    is a front elevational view of the heat exchanger of  FIG.  69   ; 
         FIG.  72    is a rear elevational view of the heat exchanger of  FIG.  69   ; 
         FIG.  73    is a perspective view of a fin of the second heat exchanger of  FIGS.  69 - 72   ; 
         FIG.  74    is an elevational view of the fin of  FIG.  73   ; 
         FIG.  75    is a perspective view showing three tubes being inserted into two fins in accordance with  FIG.  73   ; 
         FIG.  76    is a perspective view showing three tubes inserted through nine fins in accordance with  FIG.  73   ; 
         FIG.  77    is a sectional view taken along Line  77 - 77  of  FIG.  65    showing the interior of a combustion chamber enclosure and the heat exchanger; 
         FIG.  78    is a perspective sectional view corresponding to the sectional view shown in  FIG.  77   ; 
         FIG.  79    is a front perspective view of a second water manifold header of the present disclosure; 
         FIG.  80    is a rear perspective view of the second water manifold header of  FIG.  79   ; 
         FIG.  81    is an exploded perspective view of the second water manifold header of  FIGS.  79  and  80   ; 
         FIG.  82    is a sectional view taken along Line  82 - 82  of  FIG.  65    showing the interior of the second water manifold header in perspective; 
         FIG.  83    is a sectional view taken along Line  82 - 82  of  FIG.  65    showing the interior of the second water manifold header; 
         FIG.  84    is a partial perspective view of a gas heater of the present disclosure incorporating an alternative burner connected with the blower and the combustion chamber enclosure of  FIG.  63   ; 
         FIG.  85    is a top plan view of the gas heater of  FIG.  84   ; 
         FIG.  86    is a partially exploded perspective view of the blower, combustion chamber enclosure, and burner of  FIG.  84   ; 
         FIG.  87    is a bottom perspective view of the burner of  FIGS.  84 - 86   ; 
         FIG.  88    is a sectional view taken along Line  88 - 88  of  FIG.  85   ; and 
         FIG.  89    is a perspective view showing a third inlet fitting and a third outlet fitting of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE 
     In accordance with embodiments of the present disclosure, exemplary compact universal gas pool heaters are provided that allow for increased functionality and serviceability, as well as enhanced adaptability of the compact universal gas pool heater to various installation requirements and locations. 
     With initial reference to  FIGS.  1 - 6   , a compact universal gas pool heater  10  (hereinafter “gas heater  10 ”) includes a cabinet  12  having a top panel  14  (e.g., a top), a user interface module  16 , a first side panel  18  (e.g., a first side), a second side panel  20  (e.g., a second side), an exhaust side panel  22  (e.g., an exhaust side or a third side), a water header side panel  24  (e.g., a water header side or a fourth side), and a base  26  (e.g., a bottom). The first side panel  18 , the second side panel  20 , the exhaust side panel  22 , and the water header side panel  24  can generally form a main body of the cabinet  12 . As shown in  FIGS.  1  and  4   , which are, respectively, a first perspective view of the gas heater  10  and an elevational view of the exhaust side panel  22 , the exhaust side panel  22  includes a dual junction box  28 , an exhaust vent  30 , a gas pipe opening  32 , a plurality of lower vents  34 , and a plurality of upper vents  36 . 
     The exhaust vent  30  is generally positioned at, and extends outward from, an upper portion of the exhaust side panel  22 . The exhaust vent  30  includes a body  38  having upper vents  40 , and is configured to receive a portion of an exhaust pipe from the interior of the cabinet  12 , allowing for exhaust fumes to exit the exhaust pipe and dissipate from the gas heater  10  through the top vents  40 . 
     The dual junction box  28  includes an elongated body  42 , a first cover  44 , and a second cover  46 . The elongated body  42  has a first open side  48  and a second open side  50  opposite the first open side  48 . The first open side  48  includes a first notch  52  that extends inwardly towards the second open side  50 , and the second open side  50  includes a second notch  54  that extends inwardly toward the first open side  48 . Accordingly, the first and second notches  52 ,  54  are on opposite sides of the elongated body  42 . The elongated body  42  also includes the gas pipe opening  32 , through which a gas inlet pipe  56  extends from the interior of the cabinet  12  to the exterior. The first and second covers  44 ,  46  each, respectively, includes a body  58 ,  60  and a locking extension  62 ,  64  extending therefrom. The first cover  44  can be inserted into, or placed over, the first open side  48  of the elongated body  42  with the locking extension  62  adjacent to and cooperating with the first notch  52 . Similarly, the second cover  46  can be inserted into, or placed over, the second open side  50  of the elongated body  42  with the locking extension  64  adjacent to and cooperating with the second notch  54 . The locking extension  62  of the first cover  44  cooperates with the first notch  52  to form a first opening  66  into the dual junction box  28 , while the locking extension  64  of the second cover  46  cooperates with the second notch  54  to form a second opening  68  into the dual junction box  28 . The first and second openings  66 ,  68  allow for electrical cables to be inserted into the dual junction box  28  and connected with high-voltage and low-voltage electrical wires of the gas heater  10 . The dual junction box  28  is discussed in greater detail in connection with  FIGS.  12 - 14   . 
     As shown in  FIGS.  2 ,  3 , and  5   , which are second and third perspective views of the gas heater  10 , and an elevational view of the water header side panel  24 , respectively, the water header side panel  24  includes a piping cover  70 , a water manifold inflow cutout  72 , a water manifold outflow cutout  74 , an air inlet opening  76  covered by a removable screen  78 , a plurality of lower vents  79   a , and a plurality of upper vents  79   b . The piping cover  70  extends outward from the water header side panel  24  and provides space for a combustion blower  80  and gas-mixture pipe  82  (see, e.g.,  FIG.  15   ) that extends from the combustion blower  80  to a burner  84  (see, e.g.,  FIG.  22   ). The air inlet opening  76  is generally positioned adjacent an air inlet pipe  86  of the combustion blower  80 , for example, it can be in the upper corner of the water header side panel  24  as shown in  FIG.  5   . The air inlet opening  76  allows for exterior air to be drawn therethrough, into the air inlet pipe  86 , and into the combustion blower  80  to be used for combustion. The air inlet opening  76  can be covered by the screen  78 , which can be removably secured to the water header side panel  24  by fasteners  88 . The water manifold inflow cutout  72  and the water manifold outflow cutout  74  allow for a water header manifold  90  to extend into the interior of the cabinet  12  and be mounted to a tube sheet  91  (see, e.g.,  FIG.  23   ). The water header manifold  90  is discussed in greater detail in connection with  FIGS.  31 - 38   . 
       FIG.  7    is an exploded perspective view of the cabinet  12 . As shown in  FIG.  7   , the cabinet  12  includes the top panel  14 , the user interface module  16 , the first side panel  18 , the second side panel  20 , the exhaust side panel  22 , the water header side panel  24 , and the base  26 . The exhaust side panel  22  includes an exhaust panel body  92  and the exhaust vent  30 . The exhaust panel body  92  includes a circular opening  94  that receives a portion of an exhaust pipe from the interior of the cabinet  12 , allowing for exhaust fumes to vent into the exhaust vent  30  and dissipate through the upper vents  36  of the exhaust vent  30 . The water header side panel  24  can be a single panel or can be formed of multiple components including a bottom panel  96 , a top panel  98 , a bottom piping cover  100 , and a first half  102  of the air inlet opening  76 . 
     The top panel  98  can include a top piping cover  104  and a second half  106  of the air inlet opening  76 . The top piping cover  104  cooperates with the bottom piping cover  100  to form the piping cover  70 , as shown in and described in connection with  FIG.  2   . The first half  102  and the second half  106  cooperate to form the air inlet opening  76 , as shown in and described in connection with  FIG.  5   , which the removable screen  78  is placed over. The top panel  14  generally includes a first lateral side  108 , a second lateral side  110 , and a central channel  112  that extends substantially the length of the top panel  14  between the first and second lateral sides  108 ,  110 . The central channel  112  is generally a recess that extends between the first and second lateral sides  108 ,  110 , and which is sized and configured to receive the user interface module  16 . The top panel  14  also includes first and second handles  114 ,  116  on opposite sides thereof (see, e.g.,  FIGS.  1  and  7   ) for readily grasping the top panel  14  and removing it from the remainder of the cabinet  12 , or for moving the entire gas heater  10 . The user interface module  16  includes an elongated body  118 , an electronics housing  120 , a user interface  122 , and a cover  124 . The user interface module  16  is sized and shaped to fit within the central channel  112  of the top panel  14 . 
       FIGS.  8  and  9    illustrate the user interface module  16  and the top panel  14  in greater detail. Specifically,  FIG.  8    is a partially exploded perspective view of the user interface module  16  separated from the top panel  14 , and  FIG.  9    is a bottom perspective view of the user interface module  16 . According to aspects of the present disclosure, the orientation of the user interface module  16  on the top panel  14  can be reversed in order to suit different installation positions and requirements. As shown in  FIG.  8   , the top panel  14  includes a central hub  126  that is positioned in, and extends from, the center of the central channel  112 . The central hub  126  defines a hole  128  that extends through the top panel  14  to the interior of the cabinet  12 . The hole  128  is configured to receive a multi-conductor cable (not shown) that is routed through the hole  128  and the central hub  126 , and connected to the user interface module  16 , thus placing the user interface module  16  in electrical communication with the interior electronics of the gas heater  10 . The central hub  126  is a raised wall that forces water, e.g., rain water, to flow there around, thus preventing water from flowing into the hole  128  and into the cabinet  12 . Accordingly, the cabinet  12  is resistant to the entry of water, which it may be exposed to due to the gas heater  10  being located outdoors and in contact with the elements, such as rain and snow. Additionally, the central channel  112  can be sloped from the center to the outside ends thereof, which forces water to flow outward and off of the top panel  14 , to prevent and/or inhibit pooling. The top panel  14  also includes first and second engagement mechanisms  130   a ,  130   b  (e.g., indentations or notches) on opposite ends of the central channel  112 , along with two fastener holes  132 . The engagement mechanisms  130   a ,  130   b  and fastener holes  132  are configured to assist with securing the user interface module  16  to the top panel  14 . 
     As shown in  FIG.  9   , the user interface module  16  also includes a central recess  134 , a fastener hole  136 , and a user interface engagement mechanism  138  (e.g., a hook or extension). The central recess  134  is positioned in the center of the user interface module  16  and extends into the electronics housing  120 . The central recess  134  is sized and configured to receive the central hub  126  of the top panel  14  when the user interface module  16  is mounted on the top panel  14 . The central recess  134  allows for the multi-conductor cable extending out from the central hub  126  to extend into the electronics housing  120  and electrically connect with the electronics of the user interface module  16 . The fastener hole  136  is generally positioned adjacent the cover  124  and extends through a curved front wall  140  of the elongated body  118 . When the user interface module  16  is positioned on the top panel  14 , the fastener hole  136  of the user interface module  16  will be aligned with either one of the fastener holes  132  of the top panel  14  such that a fastener  142 , e.g., a screw, a Christmas tree retainer, etc., can be inserted through the fastener holes  132 ,  136  to secure the user interface module  16  to the top panel  14 . The user interface engagement mechanism  138  extends from a curved rear wall  144  of the elongated body  118 , and is sized and shaped to extend into and engage the engagement mechanisms  130   a ,  130   b  of the top panel  14 . 
     To secure the user interface module  16  to the top panel  14 , a user first places the user interface engagement mechanism  138  into one of the engagement mechanisms  130   a ,  130   b , e.g., the second engagement mechanism  130   b , of the top panel  14  to prevent the user interface module  16  from longitudinal movement. The user then lowers the user interface module  16  into the central channel  112  so that the central hub  126  is inserted into the central recess  134  and the fastener hole  136  of the user interface module  16  is aligned with the fastener hole  132  of the top panel  14 . At this point, the user interface module  16  is positioned between the first and second lateral sides  108 ,  110  of the top panel  14 , which prevent the user interface module  16  from moving laterally. The user then inserts the fastener  142  into the fastener holes  132 ,  136  to fully secure the user interface module  16  to the top panel  14 . Specifically, the fastener  142  prevents vertical and rotational movement of the user interface module  16 . At this point, the user interface module  16  is in a first position. To change the orientation of the user interface module  16  to a second position, a user removes the fastener  142 , lifts the user interface module  16  vertically off of the top panel  14 , and rotates the user interface module  16  one-hundred and eighty (180) degrees about central axis A. The user then repeats the steps for securing the user interface module  16  to the top panel  14 , but instead of placing the user interface engagement mechanism  138  in the second engagement mechanism  130   b , the user interface engagement mechanism  138  is placed in the first engagement mechanism  130   a . The user then lowers the user interface module  16  until it rests in the central channel  112 , and inserts the fastener  142  into the fastener holes  132 ,  136  to fully secure the user interface module  16  to the top panel  14 . Thus, the user interface module  16  can be placed in two different configurations that are one-hundred and eighty (180) degrees opposite of each other without requiring the entire top  14  to be removed and rotated. That is, in the first position, the user interface  122  of the user interface module  16  is easily accessible by a user standing at the first side panel  18  of the cabinet  12 , while in the second position the user interface  122  of the user interface module  16  is easily accessible by a user standing at the second side panel  20  of the cabinet  12 . 
     When the user interface module  16  is secured to the top panel  14 , the top portion of the elongated body  118  lies flush with first and second lateral sides  108 ,  110  of the top panel  14 . However, the fit between the user interface module  16  and the first and second lateral sides  108 ,  110  of the top  14  need not be a rain-proof seal, instead a small gap can be provided that allows for water, e.g., rain water, to flow around and below the user interface module  16 , where it is channeled to the edges of the top panel  14  and runs off the gas heater  10 . As discussed above, the central hub  126  prevents the ingress of water into the cabinet  12 . 
     Turning now to  FIGS.  10  and  11   , an easy storage aspect of the top panel  14  is shown. Specifically,  FIGS.  10  and  11    are, respectively, perspective and side views showing the top panel  14  removed from the remainder of the cabinet  12  and hanged on the first side panel  18  so that the gas heater  10  can be serviced. As shown in  FIGS.  10  and  11   , the top panel  14  can have one or more hanging devices  146  extending from edges or underside thereof that facilitate hanging the top panel  14  from the first side panel  18  or the second side panel  20 . For example, the hanging devices  146  can be hooks, ledges, blocks, or other suitable geometry to easily hang or removably attach the top panel  14  on the first side panel  18  or the second side panel  20 . The hanging devices  146  can be on a single side of the top panel  14 , or can be on multiple sides. This construction allows a user to perform a majority of repair and service on the internal components of the gas heater  10  by removing the top panel  14 , and conveniently storing the top panel  14  on the cabinet  12  during such repair and service. Specifically, if a user desires to repair or service the gas heater  10 , they can remove the top panel  14  and hang it on one of the first and second side panels  18 ,  20  by the hanging devices  146  so that it lies flush with the first or second side panel  18 ,  20  that it is hung from, thus maintaining the top panel  14  in an easily accessible location. Furthermore, since the multi-conductor cable (not shown) connects the user interface module  16  to the electrical components of the gas heater  10 , the user interface module  16 , which is connected to the top panel  14  as discussed in connection with  FIGS.  8  and  9   , must remain close by. This is made possible by allowing the top panel  14  to be hanged from the first and second side panels  18 ,  20 . 
     Turning to  FIGS.  12 - 14   , the dual junction box  28  is shown in greater detail.  FIG.  12    is a partially exploded elevational view of the gas heater  10  showing the exhaust side panel  22  with the first and second covers  44 ,  46  exploded from the elongated body  44  of the dual junction box  28 .  FIG.  13    is a sectional view of the compact universal gas pool heater taken along Line  13 - 13  of  FIG.  6    showing the interior of the dual junction box  28 . As discussed in detail above in connection with  FIG.  4   , the dual junction box  28  includes the elongated body  42 , the first cover  44 , and the second cover  46 . The first and second open sides  48 ,  50  are on opposite sides of the elongated body  42 , with the first open side  48  providing access to a first chamber  148 , e.g., a low-voltage chamber, and the second open side  50  providing access to a second chamber  150 , e.g., a high-voltage chamber. As discussed above in connection with  FIG.  4   , the first cover  44  can be inserted into, or placed over, the first open side  48  of the elongated body  42  with the locking extension  62  adjacent to and cooperating with the first notch  52 . Thus, when the first cover  44  is inserted into or placed over the elongated body  42  it forms part of the low-voltage chamber  148 . Similarly, the second cover  46  can be inserted into, or placed over, the second open side  50  of the elongated body  42  with the locking extension  64  adjacent to and cooperating with the second notch  54 . Thus, when the second cover  46  is inserted into or placed over the elongated body  42 , it forms part of the high-voltage chamber  150 . 
     The exhaust side panel  22  includes a first wire port  152 , e.g., a low-voltage wire port, and a second wire port  154 , e.g., a high-voltage wire port, that extend therethrough and into the interior of the cabinet  12 . The low-voltage wire port  152  is generally positioned in the low-voltage chamber  148  such that low-voltage wires can extend into the low-voltage chamber  148  from the interior of the cabinet  12 . The high-voltage wire port  154  is generally positioned in the high-voltage chamber  150  such that high-voltage wires can extend into the high-voltage chamber  150  from the interior of the cabinet  12 . As shown in  FIG.  13   , the dual junction box  28  includes an interior wall  156  that separates and isolates the high-voltage chamber  150  from the low-voltage chamber  148 . The interior wall  156  and the elongated body  42  of the dual junction box  28  can be constructed of metal, while the first and second covers  44 ,  46  can be constructed of plastic. 
     Additionally, the exhaust side panel  22  can include first and second slots  158 ,  160  on opposite sides of the elongated body  42 , while the first and second covers  44 ,  46  can have first and second locking protrusions  162 ,  164 , respectively. The first and second locking protrusions  162 ,  164  are configured to be inserted into the first and second slots  158 ,  160  during installation of the first and second covers  44 ,  46 , and prevent the first and second covers  44 ,  46  from being pulled away from the exhaust side panel  22  when installed. 
     As discussed above, when the first and second covers  44 ,  46  are inserted into, or placed over, the elongated body  42 , the locking extension  62  of the first cover  44  cooperates with the first notch  52  of the elongated body  42  to form the first opening  66  (e.g., a low-voltage opening) that accesses the low-voltage chamber  148  of the dual junction box  28 , while the locking extension  64  of the second cover  46  cooperates with the second notch  54  to form the second opening  68  (e.g., a high-voltage opening) that accesses the high-voltage chamber  150  of the dual junction box  28 . The first opening  66  allows for low-voltage electrical cables external to the gas heater  10  to be inserted into the low-voltage chamber  148  of the dual junction box  28  and connected with low-voltage electrical wires internal to the gas heater  10 . The second opening  68  allows for high-voltage electrical cables external to the gas heater  10  to be inserted into the high-voltage chamber  150  of the dual junction box  28  and connected with high-voltage electrical wires internal to the gas heater  10 . 
       FIG.  14    is a partially exploded perspective view of the dual junction box  28  with the second cover  46  exploded and showing installation of a high voltage cable  166 . As shown in  FIG.  14   , to install the high voltage cable  166 , the second cover  46  is removed from the elongated body  42 , thus exposing high-voltage interior wires  168   a ,  168   b  that extend out from the high-voltage wire port  154 . The high-voltage cable  166 , which includes high-voltage exterior wires  170   a ,  170   b , a conduit fitting  172  having a head  174 , a threaded extension  176  extending from the head  174 , and a locking nut  178 , can be temporarily retained by the second notch  54  of the elongated body  42  while the operator connects the wiring. Specifically, the threaded extension  176  can be inserted into the second opening  68  of the second notch  54  such that the head  174  and locking nut  178  of the conduit fitting  172  engage the second notch  54  and thus retain the high-voltage cable  166  in place. This allows an installer to leave the conduit fitting  172  unmounted while making the wire connections within the junction box  28 . The installer can then engage the first high-voltage interior wire  168   a  with the first high-voltage exterior wire  170   a , and engage the second high-voltage interior wire  168   b  with the second high-voltage exterior wire  170   b . Once the wiring is complete, the installer can tighten the nut  178  to secure the conduit fitting  172  to the dual junction box  28 . Alternatively, the nut  178  and head  174  can be close enough together so that the nut  178  need not be tightened to secure the conduit fitting  172  to the dual junction box  28 . Once the conduit fitting  172  is secured to the dual junction box  28 , the installer can then cover the wires with the second cover  46  by inserting the second locking protrusion  164  into the second slot  160  and sliding the second cover  46  into the elongated body  42 . A fastener  180  (e.g., a screw, Christmas tree retainer, etc.) can be inserted through a hole  182  of the elongated body  42  and a hole  184  of the second cover  46  to secure the second cover  46  and the elongated body  42  together. When the second cover  46  is installed, the locking extension  64  of the second cover  46  cooperates with the second notch  54  to form the second opening  68  in which the conduit fitting  172  is mounted, thus retaining the conduit fitting  172 . It should be understood by a person of ordinary skill in the art that a similar installation procedure can be performed for the first cover  44  and associated low-voltage wires. 
     Turning now to  FIGS.  15 ,  16 A, and  16 B , the gas heater  10  is shown in greater detail with the panels  14 ,  18 ,  20 ,  22 ,  24  of the cabinet  12  removed. Specifically,  FIGS.  15 ,  16 A, and  16 B  are, respectively, perspective, side elevational, and top plan views of the compact universal gas pool heater  10  with the panels  14 ,  18 ,  20 ,  22 ,  24  removed showing the internal components housed by the cabinet  12 . The gas heater  10  generally includes the gas inlet pipe  56 , the combustion blower  80 , the air inlet pipe  86 , the tube sheet  91 , a combustion chamber canister  186 , a gas valve  188 , a mount  190  (e.g., an igniter mount), a flame sensor  192 , an igniter  194 , an exhaust pipe  196  mounted to the combustion chamber canister  186 , and a venturi throat  198 . The combustion chamber canister  186  is mounted to the tube sheet  91  on the opposite side to which the water header manifold  90  is mounted. The combustion chamber canister  186  includes legs  200  that support the combustion chamber canister  186  on the base  26 . The mount  190  is secured to the combustion chamber canister  186 , with the flame sensor  192  and igniter  194  mounted thereto and extending therethrough into the combustion chamber canister  186 . The mount  190  is discussed in greater detail below in connection with  FIGS.  27 - 29   . 
     The gas valve  188  generally includes an inlet  202 , a valve body  204 , and an outlet  206 . The inlet  202  of the gas valve  188  is connected with the gas inlet pipe  56 , such that the gas inlet pipe  56  provides gas, e.g., propane or natural gas, to the inlet  202  and thus to the gas valve  188 . The gas valve  188  functions to allow, restrict, and/or prevent the flow of gas from the inlet  202  to the outlet  206 . The outlet  206  of the gas valve  188  is connected with, and provides gas to, the venturi throat  198 , which is in turn connected to the air inlet pipe  86 . The air inlet pipe  86  is connected to a blower inlet  210  of the combustion blower  80 , and provides a mixture of air drawn from atmosphere and gas drawn from the venturi throat  198  to the combustion blower  80 . The venturi throat  198  can be a single gas source venturi throat, or can be configured to switch between multiple gas sources, e.g., propane and natural gas, connected thereto, as disclosed in U.S. Patent Application Publication No. 2018/0038592, the contents of which are hereby incorporated by reference in their entirety. 
     The combustion blower  80  includes the blower inlet  208 , a pump  210 , a mixing chamber  212 , and an outlet  214 . As described above, the air inlet pipe  86  is connected to the blower inlet  208  adjacent the venturi throat  198 , such that a mixture of air and gas is provided to the combustion blower  80  through the blower inlet  208 . The blower inlet  208  is in fluidic communication with the mixing chamber  212  with the air and gas being provided to the mixing chamber  212 . The pump  210  includes a pump impeller (not shown) driven by a motor  216 . The pump impeller is housed within the mixing chamber  212  and rotationally driven by the motor  216 . The pump  210  draws air and gas into the mixing chamber from the air inlet pipe  86  and the venturi throat  198 , mixes the air and gas, and discharges the mixture through the outlet  214  and into the connected gas mixture pipe  82 . The gas mixture pipe  82  is mounted to the tube sheet  91 , and in fluidic communication with the burner  84 , discussed in connection with  FIGS.  22 - 23   . 
       FIGS.  17 - 20    show the gas valve  188  including quick disconnect fittings  218  in greater detail. Specifically,  FIG.  17    is an enlarged view of Area  FIG.  17    of  FIG.  16   .  FIG.  18    is an exploded view of the gas valve  188  showing the gas valve  188  disconnected from the gas inlet pipe  56  and the venturi throat  198 . As shown in  FIGS.  17  and  18   , the inlet  202  of the gas valve  188  can be connected to the gas inlet pipe  56 , e.g., a first component, with a quick disconnect fitting  218 , and the outlet  206  of the gas valve  188  can also be connected to the venturi throat  198 , e.g., a second component, with a quick disconnect fitting  218 . For example, these connections and quick disconnect fittings can be in accordance with the disclosure of U.S. Patent Application Publication No. 2018/0038592, the contents of which are hereby incorporated by reference in their entirety. 
     The inlet  202  of the gas valve  188  can be a piston-style connector  221  that has a cylindrical protrusion  220  including a circumferential recess  222 , a radial o-ring  224  seated in the circumferential recess  222 , and an annular flange  226 . The gas inlet pipe  56  can have an outlet connector  228  that includes an annular flange  230 . The outlet connector  228  of the gas inlet pipe  56  is sized and configured to receive the cylindrical protrusion  220  with the radial o-ring  224  being compressed between an inner wall of the outlet connector  228  and the circumferential recess  222 . When the cylindrical protrusion  220  is fully inserted into the outlet connector  228 , the annular flange  226  of the piston-style connector  221  will be adjacent the annular flange  230  of the outlet connector  228 . The quick disconnect fitting  218  can be clipped over the annular flanges  226 ,  230  to secure the outlet connector  228  and the piston-style connector  221  together. 
       FIG.  19    is a perspective view of the quick disconnect fitting  218 , which includes a body  232 , a first end  234 , and a second end  236 . The quick disconnect fitting  218  can define a substantially C-shaped configuration with the first and second ends  234 ,  236  biased towards each other. The body  232  includes elongated slots  238  extending between the first and second ends  234 ,  236 . The slots  238  can be configured and dimensioned to at least partially receive therein both of the annular flanges  226 ,  230 . In particular, as shown in  FIG.  20   , which is a perspective view of the quick disconnect fitting  218  secured over the annular flanges  226 ,  230  of the piston-style connector  221  and the outlet connector  228 , the quick disconnect fitting  218  can be snapped over the abutting annular flanges  226 ,  230  such that at least a portion of the annular flanges  226 ,  230  extends into and through the slots  238 . Due to the interlocked position of the annular flanges  226 ,  230  relative to the slots  238 , the quick disconnect fitting  218  mechanically retains and prevents separation between the outlet connector  228  (e.g., the gas inlet pipe  56 ) and the piston-style connector  221  (e.g., the gas valve  204 ). 
     Similar to the gas valve inlet  202 , the venturi throat  198  can have a piston-style inlet connector  240  that includes a cylindrical protrusion  242  including a circumferential recess  244 , a radial o-ring  246  seated in the circumferential recess  244 , and an annular flange  248 . The outlet  206  of the gas valve  188  can have an outlet connector  250  that includes an annular flange  252 . The outlet connector  250  of the gas valve  188  is sized and configured to receive the cylindrical protrusion  242  with the radial o-ring  246  being compressed between an inner wall of the outlet connector  250  and the circumferential recess  244 . When the cylindrical protrusion  242  is fully inserted into the outlet connector  250 , the annular flange  248  of the piston-style connector  240  will be adjacent the annular flange  252  of the outlet connector  250 . The quick disconnect fitting  218  can then be clipped over the annular flanges  248 ,  252  such that at least a portion of the annular flanges  248 ,  252  extends into and through the slots  238 . Due to the interlocked position of the annular flanges  248 ,  252  relative to the slots  238 , the quick disconnect fitting  218  mechanically retains and prevents separation between the outlet connector  250  (e.g., the gas valve  204 ) and the piston-style connector  240  (e.g., the venturi throat  198 ). 
     Thus, in view of the above, quick disconnect fittings can be used for both inlet and outlet connections of a gas valve, e.g., between a gas valve and a gas inlet pipe as well as between a gas valve and a venturi throat. This quick disconnect fitting provides an efficient and easy-to-use mechanism for coupling and separating the components of the gas heater  10 , and advantageously eliminates the potential problem of over-torqueing threads when creating a fluid-tight seal between the components of the assembly. 
       FIGS.  21 - 23    are first, second, and third exploded perspective view of the gas heater  10  with the top panel  14  and side panels  18 ,  20 ,  22 ,  24  of the cabinet  12  removed. As described above, the gas heater  10  includes the gas inlet pipe  56 , the combustion blower  80 , the gas mixture pipe  82 , the burner  84 , the air inlet pipe  86 , the water header manifold  90 , the tube sheet  91 , the combustion chamber  186 , the gas valve  188 , the mount  190 , the flame sensor  192 , the igniter  194 , the exhaust pipe  196 , and the venturi throat  198 . In addition to those components, the gas heater  10  also includes a heat exchanger  254 , upper heat exchanger insulation  256 , lower heat exchanger insulation  258 , tube sheet insulation  260 , and a support bracket  262 , all of which are generally covered by and contained within the combustion chamber  186 . 
     The tube sheet  91  is generally disc-shaped with a central body  264  surrounded by a radial flange  266 . The central body  264  includes a central opening  268 , a plurality of inflow tube openings  270 , and a plurality of outflow tube openings  272 , all of which extend through the central body  264  from an exterior side  274  to an interior side  276  thereof. The central opening  268  is configured to have the burner  84  and the gas mixture pipe  82  mounted adjacent thereto, with the burner  84  being mounted on the interior side  276  and the gas mixture pipe  82  being mounted on the exterior side  274 . In this regard, the gas mixture pipe  82  is mounted at a first end to the outlet  214  of the combustion blower  80 , and at a second end to the tube sheet  91  adjacent the central opening  268 . Accordingly, the air/gas mixture that is pumped into the gas mixture pipe  82  by the combustion blower  80  flows through the gas mixture pipe  82 , across the central opening  268  of the tube sheet  91 , and into the burner  84 . 
     The burner  84  includes a cylindrical body  278  having a plurality of radial openings  280 , and a positioning flange  281  that extends radially from a top, e.g., the 12 o&#39;clock position, of the cylindrical body  278  and extends along the longitudinal axis of the cylindrical body  278 . The radial openings  280  allow the air/gas mixture provided to the burner  84  from the gas mixture pipe  82  to dissipate from the burner  84  so that it can be ignited by the igniter  194 , which can be a hot-surface igniter, a spark igniter, a pilot igniter, or a combination thereof. While the positioning flange  281  is shown as extending along the length of the burner  84 , it should be understood that it can be of a smaller length and only extend along a portion of the burner  84  length. 
     The tube sheet insulation  260  is generally disc shaped and dimensioned to cover the central body  264  of the tube sheet  91 . The tube sheet insulation  260  includes a central opening  282 , a plurality of inflow tube openings  284 , and a plurality of outflow tube openings  286 . The central opening  282  of the tube sheet insulation  260  is dimensioned and configured to receive the burner  84  such that the tube sheet insulation  260  can be slid over the burner  84  and abut the tube sheet  91 , with the burner  84  being positioned within the central opening  282  of the tube sheet insulation  260 . Additionally, the plurality of inflow tube openings  284  and the plurality of outflow tube openings  286  of the tube sheet insulation  260  are dimensioned and configured to align with the inflow tube openings  270  and the outflow tube openings  272  of the tube sheet  91  when the tube sheet insulation  260  is positioned adjacent the tube sheet  91 . The tube sheet insulation  260  mitigates the dissipation of heat through the tube sheet  91 , thus forcing heat generated by the gas heater  10  to be absorbed by the heat exchanger  254 . 
     The heat exchanger  254  includes an array of heat exchanger tubes  288 , e.g., seven heat exchanger tubes  288 . The heat exchanger  254  is shown in greater detail in  FIGS.  24 A and  24 B , which are perspective and top plan views of the heat exchanger  254 , respectively. Each of the heat exchanger tubes  288  includes an interior tube  290  surrounded by a plurality of extruded fins  292  on the surface of the interior tube  290 . For the ease of illustration, each individual extruded fin  292  is not shown in  FIGS.  24 A and  24 B , however, the details of the extruded fins  292  are shown in  FIG.  25   . The interior tube  290  includes an inlet  294  and an outlet  296  such that fluid to be heated, e.g., water, can flow into the inlet  294 , through the interior tube  290  and out of the outlet  296 . The heat exchanger tubes  288  are formed in a U-shape, such that the array of heat exchanger tubes  288  define a combustion chamber  297  within which the burner  84  is positioned with the exchanger tubes  288  surrounding the burner  84 . Due to the U-shape configuration, the inlet  294  and the outlet  296  of each heat exchanger tube  288  will be in the same plane P 1  allowing the inlets  294  and the outlets  296  to both be mounted to the tube sheet  91 . Specifically, the inlets  294  of the heat exchanger tubes  288  are dimensioned and configured to be inserted into the inflow tube openings  284  of the tube sheet insulation  260  and the inflow tube openings  270  of the tube sheet  91 , while the outlets  296  of the heat exchanger tubes  88  are dimensioned and configured to be inserted into the outflow tube openings  286  of the tube sheet insulation  260  and the outflow tube openings  272  of the tube sheet  91 . This allows for fluid, e.g., water, to flow across the heat exchanger tubes  288  from the exterior of the tube sheet  91 . This U-shaped design provides a compact construction while providing an optimized heat transfer interface between the burner  84  and the heat exchanger  254 , which reduces the necessary size of the heat exchanger  254  and thus the total size of the gas heater  10 . 
     The extruded fins  292  of the heat exchanger tubes  288 , which are shown in greater detail in  FIG.  25   , are individual elements mounted adjacent to each other on the exterior of the interior tube  290 . The perimeter of each extruded fin  292  includes four bent edges  298  and a single rounded edge  300 . The four bent edges  298  can encompass two-thirds of the total circumference of the extruded fin  292 , while the single rounded edge  300  can encompass one-third of the total circumference of the extruded fin  292 . The bent edges  298  aid in heat transfer, and allow the heat exchanger tubes  288  to be more closely stacked with less space between adjacent heat exchanger tubes  28 . Regarding the heat transfer, the rounded edge  300  allows hot air to enter the extruded fins  292  without disruption, while the bent edges  298  slow the hot air as it passes across the heat exchanger tubes  288  during operation of the gas heater  10 , which increases the heat transferred to the fluid flowing through the interior tubes  290 . 
       FIG.  26 A  is a sectional view taken along Line  26 A- 26 A of  FIG.  16 B , and  FIG.  26 B  is a perspective sectional view taken along Line  26 A- 26 A of  FIG.  16 B .  FIGS.  26 A and  26 B  show the U-shaped design of the heat exchanger  254  and the heat exchanger  254  being supported by the support bracket  262 . 
     As shown in  FIGS.  21 - 23 ,  26 A, and  26 B , the support bracket  262  includes a body  302 , a lower brace  304 , and an upper brace  306 . The lower and upper braces  304 ,  306  extend out from the body  302  and are configured to engage the curved end of the heat exchanger  254  opposite the tube sheet  91 . This engagement secures the heat exchanger  254  to the support bracket  262 . The support bracket  262  rests on the interior wall of the combustion chamber canister  186  and thus supports the otherwise cantilevered heat exchanger  254 . 
     Turning back to  FIGS.  21 - 23   , The upper heat exchanger insulation  256  is positioned on top of the heat exchanger  254 , and the lower heat exchanger insulation  258  is positioned on the bottom of the heat exchanger  254 . The upper and lower heat exchanger insulation  256 ,  258  close off the combustion chamber  297  formed by the heat exchanger tubes  288 . Accordingly, the upper and lower heat exchanger insulation  256 ,  258  reduce heat loss and direct hot gases across the heat exchanger tubes  288  by preventing the hot gasses from dissipating out from the combustion chamber  297  without first passing across the heat exchanger tubes  288 . The upper and lower heat exchanger insulation  256 ,  258  can be secured in place by the support bracket  262 . The upper heat exchanger insulation  256  also includes a cavity  308  defined by walls  310  and an opening  312 . The cavity  308  is dimensioned and configured to receive a portion of the mount  190 . The walls  310  extend into the combustion chamber  297  and include openings  314  that the flame sensor  192  and igniter  194  can extend through and into the combustion chamber  297 . 
     The mount  190  includes a mount body  316 , a mounting flange  318  extending about the perimeter of the canister body  316 , and a spacing flange  320 . The canister body  316  includes a sensor mounting wall  322 , a back wall  324 , and first and second sidewalls  326 ,  328 . The spacing flange  320  can be substantially V-shaped and can extend from the exterior of the sensor mounting wall  322  and/or the back wall  324 . The sensor mounting wall  322  can have a flame sensor mount  330  and an igniter mount  332  (see  FIG.  21   ) mounted thereto, e.g., by screws or other fastening means. The flame sensor mount  330  and the igniter mount  332  can extend through the sensor mounting wall  322 . The flame sensor  192  can extend through and be mounted to the flame sensor mount  330 , e.g., by screws or other fastening means, while the igniter  194  can extend through and be mounted to the igniter mount  332 , e.g., by screws or other fastening means. In some aspects, the spacing flange  320  can extend from the igniter mount  332 . The mount  190  is configured to be at least partially inserted into a top opening  334  of the combustion chamber canister  186 , with a portion of the canister body  316  extending into the interior of the combustion chamber canister  186  and the cavity  308  of the upper heat exchanger insulation  256 , and the mounting flange  318  abutting a gasket  336  that surrounds the top opening  334 . The gasket  336  can be a soft rubber gasket made from, for example, silicone. The mount  190  can be secured to the combustion chamber canister  186  by a plurality of fasteners  336 , thus compressing the gasket  336  between the combustion chamber canister  186  and the mounting flange  318  of the mount  190 . 
     When the body  316  of the mount  190  is inserted into the top opening  334  of the combustion chamber canister  186  and the mount  190  is secured to the combustion chamber canister  186 , the body  316  will be positioned within the cavity  308  of the upper heat exchanger insulation  256 . In this position, the spacing flange  320 , the flame sensor  192 , and the igniter  194  will extend through the upper heat exchanger insulation  256  and into the combustion chamber  297 . This is shown, for example, in  FIGS.  27 - 29   .  FIG.  27    is a sectional view taken along Line  27 - 27  of  FIG.  16 B .  FIG.  28    is a sectional view taken along Line  28 - 28  of  FIG.  16 B .  FIG.  29    is a perspective sectional view taken along Line  28 - 28  of  FIG.  16 B . As can be seen in  FIGS.  27 - 29   , the spacing flange  320 , the flame sensor  192 , and the igniter  194  extend through the upper heat exchanger insulation  256  and into the combustion chamber  297 . The spacing flange  320  engages and interfaces with the positioning flange  281  of the burner  84  such that the positioning flange  281  is seated within the space between first and second legs  338 ,  340  of the spacing flange  320 , thus preventing vertical and lateral movement of the burner  84 , but permitting movement of the burner  84  along its longitudinal axis. The igniter  194 , when mounted with the igniter mount  332 , extends into the combustion chamber canister  186  and is placed at a distance D 1  (see  FIG.  28   ) from the surface of the burner  84  where the radial openings  280  are located and the gas mixture dissipates from. Distance D 1  is the desired spacing distance between the igniter  194  and the burner  84  to achieve efficient and safe ignition of the gas mixture dissipating from the burner  84 . If the distance D 1  is too large, then there may be an excessive explosion accompanies by a loud noise resulting from the ignition of accumulated gas, which is not desirable. For example, distance D 1  can be 0.25″ +/−0.02″. Accordingly, engagement of the positioning flange  281  with the spacing flange  320  allows movement of the burner  84  along the burner&#39;s  84  longitudinal axis, which would not affect the distance D 1  nor the performance of the igniter  194 , but restricts the dimensional spacing between the burner  84  and the igniter mount  332  that would impact the distance D 1  and thus the performance of the igniter  194 . Similarly, the flame sensor  194  is maintained in its position due to being mounted to the flame sensor mount  330  that is tied to the mount  190 . 
     This dimensional consistency is achieved by mounting the igniter mount  332 , the igniter  194 , the flame sensor mount  330 , and the flame sensor  192  to the mount  190 , whose position is tied to the burner  84 , which reduces the number of components that contribute to the “stack-up” of tolerances, as well as allowing the accumulation of tolerance variations to be absorbed by the gasket  336  placed in the gap between the mounting flange  318  of the mount  190  and the combustion chamber canister  186 . That is, the present configuration allows the igniter mount  332  to “bottom out” on the positioning flange  281  through the spacing flange  320 , which ties the igniter mount  332 , and therefore placement of the igniter  194 , to the burner  84 . This limits the number of components that contribute to the stack-up of tolerances to, for example, the height of the positioning flange  281 , the spacing flange  320 , the mount  190 , and the igniter  194 , most of which can vary due to manufacturing. However, each of these tolerance variations is tied together and manifest at the gap between the mounting flange  318  of the mount  190  and the combustion chamber canister  186  where the gasket  336  is placed in order to absorb the tolerances. In furtherance of this, the gasket  336  is designed to be thick enough to absorb the accumulation of tolerance variations in all of the parts. By tying these tolerances together, and permitting the gasket  336  to absorb the accumulation of tolerance variations, the stack-up is essentially reduced to the depth of the igniter mount  332 . 
     In contrast, if the igniter mount  332  was constructed to bottom-out at the connection to the combustion chamber, then it would not be tied to the burner  84  and additional components would contribute to the tolerance variations and overall “stack-up,” which would negatively affect the dimensional consistency between the igniter  194 , the flame sensor  192 , and the burner  84 . In essence, this would result in the tolerance variations being comprised of all tolerance variations relating to the igniter mount  332  in addition to all tolerance variations relating to placement of the burner  84 . However, tying the igniter mount  332  to the burner  84  mitigates this additive consequence. 
     Furthermore, by mounting the igniter mount  332 , the igniter  194 , the flame sensor mount  330 , and the flame sensor  192  to the mount  190 , which is a separate panel from where the burner  84  is mounted, the mount  190  can be placed at a top of the combustion chamber canister  186  so that it can be accessed and serviced from above, e.g., through the top panel  14 . This results in an easier installation and replacement procedure for a servicing technician, while the spacing flange  320  and the positioning flange  281  reduces the dimensional variability. 
     Still further, by having the spacing flange  320  contact the positioning flange  281  of the burner  84 , the heat exchanger  254  including mount  190  can be more easily replaced. Generally, these components are replaced by a technician operating in the blind (e.g., without being able to see where they are positioned). However, in the present aspect, the technician will be able to feel when the spacing flange  320  contacts the positioning flange  281 , and will therefore know that the heat exchanger  254  including mount  190  are in the correct location. 
     In another aspect of the present disclosure, the spacing flange  320  can be a cup, while the positioning flange  281  can be a pin. The cup and pin would function substantially the same as the spacing flange  320  and the positioning flange  281 , respectively, in that they would engage each other to tie the igniter mount  330  to the burner  84 . However, the pin and cup configuration would restrict movement of the burner  84  in three axes as opposed to two with the spacing flange  320  and the positioning flange  281 . 
     As discussed above, by having the igniter  194  and flame sensor  330  mounted to the mount  190 , which is mounted separately from the burner  84  and to a top of the combustion chamber canister  186 , all of the electronics are accessible through the top of the gas heater  10  by removing the top panel  14 . This is in contrast to prior art pool heaters that require a technician to go to multiple sides of the cabinet to service the electronics of the heater. Accordingly, all side panels of such prior art heaters must be accessible, and therefore must be spaced from any adjacent fences, walls of the house or equipment room, etc. In addition to requiring clearance for service, clearance is often needed to prevent the heater from raising the temperature of nearby walls too much. For example, pool heaters will often be spaced 6-18 inches from a nearby wall so as not to increase the temperature of the wall more than is permitted. Accordingly, these clearances serve two purposes: 1) to maintain a suitable low temperature of nearby walls, and 2) to allow a technician access to service the heater. 
     However, the gas heater  10  of the current disclosure allows the electronics and other components to be accessed through the top of the gas heater  10 , and thus the first side panel  18  and the second side panel  20  need not be accessible to a technician. Instead, only the top  12 , the exhaust side panel  22 , and the water header side panel  24  need to be accessible. 
       FIG.  30    is a top plan view of the gas heater  10  with the top panel  14  removed showing the internal components housed by the cabinet  12 , and the relative spacing of these components from the cabinet  12 . In particular, the gas heater  10  is designed with a first gap G 1 , e.g., first internal clearance, between the combustion chamber canister  186  and the first side panel  18 , and a second gap G 2 , e.g., second internal clearance, between the combustion chamber canister  186  and the second side panel  20 . The first gap G 1  can have a first width W 1 , which is the distance between the combustion chamber canister  186  and the first side panel  18 , and the second gap G 2  can have a second width W 2 , which is the distance between the combustion chamber canister  186  and the second side panel  20 . The first and second gaps G 1 , G 2  can be air gaps, or they can be filled with insulation. The gaps G 1 , G 2  reduce the amount of heat transferred to, and thus minimize the temperature of, the first and second side panels  18 ,  20 . Furthermore, heat is removed from the cabinet  12  due to natural convection occurring through the plurality of lower vents  34  and the plurality of upper vents  36  in the exhaust side panel  22 , and the plurality of lower vents  79   a  and the plurality of upper vents  79   b  in the water header side panel  24 , which allow for the circulation of fresh cooler air through the cabinet  12  and particularly across the first and second gaps G 1 , G 2 . This construction allows the gas heater  10  to be installed with very small clearance between the first and second side panels  18 ,  20  and an adjacent fence, wall, or other structure. For example, the gas heater  10  can be installed within 0-6 inches of a nearby wall. 
     Returning to  FIGS.  21 - 23   , the water header manifold  90  can be a single unitary structure or can include multiple components interconnected. The water header manifold  90  can be formed from plastic due to economy of materials and corrosion resistance. For example, the water header manifold can be similar in construction to the disclosure of U.S. Pat. No. 7,971,603, the contents of which are hereby incorporated by reference in their entirety. The water header manifold  90  generally includes an inlet  346 , an inflow tube  348 , an outlet  350 , an outflow tube  352 , a bypass port  354 , a service cartridge housing  356 , a service cartridge  358  (see, e.g.,  FIG.  32   ), and a plurality of mounts  360 . The inflow tube  348  can include a plurality of inflow ports  362  on a rear thereof, while the outflow tube  352  can include a plurality of outflow ports  364 . The inflow ports  362  are dimensioned and configured to match the dimensions and configuration of the inflow tube openings  270  of the tube sheet  91 , and the outflow ports  364  are dimensioned and configured to match the dimensions and configuration of the outflow tube openings  272  of the tube sheet  91 . The water header manifold  90  can be mounted to the tube sheet  91  via the mounts  360  with the inflow ports  362  aligned with the inflow tube openings  270  and the outflow ports  364  aligned with the outflow tube openings  272 , which places the water header manifold in fluidic communication with the heat exchanger tubes  288  of the heat exchanger  254 . 
       FIG.  31    is a sectional view taken along Line  31 - 31  of  FIG.  16 B , generally illustrating the flow path between the water header manifold  90  and the heat exchanger  254 .  FIG.  32    is a sectional view taken along Line  32 - 32  of  FIG.  16 B , generally showing the flow path within the water header manifold  90 . The inflow tube  94  forms an inflow chamber  366 , the outflow tube  352  forms an outflow chamber  368 , and the bypass port  354  forms a bypass chamber  370 . The inlet  346  is in fluidic communication with the inflow chamber  366  such that fluid supplied to the inlet  346  to be heated flows into the inflow chamber  366 , which is in fluidic communication with the inflow ports  362  and the bypass chamber  370 . As shown in  FIG.  31   , the water header manifold  90  is in fluidic communication with the heat exchanger tubes  288 . Particularly, each inflow port  352  is in fluidic communication with a heat exchanger tube inlet  294 , and each outflow port  364  is in fluidic communication with a heat exchanger tube outlet  296 . The outflow chamber  368  is in fluidic communication with the outflow ports  364  and the outlet  350 . Accordingly, fluid flows into the inlet  346  from a pool or spa, into the inflow chamber  366 , through the inflow ports  362 , into the inlet  294  of the heat exchanger tubes  288 , through the heat exchanger tubes  288  where it is heated, out of the outlet  296  of the heat exchanger tubes  288 , through the outflow ports  364 , into the outflow chamber  368 , and out of the outlet  350  back to the pool or spa. The pool or spa water is continuously cycled in this fashion while the gas heater  10  is operational. 
     As noted above, the inflow chamber  366  is in fluidic communication with the bypass chamber  370 . The bypass chamber  370  is capable of being switched into and out of fluidic communication with the outflow chamber  368  by the service cartridge  358 , which includes a pressure valve  372  that opens when the pressure in the bypass chamber  370  is above a predetermined value and closes when the pressure is below a predetermined value. When the pressure valve  372  is open, the inflow chamber  366  is in fluidic communication with the outflow chamber  368  by way of the bypass chamber  370 , which allows a portion of the water to bypass the heat exchanger  254 , resulting in a reduction in pressure in the system. The water header manifold  90 , along with the bypass chamber  370 , service cartridge housing  356 , service cartridge  358 , and associated functionality, can be in accordance with U.S. Pat. No. 7,971,603, the contents of which are hereby incorporated by reference in their entirety. 
       FIGS.  33 - 38    illustrate adaptable aspects of the water header manifold  90  of the present disclosure.  FIGS.  33  and  34    are, respectively, perspective and elevational views of the gas heater  10  without fittings attached. The water header manifold  90  was described in detail in connection with  FIGS.  21 - 23  and  31 - 32    above, which is hereby referenced and need not be repeated. In addition to those components discussed above, e.g., the inlet  346 , the inflow tube  348 , the outlet  350 , the outflow tube  352 , the bypass port  354 , the service cartridge housing  356 , etc., the water header manifold  90  includes one or more inlet mounts  374  (e.g., inlet mounting flanges) adjacent the inlet  346 , and one or more outlet mounts  376  (e.g., outlet mounting flanges) adjacent the outlet  350 . The inlet  346  is positioned at an inlet position, and the outlet  350  is positioned at an outlet position. In this regard, the center of the inlet  346 , along with the inlet mounting flanges  374 , are spaced an inlet height H I  from the bottom of the base  26 , while the center of the outlet  350 , along with the outlet mounting flanges  376 , are spaced an outlet height H O  from the bottom of the base  26 . The inlet height H I  and the outlet height H O  are substantially the same. The inlet  346  and inlet mounting flanges  374  are configured to receive multiple adapters or fittings that can be used to adjust the inlet height H I  and the position of the inlet  346  to match preexisting pool plumbing that was connected to a water inlet of a prior heater that the present gas heater  10  is replacing. Similarly, the outlet  350  and outlet mounting flanges  376  are configured to receive multiple adapters or fittings that can be used to adjust the outlet height H O  and the position of the outlet  350  to match preexisting pool plumbing that was connected to a water outlet of prior heater that the present gas heater  10  is replacing. 
       FIGS.  35  and  36    are, respectively, perspective and elevational views of the gas heater  10  with a first inlet fitting  378  and a first outlet fitting  380  mounted to the water header manifold  90 . The first inlet fitting  378  includes a first inlet fitting inlet  382  and one or more first inlet fitting mounts  384  adjacent the first inlet fitting inlet  382 . Similarly, the first outlet fitting  380  includes a first outlet fitting outlet  386  and one or more first outlet fitting mounts  388  adjacent the first outlet fitting outlet  386 . The first inlet fitting  378  is configured to be secured to the inlet  346  as well as pre-existing pool plumbing without the need for the plumbing to be modified. Similarly, the first outlet fitting  380  is configured to be secured to the outlet  350  as well as pre-existing pool plumbing without the need for the plumbing to be modified. 
     The first inlet fitting  378  can be secured to the inlet  346  of the water header manifold  90  by aligning the first inlet fitting mounts  384  with the inlet mounting flanges  374 . A bolt or other fastening means can then be inserted through the first inlet fitting mounts  384  and the inlet mounting flanges  374  to secure the two together. A gasket can also be provided between the first inlet fitting  378  and the inlet  346  to help maintain pressure and prevent leakage. This places the inlet  346  in fluidic communication with the first inlet fitting inlet  382 . 
     The first outlet fitting  380  can be secured to the outlet  350  of the water header manifold  90  by aligning the first outlet fitting mounts  388  with the outlet mounting flanges  376 . A bolt or other fastening means can then be inserted through the first outlet fitting mounts  388  and the outlet mounting flanges  376  to secure the two together. A gasket can also be provided between the first outlet fitting  380  and the outlet  350  to help maintain pressure and prevent leakage. This places the outlet  350  in fluidic communication with the first outlet fitting outlet  386 . 
     When the first inlet fitting  378  is connected to the inlet  346 , the inlet fitting inlet  382  will be at an adjusted inlet position. In this regard, the first inlet fitting  378  will be positioned at a first inlet fitting height IFH 1  that is the distance between the center of first inlet fitting inlet  382  and the bottom of the base  26 . When the first outlet fitting  380  is connected to the outlet  350 , the outlet fitting outlet  386  will be at an adjusted outlet position. In this regard, the first outlet fitting  380  will be positioned at a first outlet fitting height OM that is the distance between the center of first outlet fitting outlet  386  and the bottom of the base  26 . The first inlet fitting height IFH 1  is the effective height by which the inlet  346  of the water header manifold  90  can be connected to pre-existing pool plumbing and devices. The first outlet fitting height OM is the effective height by which the outlet  350  of the water header manifold  90  can be connected to pre-existing pool plumbing and devices. That is, when the proper inlet and outlet fittings are attached to the water header manifold  90 , the first inlet fitting height IFH 1  should match the height of the pre-existing water inlet plumbing (e.g., that was connected to the prior heater that the present gas heater  10  is replacing) and the first outlet fitting height OM should match the height of the pre-existing water outlet plumbing (e.g., that was connected to the prior heater that the present gas heater  10  is replacing). Accordingly, the pre-existing water inlet plumbing should align with the first inlet fitting inlet  382  such that it can be connected thereto with minimal modification, and the pre-existing water outlet plumbing should align with the first outlet fitting outlet  386  such that it can be connected thereto with minimal modification. This effectively changes the position of the inlet  346  and the outlet  350 . In addition to the first inlet fitting inlet  382  and the first outlet fitting outlet  386  being placed in the proper position for connection, they will also have the same size and fitting type, e.g., connector type, as the prior heater. 
     Essentially, the first inlet fitting  378  adapts the water manifold header  90  inlet  346  to the inlet position of the prior heater that is being replaced, and the first outlet fitting  380  adapts the water manifold header  90  outlet  350  to the outlet position of the prior heater that is being replaced. 
       FIGS.  37  and  38    are, respectively, perspective and elevational views of the gas heater  10  with a second inlet fitting  390  and a second outlet fitting  392  mounted to the water header manifold  90 . The second inlet fitting  390  includes a second inlet fitting inlet  394 , a second inlet fitting body  396 , a second inlet fitting outlet  398 , and one or more second inlet fitting mounts  400 . The second inlet fitting  390  forms a fluidic path between the second inlet fitting inlet  394 , the second inlet fitting body  396 , and the second inlet fitting outlet  398 , such that fluid can flow into the second inlet fitting inlet  394 , across the second inlet fitting body  396 , and out of the second inlet fitting outlet  398 . Similarly, the second outlet fitting  392  includes a second outlet fitting outlet  402 , a second outlet fitting body  404 , a second outlet fitting inlet  406 , and one or more second outlet fitting mounts  408 . The second outlet fitting  392  forms a fluidic path between the second outlet fitting inlet  406 , the second outlet fitting body  404 , and the second outlet fitting outlet  402 , such that fluid can flow into the second outlet fitting inlet  406 , across the second outlet fitting body  404 , and out of the second outlet fitting outlet  402 . The second inlet fitting  390  is configured to be secured to the inlet  346 , as well as pre-existing pool plumbing, without the need for the plumbing to be modified. Similarly, the second outlet fitting  392  is configured to be secured to the outlet  350  as well as pre-existing pool plumbing without the need for the plumbing to be modified. 
     The second inlet fitting  390  can be secured to the inlet  346  of the water header manifold  90  by aligning the second inlet fitting mounts  400  with the inlet mounting flanges  374 . A bolt or other fastening means can then be inserted through the second inlet fitting mounts  400  and the inlet mounting flanges  374  to secure the two together. A gasket can also be provided between the second inlet fitting  390  and the inlet  346  to help maintain pressure and prevent leakage. This places the inlet  346  in fluidic communication with the second inlet fitting inlet  394 . 
     The second outlet fitting  392  can be secured to the outlet  350  of the water header manifold  90  by aligning the second outlet fitting mounts  408  with the outlet mounting flanges  376 . A bolt or other fastening means can then be inserted through the second outlet fitting mounts  408  and the outlet mounting flanges  376  to secure the two together. A gasket can also be provided between the second outlet fitting  392  and the outlet  350  to help maintain pressure and prevent leakage. This places the outlet  350  in fluidic communication with the second outlet fitting outlet  402 . 
     When the second inlet fitting  390  is connected to the inlet  346 , the second inlet fitting inlet  394  will be at an adjusted inlet position while the second inlet fitting outlet  398  will be at the inlet position. In this regard, the second inlet fitting inlet  394  will be positioned at a second inlet fitting height IFH 2  that is the distance between the center of the second inlet fitting inlet  394  and the bottom of the base  26 , and the second inlet fitting outlet  398  will be at the inlet height H I . When the second outlet fitting  392  is connected to the outlet  350 , the second outlet fitting outlet  402  will be at an adjusted outlet position while the second outlet fitting inlet  406  will be at the outlet position. In this regard, the second outlet fitting outlet  402  will be positioned at a second outlet fitting height OFH 2  that is the distance between the center of second outlet fitting outlet  402  and the bottom of the base  26 , and the second outlet fitting inlet  406  will be at the outlet height H O . 
     The second inlet fitting height IFH 2  is the effective height by which the inlet  346  of the water header manifold  90  can be connected to pre-existing pool plumbing and devices. The second outlet fitting height OFH 2  is the effective height by which the outlet  350  of the water header manifold  90  can be connected to pre-existing pool plumbing and devices. That is, when the second inlet fitting  390  and the second outlet fitting  293  are attached to the water header manifold  90 , the second inlet fitting height IFH 2  should match the height of the pre-existing water inlet plumbing (e.g., that was connected to the prior heater that the present gas heater  10  is replacing) and the second outlet fitting height OFH 2  should match the height of the pre-existing water outlet plumbing (e.g., that was connected to the prior heater that the present gas heater  10  is replacing), so long as the second inlet fitting  390  and the second outlet fitting  293  are the proper fittings (e.g., adapters) that match the previous heater. Accordingly, the pre-existing water inlet plumbing should align with the second inlet fitting inlet  394  such that it can be connected thereto with minimal modification, and the pre-existing water outlet plumbing should align with the second outlet fitting outlet  402  such that it can be connected thereto with minimal modification. This effectively changes the position of the inlet  346  and the outlet  350 . In addition to the second inlet fitting inlet  394  and the second outlet fitting outlet  402  being placed in the proper position for connection, they will also have the same size and fitting type, e.g., connector type, as the prior heater. 
     Essentially, the second inlet fitting  390  adapts the water manifold header  90  inlet  346  to the inlet position of the prior heater that is being replaced, and the second outlet fitting  392  adapts the water manifold header  90  outlet  350  to the outlet position of the prior heater that is being replaced. 
     Additionally, although the inlet height measurements H I , IFH 1 , IFH 2  are described as a distance with respect to the bottom of the base  26 , it should be understood that this is only an example and that the inlet height measurements H I , IFH 1 , IFH 2  can be a distance with respect to any reference elevation point that is common to all inlet height measurements H I , IFH 1 , IFH 2 . Similarly, although the outlet height measurements H O , OFH 1 , OFH 2  are described as a distance with respect to the bottom of the base  26 , it should be understood that this is only an example and that the outlet height measurements H O , OFH 1 , OFH 2  can be a distance with respect to any reference elevation point that is common to all outlet height measurements H O , OFH 1 , OFH 2 . 
       FIGS.  39 - 44    show a second heat exchanger  410  according to another aspect of the present disclosure.  FIGS.  39  and  40    are, respectively, perspective and side views of the combustion chamber canister  186  and a second tube sheet  412  housing the second heat exchanger  410 . The second heat exchanger  410  is configured to be incorporated into the gas heater  10  in place of the heat exchanger  254  discussed in connection with  FIGS.  21 - 29   . Accordingly, it should be understood by a person of ordinary skill in the art that the discussion provided above in connection with the gas heater  10 , and the description of the components thereof, hold true for when the second heat exchanger  410  is utilized by the gas heater  10 . As such, for the ease of illustration, a vast majority of those components previously shown and described are not reproduced in  FIGS.  39 - 44   , and the description of those components need not be reproduced, but should be understood to be incorporated. The combustion chamber canister  186  used in combination with the second heat exchanger  410  can be substantially similar in construction to the combustion chamber canister  186  described in connection with  FIGS.  21 - 29   . The second tube sheet  412  is substantially similar in construction to the tube sheet  91  described above in connection with  FIGS.  21 - 29   . The second tube sheet  412  is generally disc-shaped with a central body  414  surrounded by a radial flange  416 . The central body  414  includes a central opening  418  and a plurality of tube openings  420 , half of which are inflow tube openings and half are outflow tube openings. The central opening  418  and the plurality of tube openings  420  extend through the central body  414  from an exterior side  422  to an interior side  424 . The central opening  268  is configured to have the burner  84  and the gas mixture pipe  82  mounted adjacent thereto. In this regard, the gas mixture pipe  82  is mounted to the exterior side  422  of the second tube sheet  412  adjacent the central opening  418 , while the burner  84  is mounted to the interior side  424  of the second tube sheet  412  adjacent the central opening  418 . Accordingly, the air/gas mixture that is pumped into the gas mixture pipe  82  by the combustion blower  80  flows through the gas mixture pipe  82 , across the central opening  418  of the second tube sheet  412 , and into the burner  84 . The combustion chamber canister  186  is mounted to the interior side  424  of the second tube sheet  412  at the radial flange  416  with the second heat exchanger  410  positioned within the combustion chamber canister  186 . The mount  190  can be mounted to the combustion chamber canister  186  as described above in connection with  FIGS.  27 - 29   , along with the igniter  194  and flame sensor  192  mounted thereto. 
       FIGS.  41  and  42    are first and second perspective view of the second heat exchanger  410  mounted to the second tube sheet  412 .  FIGS.  43  and  44    are respectively elevational and perspective sectional views taken along Line  43 - 43  of  FIG.  40   . The second heat exchanger  410  is a semi-circular expanded tube and fin heat exchanger having individual fins organized into a circular pattern to optimize heat transfer in a smaller space. The second heat exchanger  410  includes a plurality of tube-and-fin subassemblies  426  that comprise tubes  428  and a plurality of fins  430 . The tube-and-fin subassemblies  426  are organized into a semi-circular shape around the burner  84  within the combustion chamber canister  186 . The tubes  428  are generally smooth heat exchanger tubes that are bent to form U-shaped “hairpins” and pass through a stack of fins  430 . Each of the tubes  428  includes two open ends  432  that are generally positioned in the same plane, and a curved end  434 . The tubes  428  can extend through the second tube sheet  412  and a front manifold  436 , which has an interior side  438  and an exterior side  440 . In this configuration, the fins  430  are positioned between the interior side  438  of the front manifold  436  and the interior side  424  of the second tube sheet  412 , the curved ends  434  are positioned adjacent the exterior side  440  of the front manifold  436 , and the open ends  432  extend through the tube openings  420  of the second tube sheet  412 . One of the open ends  432  functions as an inlet for water to be heated, and the other of the open ends  432  functions as an outlet for heated water to exit. A water header manifold, e.g., water header manifold  90 , can be mounted to the second tube sheet  412  covering the open ends  432  of the tubes  428  and configured to route water through the tubes  428 . 
     The interior side  424  of the second tube sheet  412  can be lined with a layer of insulation  442  through which the tubes  428  extend to reduce the temperature near a coupled water header manifold. The interior side  438  of the front manifold  436  can also be lined with a layer of insulation  444  that the tubes  428  extend through to prevent the escape of heat and hot gases. Additionally, a layer of combustion chamber insulation  446  fills a top gap in the semi-circular pattern of fins of the heat exchanger  410  which is provided between two of the tube-and-fin subassemblies  426  to allow for placement of the mount  190  and to permit the igniter  194  and flame sensor  192  to reach the burner  84 . The combustion chamber insulation  446  prevents heat and hot gases from escaping through the top gap, thus increasing the efficiency of the heat exchanger  410 . The tube-and-fin subassemblies  426  generally form ⅚ th  of a circle while the combustion chamber insulation  446  and mount  190  fill in the remaining ⅙ th . Forming the tube-and-fin subassemblies  426  in a semi-circle eliminates the need for bottom insulation, and optimizes the transfer of heat in the smallest space possible. 
     The front manifold  436  can additionally include a plurality of radial extensions  447  that are configured to engage and rest on the interior of the combustion chamber canister  186  when the combustion chamber canister  186  is placed over the heat exchanger  410 . Accordingly, the radial extensions  447  support the heat exchanger  410  within the combustion chamber canister  186 . This eliminates the need for a separate support bracket. 
       FIGS.  45  and  46    are perspective and elevational views, respectively, of the fin  430 . Each fin  430  includes a body  448  that includes first and second upper extensions  450 ,  452 , first and second upper gaps  454 ,  456 , first and second lower extensions  458 ,  460 , first and second lower gaps  462 ,  464 , a first sidewall  466 , a second sidewall  468 , and four tube openings  470   a ,  470   b ,  470   c ,  470   d  each surrounded by a collar  472   a ,  472   b ,  472   c ,  472   d . The fin  430  additionally includes a plurality of folded flanges  474  adjacent the first and second upper gaps  454 ,  456 , which form upper channels  476  therebetween. The folded flanges  474  are configured to trap hot gases adjacent the fin  430 , while the upper channels  476  are configured to allow hot gases to flow across the fin  430 . In this regard, the fin  430  is configured to be stacked with other fins  430  along a tube  428 . When stacked on a tube  428 , the folded flanges  474  and the collars  472   a ,  472   b ,  472   c ,  472   d  function to space the fins  430  apart and create a flow path for hot gases between abutting fins  430 . 
     Additionally, the fins  430  are designed so that two fins  430  can be positioned next to each other with the first sidewall  466  of one fin  430  abutting the second sidewall  468  of a second fin  430 , allowing the fins  430  to be arranged in the semi-circle configuration shown in  FIG.  43   . To achieve this semi-circle configuration, the first sidewall  466  is at a first angle θ 1  with respect to the vertical axis, and the second sidewall  468  is at a second angle θ 2  with respect to the vertical axis. To achieve a configuration where six fins  430  complete a full circle, the sum of the first angle θ 1  and the second angle θ 2  will have to total 60°. For example θ 1  and θ 2  can be equal to each other and both be 30°. It should be understood by a person of ordinary skill in the art that the present disclosure contemplates other configurations in which more or less than six fins  430  form a complete circle, and the corresponding angles for θ 1  and θ 2  that would be necessary to achieve a full circle. For example, ten fins  430  could be used in which the sum of θ 1  and θ 2  would equal 36°. Generally, the sum of the first and second angles θ 1  and θ 2  will be equal to three-hundred and sixty (360) divided by the number of tube-and-fin subassemblies  426  required to form a complete circle. 
     Furthermore, the fins  430  are dimensioned and configured so that two or more fins  430  can be nested during manufacturing. In this regard, the first and second lower extensions  458 ,  460  are dimensioned and shaped so as to fit within the first and second upper gaps  454 ,  456 , while the first and second upper extensions  450 ,  452  are dimensioned and shaped so as to fit within the first and second lower gaps  462 ,  464 . This arrangement saves material during manufacturing of the fins  430 . 
       FIGS.  47  and  48    are first and second perspective views illustrating formation of a tube-and-fin subassembly  426 .  FIG.  47    is a perspective view showing two tubes  428  being inserted into a single fin  430 . The tubes  428  have first and second legs  478   a ,  478   b  that extend between the open ends  432  and the curved end  434 . The open ends  432  of a the first tube  428  are inserted into the first tube opening  470   a  and the third tube opening  470   c , while the open ends of the second tube  428  are inserted into the second tube opening  470   b  and the third tube opening  470   d . There is a small clearance between the collars  472   a ,  472   b ,  472   c ,  472   d  and the tubes  428  allowing the fin  430  to be slid along the first and second legs  478   a ,  478   b  toward the curved end  434 . More fins  430  are then added in the same fashion.  FIG.  48    is a perspective view showing two tubes  428  inserted through three fins  430 . This process is repeated until substantially the entire length of the first and second legs  478   a ,  478   b  of the tubes  428  are filled with fins  430  (see  FIG.  42   , for example). Once assembled, the tubes  428  are mechanically expanded to place them in tight contact with the fins  430  so that heat can easily transfer from the fins  430  to the tubes  428 . This mechanical expansion can be accomplished by several different methods, e.g., bullet expansion where a hydraulic machine pushes a round tool through the tube  428  or hydro expansion where a fluid is pressurized inside the tubes  428 . 
     The tube-and-fin subassemblies  426  can have advantages over tubes having extruded fins. Particularly, the tube-and-fin subassemblies  426  are more cost effective at least in part because the fins  430  can be manufactured from a lower-cost metal alloy than the tubes  428 . For example, the tubes  428  can be made of a material that is more robust against damage from pool water, for example, cupronickel, stainless steel, or titanium, while the fins  430  can be made of a material that conducts heat well, but is not as robust though less expensive, for example, copper. 
     During operation, water is continuously routed through the tubes  428  between the open ends  432  by the water header manifold  90 . While water is routed through the tubes  428 , the burner  84  generates a flame from the gas mixture provided thereto. Hot gases generated by the flames then dissipate outward from the combustion chamber  297  and across the fins  430 . As discussed above, the folded flanges  474  of the fins  430  trap the hot gases in contact with the fins  430  and force the hot gases to pass over the tubes  428  and out from the upper channels  476 . The fins  430  capture heat and transfer it to the tubes  428 , which themselves capture heat as well. The tubes  428  transfer the heat to the water flowing therethrough, which exits the tubes into the water header manifold  90  where it is rerouted back to the pool or spa. 
       FIGS.  49 - 50    show an alternative fin  479  that includes flow directors  480 , e.g., louvers, that enhance heat transfer.  FIG.  49    is an elevational view of the alternative fin  479 .  FIG.  50    is a sectional view taken along Line  50 - 50  of  FIG.  49   . Alternative fin  479  is substantially identical in construction to fin  430 , but with the inclusion of flow directors  480  on the body  448 . Accordingly, it should be understood that the alternative fin  479  is constructed in accordance with fin  430 , and such description need not be repeated. Furthermore, elements that are the same between the alternative fin  479  and the fin  430  are labeled with like element numbers. As shown in  FIGS.  45  and  46   , the alternative fin  479  has a plurality of flow directors  480 , e.g., six. The flow directors  480  include a plurality of inclined slats  482  that form a plurality of channels  484  through the body  448  of the alternative fin  479 . The slats  482  force a portion of hot gases through the channels  484  and into contact with adjacent fins  479 . This results in enhanced heat transfer between the hot gases and the alternative fins  479 . While the flow directors  480  are illustrated as louvers in  FIGS.  59  and  50   , it should be understood that other geometries could be used for the flow directors to enhance the transfer of heat. For example, lances, bumps, holes, extrusions, embosses, ribs, and/or other geometry can be included on the body  448  of the alternative fin  479  in addition to or in place of the flow directors  480  to enhance heat transfer. 
       FIGS.  51 - 54    illustrate another exemplary compact universal gas pool heater  510  in accordance with embodiments of the present disclosure. The compact universal gas pool heater  510  shown in  FIGS.  51 - 54    is substantially similar to the compact universal gas pool heater  10  shown in  FIGS.  1 - 4   , and any differences will be discussed in greater detail below. The compact universal gas pool heater  510  (hereinafter “gas heater  510 ”) includes a cabinet  512  having a top panel  514  (e.g., a top), a user interface module  516 , a first side panel  518  (e.g., a first side), a second side panel  520  (e.g., a second side), an exhaust side panel  522  (e.g., an exhaust side or a third side), a water header side panel  524  (e.g., a water header side or a fourth side), and a base  526  (e.g., a bottom). The first side panel  518 , the second side panel  520 , the exhaust side panel  522 , and the water header side panel  524  can generally form a main body of the cabinet  512 . As shown in  FIGS.  51  and  53   , which are, respectively, a first perspective view of the gas heater  510  and an elevational view of the exhaust side panel  522 , the exhaust side panel  522  includes a dual junction box  528 , an exhaust vent  530 , a gas pipe opening  532 , a plurality of lower vents  534 , and a plurality of upper vents  536 . A gas inlet pipe (not shown), such as the gas inlet pipe  56  shown in  FIG.  1   , can extend through the gas pipe opening  532  and into the interior of the cabinet  512  from the exterior where it can connect to a gas valve, for example. 
     The exhaust vent  530  is substantially similar to the exhaust vent  30 , and is generally positioned at, and extends outward from, an upper portion of the exhaust side panel  522 . The exhaust vent  530  includes a body  538  having upper vents  540 , and is configured to receive a portion of an exhaust pipe from the interior of the cabinet  512 , allowing for exhaust fumes to exit the exhaust pipe and dissipate from the gas heater  510  through the top vents  540 . 
     The dual junction box  528  includes an elongated body  542 , a first cover  544 , and a second cover  546 . The elongated body  542  has a first open side  548  (see, e.g.,  FIG.  60   ) and a second open side  550  (see, e.g.,  FIG.  60   ) opposite the first open side  548 . The elongated body  542  also includes a second gas pipe opening  552 , through which a second gas inlet pipe, such as the gas inlet pipe  56  shown in  FIG.  1   , can extend into the interior of the cabinet  512  from the exterior. The two gas pipe openings  532 ,  552  allow for two different sources of gas to be provided to the gas heater  510 . The elongated body  542  also includes first and second holes  554 ,  556  that extend through the elongated body  542 . The first and second holes  554 ,  556  can each include a grommet therein. The holes  554 ,  556  permit wires, electrical conducts, cables, etc., to extend into the dual junction box  528  and connect with high-voltage and low-voltage electrical wires of the gas heater  510 . The first and second covers  544 ,  546  each respectively includes a body  558 ,  560 . The first cover  544  can be inserted into, or placed over, the first open side  548  (see, e.g.,  FIG.  60   ) of the elongated body  542 , while, similarly, the second cover  546  can be inserted into, or placed over, the second open side  550  (see, e.g.,  FIG.  60   ) of the elongated body  542 . The dual junction box  528  is discussed in greater detail in connection with  FIGS.  60 - 62   . 
     As shown in  FIGS.  52  and  54   , which are a second perspective view of the gas heater  510  and an elevational view of the water header side panel  524 , respectively, the water header side panel  524  can include multiple separate panels, including, for example, an upper panel  562 , a first bottom panel  564 , and a second bottom panel  566  defining an opening  568 . The upper panel  562  includes a plurality of upper vents  570 , which allow for exterior air to be drawn into the cabinet  512  and into a combustion blower  572  (see, e.g.,  FIG.  58   ) to be used for combustion. The opening  568  allows for a second water header manifold  574  to extend into the interior of the cabinet  512  and be mounted to a tube sheet  576  (see, e.g.,  FIG.  67   ). The second water header manifold  574  is discussed in greater detail in connection with  FIGS.  79 - 83   . First and second manifold covers  578 ,  580  can be placed over the second water header manifold  574  and secured in place, e.g., to the water header side panel  524  or the second water header manifold  574  itself, in order to cover the second water header manifold  574  and any openings to the cabinet  512 . 
       FIGS.  55 - 57    show the top panel  514  and user interface module  516  in greater detail.  FIG.  55    is an exploded perspective view of the gas heater  510  showing the user interface module  516  separated from the top panel  514 .  FIG.  56    is a partial perspective view of the top panel  514  with the user interface module  516  removed therefrom.  FIG.  57    is a bottom perspective view of the user interface module  516 . The top panel  514  generally includes a first lateral side  582 , a second lateral side  584 , and a central channel  586  that extends substantially the length of the top panel  514  between the first and second lateral sides  582 ,  584 . The central channel  586  can be a recess that extends between the first and second lateral sides  582 ,  584 , and which is sized and configured to receive the user interface module  516 . The user interface module  516  includes an elongated body  588 , first and second sidewalls  590 ,  592 , an electronics housing  594 , a user interface  596 , and a cover  598 . The user interface module  616  is sized and shaped to fit within the central channel  586  of the top panel  514 . 
     According to aspects of the present disclosure, the orientation of the user interface module  516  on the top panel  514  can be reversed in order to suit different installation positions and requirements. As shown in  FIGS.  55  and  56   , the top panel  514  includes an access window  600  positioned within the central channel  586  and surrounded by a perimeter wall  602 . The access window  600  extends through the top panel  514  in to the interior of the cabinet  512 , allowing a user or service technician to access the interior of the cabinet  512  without having to remove the entire top panel  514 . For example, a user or service technician can remove the user interface module  516  in order to access or service the blower  572 , main printed circuit boards (PCBs)  604 , a gas valve  606 , or other components within the cabinet  512 . Additionally, the access window  600  allows for a multi-conductor cable (not shown) to be routed therethrough and connected to the user interface module  516 , thus placing the user interface module  516  in electrical communication with the interior electronics and controls of the gas heater  510 , e.g., the main PCBs  604  which can include one or more controllers. 
     Additionally, the central channel  586  includes a plurality of declined surfaces  608  positioned between the perimeter wall  602  and the first and second lateral sides  582 ,  584 . The declined surfaces  608  decline from a generally central portion of the central channel  586  to the outside of the central channel  586 . The perimeter wall  602  prevents water, e.g., rain water, from flowing into the access window  600  and entering the cabinet  512 , while the declined surfaces  608  direct water toward the perimeter of the top panel  514  to flow outward and off of the top panel  514 , to prevent and/or inhibit pooling. Accordingly, the cabinet  512  is resistant to the entry of water, which it may be exposed to due to the gas heater  510  being located outdoors and in contact with the elements, such as rain and snow. The top panel  514  also includes first and second sets of engagement mechanisms  610 ,  612  (e.g., hooks) on opposite ends of the central channel  586 , along with two fastener mounts  614 . The engagement mechanisms  610 ,  612  and fastener mounts  614  are configured to assist with securing the user interface module  516  to the top panel  514 . While reference is made herein to sets of engagement mechanisms  610 ,  612 , it should be understood that a set could comprise a single engagement mechanism. 
     As shown in  FIG.  57   , the body  588  and sidewalls  590 ,  592  of the user interface module  516  define a cavity  616  that is sized to receive the perimeter wall  602  of the top panel  514  when the user interface module  516  is mounted on the top panel  514 . The cavity  616  allows for the multi-conductor cable extending out from the access window  600  to extend into the electronics housing  594  and electrically connect with the electronics of the user interface module  516  with the main PCBs  604 . Additionally, the sidewalls  590 ,  592  are contoured so as to match the shape of the declined surfaces  608  so that the user interface module  516  lies flush with the top panel  514 . The user interface module  516  additionally includes a fastener hole  618  and a set of user interface engagement mechanisms  620  (e.g., hooks or extensions). The fastener hole  618  is generally positioned adjacent the cover  598  and extends through a curved front wall  622  of the elongated body  588 . When the user interface module  516  is positioned on the top panel  514 , the fastener hole  618  of the user interface module  516  will be aligned with either one of the fastener mounts  614  of the top panel  514  such that a fastener  624 , e.g., a screw, a Christmas tree retainer, etc., can be inserted through the fastener hole  618  and the fastener mount  614  to secure the user interface module  516  to the top panel  514 . The user interface engagement mechanisms  620  extend inward from a curved rear wall  626  of the elongated body  588 , and are sized and shaped to extend into and engage the engagement mechanisms  610 ,  612  of the top panel  514 . 
     To secure the user interface module  516  to the top panel  514 , a user first engages the user interface engagement mechanisms  620  with one set of the engagement mechanisms  610 ,  612 , e.g., the second set of engagement mechanisms  612 , of the top panel  514 . The user then lowers the user interface module  516  into the central channel  586  so that the fastener hole  618  of the user interface module  516  is aligned with the fastener mount  614  of the top panel  514  to prevent the user interface module  516  from longitudinal movement. At this point, the user interface module  516  is positioned between the first and second lateral sides  582 ,  584  of the top panel  514 , which prevent the user interface module  516  from moving laterally. The user then inserts the fastener  624  into the fastener hole  618  and the fastener mount  614  to fully secure the user interface module  516  to the top panel  514 . Specifically, the fastener  624  prevents vertical and rotational movement of the user interface module  516  as well as movement across the channel  586 . At this point, the user interface module  516  is in a first position. To change the orientation of the user interface module  516  to a second position, a user removes the fastener  624 , lifts the user interface module  516  vertically off of the top panel  514 , and rotates the user interface module  516  one-hundred and eighty (180) degrees about central axis B. The user then repeats the steps for securing the user interface module  516  to the top panel  514 , but instead of placing the user interface engagement mechanisms  620  in the second set of engagement mechanisms  612 , the user interface engagement mechanisms  620  are engaged with the first set of engagement mechanisms  610 . The user then lowers the user interface module  516  until it rests in the central channel  586 , and inserts the fastener  624  into the fastener hole  618  and the fastener mount  614  to fully secure the user interface module  516  to the top panel  514 . Thus, the user interface module  516  can be placed in two different configurations that are one-hundred and eighty (180) degrees opposite of each other without requiring the entire top panel  514  to be removed and rotated. That is, in the first position, the user interface  596  of the user interface module  516  is easily accessible by a user standing at the first side panel  518  of the cabinet  512 , while in the second position the user interface  596  of the user interface module  516  is easily accessible by a user standing at the second side panel  520  of the cabinet  512 . 
     When the user interface module  516  is secured to the top panel  514 , the top portion of the elongated body  588  lies flush with first and second lateral sides  582 ,  584  of the top panel  514 . However, the fit between the user interface module  516  and the first and second lateral sides  582 ,  584  of the top panel  514  need not be a rain-proof seal, instead a small gap can be provided that allows for water, e.g., rain water, to flow around and below the user interface module  516 , where it is channeled to the edges of the top panel  514  and runs off the gas heater  510 . As discussed above, the perimeter wall  602  and declined surfaces  608  prevent the ingress of water into the cabinet  612 . 
       FIGS.  58  and  59    show the interior of the gas heater  510  in greater detail. Specifically,  FIGS.  58  and  59    are, respectively, partial perspective and top plan views of the gas heater  510  with the top panel  514  removed showing the internal components housed by the cabinet  512 . As shown in  FIGS.  58  and  59   , the cabinet  512  of the gas heater  510  generally houses the combustion blower  572 , the second water header manifold  574  (at least partially), the tube sheet  576 , the main PCBs  604 , the gas valve  606 , a transformer  628 , a blower vacuum switch  630 , a control panel  632  mounted to the interior of the exhaust side panel  522  and supporting the main PCBs  604 , a burner  634 , a combustion chamber enclosure  636  (e.g., a combustion chamber), an igniter  638 , a flame sensor  640 , an exhaust pipe  642  mounted to the combustion chamber enclosure  636 , and a gas pipe  644  extending from an outlet of the gas valve  606  to the combustion blower  572 . The combustion chamber enclosure  636  is mounted to the tube sheet  576  adjacent the second water header manifold  574 , which is discussed in greater detail below. The igniter  638  and the flame sensor  640  are mounted to the combustion chamber enclosure  636  by mounts  646 ,  648  adjacent the burner  634  and extend into the combustion chamber enclosure  636 , which is discussed in greater detail below. It should be understood that the gas valve  606  can be substantially similar in construction and functionality to gas valve  188  shown and described, for example, in  FIGS.  16 A- 18   , and which description need not be repeated. Additionally, while a gas inlet pipe is not shown connected to the gas valve  606 , it should be understood that a gas inlet pipe, such as the gas inlet pipe  56  shown in  FIGS.  16 A- 18   , could be connected to the gas valve  606  to provide gas thereto. 
     It should also be understood that the combustion blower  572  can be substantially similar in construction and functionality to the combustion blower  80  shown and described, for example, in  FIGS.  15 - 16 B . The combustion blower  572  includes a blower inlet  650 , a pump  652 , a mixing chamber  654 , and an outlet  656 . Air can be drawn into the combustion blower  572  through the blower inlet  650 . The gas pipe  644 , which extends from the outlet of the gas valve  606 , connects to the combustion blower  572  at the blower inlet  650  such that a mixture of air and gas is provided to the combustion blower  572 . The combustion blower  572  can also include a venturi throat (not shown) such as the venturi throat  198  shown in  FIG.  16 B . The blower inlet  650  is in fluidic communication with the mixing chamber  654  with the air and gas being provided to the mixing chamber  654 . The pump  652  includes a pump impeller (not shown) driven by a motor  658 . The pump impeller is housed within the mixing chamber  654  and rotationally driven by the motor  658 . The pump  652  draws air and gas into the mixing chamber  654  from the air inlet pipe  650  and the gas pipe  644 , mixes the air and gas, and discharges the mixture through the outlet  656  and into the connected burner  634 , discussed in connection with  FIGS.  67 - 68   . 
     Turning to  FIGS.  60 - 62   , the dual junction box  528  is shown in greater detail. It is noted that the dual junction box  528  can be similar in construction to the dual junction box  28  shown and described in connection with  FIGS.  12 - 14   .  FIG.  60    is a partially exploded elevational view of the gas heater  510  showing the exhaust side panel  522  with the first and second covers  544 ,  546  exploded from the elongated body  542  of the dual junction box  528 .  FIG.  61    is a sectional view of the compact universal gas pool heater  510  taken along line  61 - 61  of  FIG.  59    showing the interior of the dual junction box  528 . As discussed in detail above in connection with  FIGS.  51  and  53   , the dual junction box  528  includes the elongated body  542 , the first cover  544 , and the second cover  546 . The first and second open sides  548 ,  550  are on opposite sides of the elongated body  542 , with the first open side  548  providing access to a first chamber  660 , e.g., a low-voltage chamber, and the second open side  550  providing access to a second chamber  662 , e.g., a high-voltage chamber. As discussed above in connection with  FIGS.  51  and  53   , the first cover  44  can be inserted into, or placed over, the first open side  548  of the elongated body  542 . Thus, when the first cover  544  is inserted into or placed over the elongated body  542 . it can form part of the low-voltage chamber  660 . Similarly, the second cover  546  can be inserted into, or placed over, the second open side  550  of the elongated body  542 . Thus, when the second cover  546  is inserted into or placed over the elongated body  542  it can form part of the high-voltage chamber  662 . 
     The exhaust side panel  522  includes a first wire port  664 , e.g., a low-voltage wire port, and a second wire port  666 , e.g., a high-voltage wire port, that extend therethrough and into the interior of the cabinet  512 . The low-voltage wire port  664  is generally positioned in the low-voltage chamber  660  such that low-voltage wires can extend into the low-voltage chamber  660  from the interior of the cabinet  512 . The high-voltage wire port  666  is generally positioned in the high-voltage chamber  662  such that high-voltage wires can extend into the high-voltage chamber  662  from the interior of the cabinet  512 . As shown in  FIG.  61   , the dual junction box  528  includes interior walls  668 ,  670  that separate and isolate the low-voltage chamber  660  and the high-voltage chamber  662 . The interior walls  668 ,  670  and the elongated body  542  of the dual junction box  528  can be constructed of metal, while the first and second covers  544 ,  546  can be constructed of plastic. 
     Additionally, the first and second covers  544 ,  546  are configured to removably engage the exhaust side panel  522  through an engagement mechanism. Specifically, the exhaust side panel  522  can include first and second sets of slots  672 ,  674  on opposite sides of the elongated body  542 , while the first and second covers  544 ,  546  can each have one or more locking protrusions  676 ,  678 , respectively. The locking protrusions  676 ,  678  are configured to be inserted into the first and second sets of slots  672 ,  674  during installation of the first and second covers  544 ,  546 , and prevent movement of the first and second covers  544 ,  546  when installed. 
     As discussed above, when the first and second covers  544 ,  546  are inserted into, or placed over, the elongated body  542 , they respectively cover the first and second open sides  548 ,  550  of the elongated body  542 , and isolate the low-voltage chamber  660  and the high-voltage chamber  662 . The first hole  554  allows for low-voltage electrical cables external to the gas heater  510  to be inserted into the low-voltage chamber  660  of the dual junction box  528  and connected with low-voltage electrical wires internal to the gas heater  510 . The second hole  556  allows for high-voltage electrical cables external to the gas heater  510  to be inserted into the high-voltage chamber  662  of the dual junction box  528  and connected with high-voltage electrical wires internal to the gas heater  510 . 
       FIG.  62    is a partially exploded perspective view of the dual junction box  528  with the second cover  546  exploded and showing installation of a high voltage cable  682 . As shown in  FIG.  62   , to install the high voltage cable  682  the second cover  546  is removed from the elongated body  542 , thus exposing high-voltage interior wires  684   a ,  684   b  that extend out from the high-voltage wire port  666 . The high-voltage cable  682 , which includes high-voltage exterior wires  686   a ,  686   b , can extended through and be retained by the second hole  556  of the elongated body  542 . Once an installer connects the high-voltage interior wires  684   a ,  684   b  with the high-voltage exterior wires  686   a ,  686   b  and wiring is complete, the installer can cover the wire connection with the second cover  546  by inserting the locking protrusions  678  into the slots  674  and placing the second cover  546  over the elongated body  542 . A fastener  688  (e.g., a screw, Christmas tree retainer, etc.) can be inserted through a hole  690  of the second cover  546  and a hole  692  of the elongated body  542  to secure the second cover  546  and the elongated body  542  together. It should be understood by a person of ordinary skill in the art that a similar installation procedure can be performed for the first cover  544  and associated low-voltage wires. It should be understood to those skilled in the art that any reference herein to cable, wire, cord, etc., encompasses any cable, wire, cord, or conductor known in the art capable of conducting electricity, conducting power, and/or transferring signals (e.g., control signals). 
     Turning now to  FIGS.  63 - 65   , the gas heater  510  is shown in greater detail with the panels  514 ,  518 ,  520 ,  522 ,  524  of the cabinet  512  removed. As discussed above in connection with  FIGS.  58  and  59   , the gas heater  510  generally includes the combustion blower  572 , the second water header manifold  574 , the tube sheet  576 , the main PCBs  604 , the gas valve  606 , the transformer  628 , the blower vacuum switch  630 , the control panel  632 , the burner  634 , the combustion chamber enclosure  636 , the igniter  638 , the flame sensor  640 , the exhaust pipe  642 , and the gas pipe  644 . The main PCBs  604 , the transformer  628 , and the blower vacuum switch  630  can be mounted to the control panel  632 , and positioned so as to be easily accessible through the access window  600  of the top panel  514 , as discussed in connection with  FIGS.  55  and  56   . Additionally, the combustion chamber enclosure  636  can include legs  694  that support the combustion chamber enclosure  636  on the base  526 . 
       FIGS.  66 - 68    are first, second, and third exploded perspective view of the gas heater  510  with the top panel  514  and side panels  518 ,  520 ,  522 ,  524  of the cabinet  512  removed. In addition to those components previously enumerated and described, the gas heater  510  also includes a third heat exchanger  696 , tube sheet insulation  698 , front heat exchanger insulation  700 , and a front manifold  702 , all of which are generally covered by and contained within the combustion chamber enclosure  636 . It should be understood that various combinations of components of the gas heater  510  contained within the cabinet  512  can form a heater subassembly. For example, the combustion chamber enclosure  636 , the third heat exchanger  696 , the burner  634 , and the main PCBs  604  might be referred to as a heater subassembly. However, more or less components may be included in the heater subassembly. 
     The tube sheet  576  can be square-shaped with a central body  704  surrounded by a perimeter flange  706 . The central body  704  includes a plurality of tube openings  708  that extend through the central body  704  between an exterior side  710  to an interior side  712  thereof. The tube sheet insulation  698  is generally square-shaped and dimensioned to cover the central body  704  of the tube sheet  576 . The tube sheet insulation  698  includes a plurality of tube openings  714 , which are dimensioned and configured to align with the tube openings  708  of the tube sheet  576  when the tube sheet insulation  698  is positioned adjacent the tube sheet  576 . The tube sheet insulation  698  mitigates the dissipation of heat through the tube sheet  576 , thus forcing heat generated by the gas heater  510  to be absorbed by the third heat exchanger  696 . 
     The third heat exchanger  696  can be similar in construction to the second heat exchanger  410  shown in, and described in connection with,  FIGS.  41 - 44   . The third heat exchanger  696  is shown in greater detail in  FIGS.  69 - 72   , which are perspective, top plan, front elevational, and rear elevational views of the third heat exchanger  696 , respectively. The third heat exchanger  696  is a semi-circular expanded tube-and-fin heat exchanger that has individual fins organized into a semi-circular or circular pattern to optimize heat transfer in a smaller space. The third heat exchanger  696  includes a plurality of tube-and-fin subassemblies  716 , e.g., three, that each comprises three tubes  718  and a plurality of fins  720 . For the ease of illustration, each individual fin  720  is not shown in  FIGS.  67 - 72   , however, the details of the fins  720  are shown in  FIGS.  73 - 74   . The tube-and-fin subassemblies  716  are organized into a semi-circular shape within the combustion chamber enclosure  636 . The tubes  718  are generally smooth heat exchanger tubes that are bent to form U-shaped “hairpins” and pass through a stack of fins  720 . Each of the tubes  718  includes two open ends  722  that are generally positioned in the same plane, and a curved end  724 . The tubes  718  can extend through the tube sheet  576 , the front heat exchanger insulation  700 , and the front manifold  702 , which has an interior side  726 , an exterior side  728 , and a plurality of tube openings  729 , half of which are inflow tube openings and half are outflow tube openings. The tube openings  729  extend through the front manifold  702  from the exterior side  728  to the interior side  726 . In this configuration, the fins  720  are positioned between the interior side  726  of the front manifold  702  and the interior side  712  of the tube sheet  576 , the curved ends  724  are positioned adjacent the exterior side  728  of the front manifold  702 , and the open ends  722  extend through the tube openings  708  of the tube sheet  576 . For each tube  718 , one of the open ends  722  functions as an inlet for water to be heated, and the other of the open ends  722  functions as an outlet for heated water to exit. The second water header manifold  574  can be mounted to the tube sheet  576  covering the open ends  722  of the tubes  718  and configured to route water through the tubes  718 , which is discussed in greater detail in connection with  FIGS.  79 - 83   . 
     As previously noted, the interior side  712  of the tube sheet  576  can be lined with the tube sheet insulation  698  which includes a plurality of tube openings  714  that the tubes  718  can extend through. The tube sheet insulation  698  functions to reduce the temperature near the coupled water header manifold  574 . The interior side  726  of the front manifold  702  can be lined with the front heat exchanger insulation  700 , which includes a plurality of tube openings  730  that the tubes  718  extend through to prevent the escape of heat and hot gases. Forming the tube-and-fin subassemblies  716  in a semi-circle eliminates the need for bottom insulation, and optimizes the transfer of heat in the smallest space possible. 
     The front manifold  702  can additionally include a bottom extension  732  that is configured to engage and rest on the interior of the combustion chamber enclosure  636  when the combustion chamber enclosure  636  is placed over the heat exchanger  696 . Accordingly, the bottom extension  732  supports the heat exchanger  696  within the combustion chamber enclosure  636 . This eliminates the need for a separate support bracket. 
     Turning to  FIGS.  73 - 76   , the fins  720  are shown in greater detail in  FIGS.  73  and  74   , while formation of the tube-and-fin subassemblies is shown in  FIGS.  75  and  76   . Specifically,  FIGS.  73  and  74    are perspective and elevational views, respectively, of the fin  720 . The fin  720  is similar to the fin  420  illustrated in  FIGS.  45 - 46   , but includes three tube openings  734   a ,  734   b ,  734   c  instead of four, among other differences. Each fin  720  includes a body  736  that includes first and second upper extensions  738 ,  740 , an upper gap  742 , a lower extension  744 , first and second lower gaps  746 ,  748 , and the three tube openings  734   a ,  734   b ,  734   c  that are each surrounded by a collar  750   a ,  750   b ,  750   c . The fin  720  additionally includes a plurality of folded flanges  752  adjacent the first and second upper gaps  738 ,  740 , which form upper channels  754  therebetween. The folded flanges  752  are configured to trap hot gases adjacent the fin  720 , while the upper channels  754  are configured to allow hot gases to flow across the fin  720 . In this regard, the fin  720  is configured to be stacked with other fins  720  along a tube  718 . When stacked on a tube  718 , the folded flanges  752  and the collars  750   a ,  750   b ,  750   c  function to space the fins  720  apart and create a flow path for hot gases between abutting fins  720 . 
     Additionally, the fins  720  are designed so that two fins  720  can be positioned next to each other with a first side  756  of one fin  720  abutting a second side  758  of a second fin  720 , allowing the fins  720  to be arranged in the semi-circle configuration shown in  FIGS.  69 - 72   . To achieve this semi-circle configuration, the first side  756  can be at an angle θ 3  with respect to the vertical axis, and the second side  758  can be set at an angle θ 4  with respect to the vertical axis, as shown in  FIG.  74   . To achieve a configuration where six fins  430  complete a full circle, the sum of the angle θ 3  and the angle θ 4  will have to total 60°. For example θ 3  and θ 4  can be equal to each other and both be 30°. It should be understood by a person of ordinary skill in the art that the present disclosure contemplates other configurations in which more or less than six fins  720  form a complete circle, and the corresponding angles for θ 3  and θ 4  that would be necessary to achieve a full circle. For example, ten fins  720  could be used in which the sum of θ 3  and θ 4  would equal 36°. Generally, the sum of the angles θ 3  and θ 4  will be equal to three-hundred and sixty (360) divided by the number of tube-and-fin subassemblies  716  required to form a complete circle. However, it is also contemplated that the fins  720  can be configured so as to not form a complete circle, but instead designed to leave a space of a desired size, e.g., a top gap  760 , between two of the tube-and-fin subassemblies  716  (see  FIGS.  69 - 72   ), which can be positioned adjacent the burner  634  and receive a portion of a burner (e.g., the burner  774  shown and described in connection with  FIGS.  84 - 87   ) or gas. 
     Furthermore, the fins  720  are dimensioned and configured so that two or more fins  720  can be nested during manufacturing. In this regard, the upper gap  742  can be dimensioned and shaped so as to fit into the lower extension  744 , while the upper extensions  738 ,  740  can be dimensioned and shaped so as to fit into the first and second lower gaps  746 ,  748 . This arrangement saves material during manufacturing of the fins  720 . 
       FIGS.  75  and  76    are first and second perspective views illustrating formation of a tube-and-fin subassembly  716 .  FIG.  75    is a perspective view showing three tubes  718  being inserted into two fins  720 . The tubes  718  have first and second legs  762   a ,  762   b  that extend between the open ends  722  and the curved end  724 . The open ends  722  of the first tube  718  are inserted into the first tube opening  734   a  and the third tube opening  734   c  of the first of the two fins  720 , the open ends  722  of the second tube  718  are inserted into the first tube opening  734   a  and the third tube opening  734   c  of the second of the two fins  720 , and the open ends  722  of the third tube  718  are inserted into the second tube opening  734   b  of the first of the two fins  720  and the second tube opening  734   b  of the second of the two fins  720 . There is a small clearance between the collars  750   a ,  750   b ,  750   c  and the tubes  718  allowing the fins  720  to be slid along the first and second legs  762   a ,  762   b  toward the curved ends  724 . More fins  720  are then added in the same fashion. In this configuration, two fins  720  are linked by one of the three tubes  718 , which provides for added support and rigidity of each tube-and-fin subassembly  716 .  FIG.  75    is a perspective view showing three tubes  718  inserted through six fins  720 . This process is repeated until substantially the entire length of the first and second legs  762   a ,  762   b  of the tubes  718  are filled with fins  720  (see  FIG.  69   , for example). Once assembled, the tubes  718  are mechanically expanded to place them in tight contact with the fins  720  so that heat can easily transfer from the fins  720  to the tubes  718 . This mechanical expansion can be accomplished by several different methods, e.g., bullet expansion where a hydraulic machine pushes a round tool through the tubes  718  or hydro expansion where a fluid is pressurized inside the tubes  718 . 
     The tube-and-fin subassemblies  716  can have advantages over tubes having extruded fins. Particularly, the tube-and-fin subassemblies  716  are more cost effective at least in part because the fins  720  can be manufactured from a lower-cost metal alloy than the tubes  718 . For example, the tubes  718  can be made of a material that is more robust against damage from pool water, for example, cupronickel, stainless steel, or titanium, while the fins  720  can be made of a material that conducts heat well, but is not as robust though less expensive, for example, copper. 
     During operation, water is continuously routed through the tubes  718  between the open ends  722  by the second water header manifold  574 . While water is routed through the tubes  718 , the burner  634  generates a flame from the gas mixture provided thereto. Hot gases generated by the flames then dissipate outward across the fins  720 . As discussed above, the folded flanges  752  of the fins  720  trap the hot gases in contact with the fins  720  and force the hot gases to pass over the tubes  718  and out from the upper channels  754 . The fins  720  capture heat and transfer it to the tubes  718 , which themselves capture heat as well. The tubes  718  transfer the heat to the water flowing therethrough, which exits the tubes into the second water header manifold  574  where it is ultimately rerouted back to the pool or spa. 
     Turning back to  FIGS.  67  and  68   , in one aspect, the burner  634  can include an upper mounting plate  764  and a lower discharge mesh plate  766  positioned below the upper mounting plate  764 . The upper mounting plate  764  includes a central opening  768  (e.g., a gas opening), a tapered body  770 , and a perimeter flange  772  that extends about the perimeter of the tapered body  770 . The lower discharge mesh plate  766  is shown as being a solid component for the ease of illustration, but should be understood to be a mesh or perforated element that allows for the dissipation of the air/gas mixture provided to the burner  634 , discussed below. The burner  634  can be mounted to the combustion chamber enclosure  636  by way of the perimeter flange  772 , while the outlet  656  of the combustion blower  572  can be mounted about the central opening  768  of the upper mounting plate  764 . This configuration allows for the air/gas mixture discharged from the outlet  656  of the combustion blower  572  to flow into the burner  634  through the central opening  768 . The air/gas mixture is then dissipated from the lower discharge mesh plate  766  into the combustion chamber canister  636  to be ignited by the igniter  638  (e.g., a hot-surface igniter, a spark igniter, a pilot igniter, or a combination thereof), which is discussed in greater detail in connection with  FIGS.  77  and  78   . The burner  634  can also include a distributor plate (not shown) internal thereto adjacent the central opening  768 , which functions to evenly distribute the air/gas mixture provided by the combustion blower  572  to the burner  634  allowing for a normalized ignition of the air/gas mixture. It should be understood that while the burner  634  is shown as a substantially “flat” configuration in  FIGS.  67  and  68   , the burner can be a “box”-shaped burner, such as the burner  774  shown and described in connection with  FIGS.  84 - 87    that extends into the combustion chamber enclosure  636 . That is, it should be understood that the burner  634  shown in  FIGS.  67 - 68    and the burner  774  shown in  FIGS.  84 - 87    are for the most part interchangeable based on a user&#39;s desired configuration. 
     The combustion chamber enclosure  636  can include a first sidewall  776   a , a second sidewall  776   b , a front  776   c , a chamfered wall  776   d , a top  776   e , a bottom  776   f , and a rear mounting flange  776   g  surrounding a rear opening  778 . However, it should be understood that other configurations of the combustion chamber enclosure  636  are contemplated by the present enclosure. The top  776   e  can include a burner opening  780  surrounded by a gasket  782 . The burner opening  780  is configured to receive a portion of the burner  634 ,  774 , e.g., a portion of the lower discharge mesh plate  766  can extend through the burner opening  780  and into a combustion chamber cavity  784  defined by the combustion chamber enclosure  636 . This configuration allows for the air/gas mixture dissipated by the lower discharge mesh plate  766  to dissipate into the combustion chamber cavity  784  of the combustion chamber enclosure  636  and be ignited by the igniter  638 . The heat exchanger  696  can be positioned within the combustion chamber cavity  784  of the combustion chamber enclosure  636 , while the tube sheet  576  can be secured to the rear mounting flange  776   g  to secure the heat exchanger  696  and the second water header manifold  574  to the combustion chamber enclosure  636  with the bottom extension  732  of the front manifold  702  resting on the bottom  776   f  and supporting the heat exchanger  696 . The tube sheet  576  functions as the back of the combustion chamber enclosure  636  and seals the combustion chamber cavity  784 . Additionally, the perimeter flange  772  of the burner&#39;s upper mounting plate  764  can rest on the gasket  782  and create a seal therewith to prevent any portion of the air/gas mixture from escaping the combustion chamber enclosure  636 . The top  776   e  can also include a mounting section  786  adjacent the burner opening  780  which the igniter  638  and flame sensor  640  can be mounted to and extend into the combustion chamber cavity  784  of the combustion chamber enclosure  636 . This is shown, for example, in  FIGS.  77  and  78   . Alternatively, the mounting section  786  can be positioned on the burner  634 , e.g., on the perimeter flange  772  of the burner&#39;s upper mounting plate  764 , so that the igniter  638  and the flame sensor  640  are directly mounted to, and interlocked with, the burner  634 . 
       FIG.  77    is a sectional view taken along Line  77 - 77  of  FIG.  65   .  FIG.  78    is a perspective sectional view taken along Line  77 - 77  of  FIG.  65   . As can be seen in  FIGS.  77  and  78   , the burner  634  can be mounted adjacent the burner opening  780  of the combustion chamber enclosure  636  such that the lower discharge mesh plate  766  is positioned over the burner opening  780 . Additionally, the lower discharge mesh plate  766  can extend at least partially into the burner opening  780 . The lower discharge mesh plate  766  is configured to dissipate the air/gas mixture provided thereto by the combustion blower  572  into a combustion region  788  within the combustion chamber cavity  784  of the combustion chamber enclosure  636 . The combustion region  788  is generally in the center of the heat exchanger  696  and surrounded by the tube-and-fin subassemblies  716  thereof. This configuration forces hot gas created due to combustion of the air/gas mixture to dissipate outward through the heat exchanger  696  and across the fins  720  of the heat exchanger  696 , thus allowing the fins  720  to absorb heat from the hot gas, transfer the heat absorbed to the tubes  718 , and into the water being circulated through the tubes  718 . Furthermore, the box-shaped configuration of the combustion chamber enclosure  636  allows for lower pockets  790  within the combustion chamber cavity  784  of the combustion chamber enclosure  636  exterior to the heat exchanger  696 . The lower pockets  790  can have baffles (not shown) positioned therein, which can evenly distribute hot gas that has passed across the heat exchanger  696  and into the lower pockets  790 . Additionally, the baffles (not shown) can force the hot gas that has passed into the lower pockets  790  back upward and through the heat exchanger  696  a second time, which allows for additional heat to be extracted and increases efficiency of the heat exchanger  696 . 
     Moreover, as referenced above, the igniter  638  and the flame sensor  640  can be mounted to the mounting section  786  adjacent the burner opening  780  so as to extend vertically into the combustion region  788  of the combustion chamber enclosure  636 . The front heat exchanger insulation  700  can include first and second cutouts  792 ,  794  configured to receive the igniter  638  and the flame sensor  640 . When the igniter  638  and the flame sensor  640  are mounted to the mounting section  786 , and the burner  634  is mounted to the combustion chamber enclosure  636  adjacent the burner opening  780 , the igniter  638  and the flame sensor  640  will be at a pre-set desired distance from the lower discharge mesh plate  766  from which the air/gas mixture is dissipated. This distance is the desired distance to achieve efficient and safe ignition of the air/gas mixture dissipated from the burner  634 . If the distance is too large then there may be an excessive explosion accompanied by a loud noise resulting from the ignition of accumulated gas, which is not desirable. Accordingly, it is desired to maintain the distance between the igniter  638  and the lower discharge mesh plate  766  as constant. This dimensional consistency is achieved by mounting both the igniter  638  (and the flame sensor  640 ) and the burner  634  to the top  776   e  of the combustion chamber enclosure  636 , or by mounting both the igniter  638  (and the flame sensor  640 ) directly to the burner  634 , which drastically reduces the number of components that contribute to the “stack-up” of tolerances. In essence, this reduces the tolerance stack to the hole through which the igniter  638  extends. Additionally, by mounting the igniter  638 , the flame sensor  640 , and the burner  634  to the top  776   e  of the combustion chamber enclosure  636 , each of these components can be accessed and serviced from above, e.g., through the top panel  514  or through the access window  600  that extends through the top panel  514 . This results in an easier installation and replacement procedure for a servicing technician. 
     Alternatively, the igniter  638  and/or the flame sensor  640  can be mounted to the tube sheet  576  at a position adjacent the burner  634  near the top of the tube sheet  576 , e.g., at a position that is above the water manifold header  574  and between the water manifold header  574  and the top of the tube sheet  576 . In such a configuration, the igniter  638  and/or the flame sensor  640  extends horizontally through the tube sheet  576  and the tube sheet insulation  698 , and into the combustion region  788  of the combustion chamber enclosure  636  with the igniter  638  positioned adjacent the lower discharge mesh plate  766  of the burner  634 . This configuration allows for reliable positioning of the igniter  638  with respect to the burner  634 , and positions the igniter  638  perpendicular to the flow of gas, which exposes the igniter  638  to a greater surface area of gas and allows for more reliable ignition. 
     Returning to  FIGS.  67  and  68   , the second water header manifold  574  can be a single unitary structure or can include multiple components interconnected. The second water header manifold  574  can be formed from plastic due to economy of materials and corrosion resistance. For example, the water header manifold  574  can be similar in construction to the disclosure of U.S. Pat. No. 7,971,603, the contents of which are hereby incorporated by reference in their entirety. The second water header manifold  574  can include a main body  796  and a circulation body  798 . The second water header manifold  574  is shown in greater detail in  FIGS.  79 - 81   . 
       FIGS.  79  and  80    are first and second perspective views of the second water manifold header  574 .  FIG.  81    is an exploded perspective view of the second water manifold header  574 . The main body  796  of the second water manifold header  574  can include an first portion  800  having an inlet  802  and a second portion  804  having an outlet  806 . The inlet  802  and the outlet  806  can be threaded to assist with connection of an inlet fitting  888  and an outlet fitting  890 , respectively, as shown and described in connection with  FIG.  88   . The first and second portions  800 ,  804  can be detachably engaged to each other with a pressure valve  808  positioned therebetween, which can act as a bypass valve that opens when the pressure in the main body  796  is greater than a predetermined threshold (e.g., pounds per square inch) and closes when the pressure is below a predetermined threshold, which is discussed in greater detail below. The main body  796  also includes a first inlet port  810   a , a second inlet port  810   b , an eight outlet port  812   h , and a ninth outlet port  812   i  (the third, fourth, fifth, sixth, seventh, eighth, and ninth inlet ports  810   c ,  810   d ,  810   e ,  810   f ,  810   g ,  810   h ,  810   i , and the first, second, third, fourth, fifth, sixth, and seventh outlet ports  812   a ,  812   b ,  812   c ,  812   d ,  812   e ,  812   f ,  812   g  are discussed below) that are in fluidic communication with pipes  718  of the heat exchanger  696 , and discussed in greater detail below. A spacer  814  and an o-ring  816  can be placed in each of the inlet ports  810  and outlet ports  812  to create a proper watertight seal with the open end  722  of the pipe  718  engaged therewith. 
     The circulation body  798  includes a first arm  818 , a second arm  820 , a first cartridge  822 , and a second cartridge  824 . The first arm  818  defines a first inner cavity  826  and the second arm  820  defines a second inner cavity  828 , such that the first cartridge  822  can be removably inserted into the first inner cavity  826  through a first top opening  830  in the first arm  818  and the second cartridge  824  can be removably inserted into the second inner cavity  828  through a second top opening  832  in the second arm  820 . The first and second arms  818 ,  820  additionally include upper securing collars  834 ,  836  adjacent the first top opening  830  and the second top opening  832 , respectively. The upper securing collars  834 ,  836  each includes a through-hole  838  that assists in securing the first and second cartridges  822 ,  824  within the first and second arms  818 ,  820 . Specifically, when the first and second cartridges  822 ,  824  are removably placed within the first and second arms  818 ,  820 , locking mechanisms  840  (e.g., locking rods) can be inserted through the through-holes  838  of the upper securing collars  834 ,  836  and placed within a channel  842  that extends across a top of each of the first and second cartridges  822 ,  824 . The locking rods  840  can be secured in placed by a standard fastener or insert known in the art, e.g., a hairpin. This also aligns the cartridges  822 ,  824  within the first and second arms  818 ,  820 . This configuration allows for the first and second cartridges  822 ,  824  to be removed from the circulation body  798  to be serviced, cleaned, replaced, etc. For example, if it is determined that the circulation body  798  is clogged, e.g., there is poor circulation through the heat exchanger  696 , then a user can remove the cartridges  822 ,  824  and clean the circulation body  798  or the cartridges  822 ,  824  themselves. 
     The circulation body  798  additionally includes a plurality of inlet ports and outlet ports on a rear thereof. Specifically, the circulation body  798  includes the third inlet port  810   c , the fourth inlet port  810   d , the fifth inlet port  810   e , the sixth inlet port  810   f , the seventh inlet port  810   g , the eighth inlet port  810   h , the ninth inlet port  810   i , the first outlet port  812   a , the second outlet port  812   b , the third outlet port  812   c , the fourth outlet port  812   d , the fifth outlet port  812   e , the sixth outlet port  812   f , and the seventh outlet port  812   g . The fluid circuits between the inlet ports  810   a - 810   i  and the outlet ports  812   a - 812   i  is discussed in greater detail in connection with  FIGS.  82  and  83   . The inlet ports  810   a - 810   i  and the outlet ports  812   a - 812   i  are dimensioned and configured to match the dimensions and configuration of the tube openings  708  of the tube sheet  576 , such that the open ends  722  of the tubes  718  can extend through the tube openings  708  of the tube sheet  576  and into the respective inlet ports  810   a - 810   i  and outlet ports  812   a - 812   i . The water header manifold  574  can be mounted to the tube sheet  576  via a plurality of mounts  813  with the inlet ports  810   a - 810   i  and outlet ports  812   a - 812   i  aligned with the tube openings  708 , which places the water header manifold  574  in fluidic communication with the heat exchanger tubes  718  of the heat exchanger  696 . 
     The first and second cartridges  822 ,  824  are identical in construction such that they are interchangeable. The first and second cartridges  822 ,  824  include a body  844  that extends between a bottom plate  846  and a top cap  848 . The body  844  includes a plurality of openings  850  extending therethrough that are configured to align with the third inlet ports  810   c - 810   i  and the outlet ports  812   a - 812   g  of the circulation body  798  when the first and second cartridges  822 ,  824  are inserted into the first and second arms  818 ,  820  of the circulation body  798 , which allows for fluid to circulate into and out of the first and second inner cavities  826 ,  828  of the first and second arms  818 ,  820 . The plurality of openings  850  are sized, shaped, and positioned so that the first and second cartridges  822 ,  824  can be placed in either of the first or second arms  818 ,  820 . Additionally, the first and second cartridges  822 ,  824  each includes a horizontal divider  852  that is used to divide the first and second inner cavities  826 ,  828  of the first and second arms  818 ,  820  into chambers, as discussed in connection with  FIGS.  82  and  83   , and a vertical baffle  854  that is used to mix water paths in order to normalize the water temperature and prevent hot spots. 
       FIGS.  82  and  83    are perspective sectional and sectional views taken along Line  82 - 82  of  FIG.  65    generally showing the flow chambers within the second water header manifold  90 . The first portion  800  of the main body  796  forms an inflow chamber  856  and the second portion  804  forms an outflow chamber  858 , which are separated by the valve  808 . The inlet  802  (see  FIG.  79   ) is in fluidic communication with the inflow chamber  856  such that fluid supplied to the inlet  802  to be heated flows into the inflow chamber  856 , which is in fluidic communication with the first and second inlet ports  810   a ,  810   b . On the other hand, the outlet  806  (see  FIG.  79   ) is in fluidic communication with the outflow chamber  858  such that fluid that has been circulated through the heat exchanger  696 , and has been heated, flows into the outflow chamber  858  via the eighth and ninth outlet ports  812   h ,  812   i . The inflow chamber  856  and the outflow chamber  858  are capable of being switched into and out of fluidic communication by way of the pressure valve  808 , which opens when the pressure in the inflow chamber  856  is greater than a predetermined threshold (e.g., pounds per square inch) and closes when the pressure is below a predetermined threshold. When the pressure valve  808  is open, the inflow chamber  856  is in fluidic communication with the outflow chamber  858 , which allows a portion of the water to bypass the heat exchanger  696  resulting in a reduction in pressure in the system. Such functionality can be implemented in accordance with U.S. Pat. No. 7,971,603, the contents of which are hereby incorporated by reference in their entirety. 
     When the first and second cartridges  818 ,  820  are installed in the circulation body  798 , the circulation body  798  is divided into five chambers  860 ,  862 ,  864 ,  866 ,  868 . The first chamber  860  is defined between the top cap  848  of the first cartridge  818  and the horizontal divider  852  of the first cartridge  818 , and is in fluid communication with the first outlet  812   a  and the third inlet  810   c . The second chamber  862  is defined between the horizontal divider  852  of the first cartridge  818  and the bottom plate  846  of the first cartridge  818 , and is in fluid communication with the second outlet  812   b , third outlet  812   c , fourth inlet  810   d , and fifth inlet  810   e . The second chamber  862  can be divided into first and second sections  862   a ,  862   b  by the vertical baffle  854  with the third outlet  812   c  and the fourth inlet  810   d  positioned in the first section  862   a , and the fifth inlet  810   e  positioned in the second section  862   b . By dividing the second chamber  862  into the two sections  862   a ,  862   b  the water flowing through the different water paths can be mixed, which normalizes the temperature between the tubes  718 , e.g., prevents the outside tubes  718  from getting hotter than the inside tubes  718 . The third chamber  864  is defined between the bottom plate  846  of the first cartridge  818  and the bottom plate  846  of the second cartridge  820 , and is in fluid communication with the fourth outlet  812   d  and the sixth inlet  810   f . The fourth chamber  866  is defined between the horizontal divider  852  of the second cartridge  820  and the bottom plate  846  of the second cartridge  820 , and is in fluid communication with the fifth outlet  812   e , sixth outlet  812   f , seventh inlet  810   g , and eight inlet  810   h . The fourth chamber  866  can be divided into first and second sections  866   a ,  866   b  by the vertical baffle  854  with the fifth outlet  812   e  positioned in the first section  866   a , and the sixth outlet  812   f  and the seventh inlet  810   g  positioned in the second section  862   b . By dividing the fourth chamber  866  into the two sections  866   a ,  866   b  the water flowing through the different water paths can be mixed, which normalizes the temperature between the tubes  718 , e.g., prevents the outside tubes  718  from getting hotter than the inside tubes  718 . 
     It should be understood that the first inlet  810   a  is connected and in fluidic communication with the first outlet  812   a  by a tube  718 , the second inlet  810   b  is connected and in fluidic communication with the second outlet  812   b  by a tube  718 , the third inlet  810   c  is connected and in fluidic communication with the third outlet  812   c  by a tube  718 , the fourth inlet  810   d  is connected and in fluidic communication with the fourth outlet  812   d  by a tube  718 , the fifth inlet  810   e  is connected and in fluidic communication with the fifth outlet  812   e  by a tube  718 , the sixth inlet  810   f  is connected and in fluidic communication with the sixth outlet  812   f  by a tube  718 , the seventh inlet  810   g  is connected and in fluidic communication with the seventh outlet  812   g  by a tube  718 , the eighth inlet  810   h  is connected and in fluidic communication with the eighth outlet  812   h  by a tube  718 , and the ninth inlet  810   i  is connected and in fluidic communication with the ninth outlet  812   i  by a tube  718 . 
     Accordingly, water flows through the water header manifold  574  in the following fluid circuit: fluid enters the water header manifold  574  through the inlet  802  and into the inflow chamber  856 ; from the inflow chamber  856  the fluid flows into the first inlet  810   a  and the second inlet  810   a ; the fluid that enters into the first inlet  810   a  flows through a tube  718  and exits from the first outlet  812   a  into the first chamber  860  while the fluid that enters into the second inlet  810   b  flows through a tube  718  and exits from the second outlet  812   b  in the second chamber  862 ; the fluid that exits from the first outlet  812   a  into the first chamber  860  next enters the third inlet  810   c , flows through a tube  718 , and exits from the third outlet  812   c  in the first section  862   a  of the second chamber  862 ; the fluid that enters the second chamber  862  from the second outlet  812   b  and the third outlet  812   c  mix and enter the fourth inlet  810   d  (in the first section  862   a  of the second chamber  862 ) and the fifth inlet  810   e  (in the second section  862   b  of the second chamber  862 ); the fluid that enters into the fourth inlet  810   d  flows through a tube  718  and exits from the fourth outlet  812   d  into the third chamber  864  while the fluid that enters into the fifth inlet  810   e  flows through a tube  718  and exits from the fifth outlet  812   e  into the first section  866   a  of the fourth chamber  866 ; the fluid that exits from the fourth outlet  812   d  into the third chamber  864  next enters into the sixth inlet  810   f , flows through a tube  718 , and exits from the sixth outlet  812   f  in the second section  866   b  of the fourth chamber  866 ; the fluid that enters the fourth chamber  866  from the fifth outlet  812   e  and the sixth outlet  812   f  mix and enter the seventh inlet  810   g  and the eight inlet  810   h ; the fluid that enters into the seventh inlet  810   g  flows through a tube  718  and exits from the seventh outlet  812   g  in the fifth chamber  868  while the fluid that enters into the eight inlet  810   h  flows through a tube  718  and exits from the eight outlet  812   h  into the outflow chamber  858 ; the fluid that exits the seventh outlet  812   g  into the fifth chamber  868  next enters the ninth inlet  810   i , flows through a tube  718 , and exits from the ninth outlet  812   i  into the outflow chamber  858 ; and the fluid that enters the outflow chamber  858  through the eighth outlet  812   h  and the ninth outlet  812   i  exits the water header manifold  574  through the outlet  806 . As the water is circulated through the tubes  718  of the heat exchanger  696 , and between the inlets  810   a - i  and outlets  812   a - i , it is heated and recirculated to the pool or spa. 
     As referenced above,  FIGS.  84 - 88    show the alternative burner  774  in greater detail.  FIG.  84    is a partial perspective view illustrating the burner  774  connected with the combustion blower  572  and the combustion chamber enclosure  636 ,  FIG.  85    is a top plan view illustrating the burner  774  connected with the combustion blower  572  and the combustion chamber enclosure  636 , and  FIG.  86    is a partially exploded perspective view of the combustion blower  572 , combustion chamber enclosure  636 , and burner  774  of  FIGS.  84  and  85   .  FIG.  87    is a bottom perspective view of the burner  774 . As previously noted, the burner  774  shown and described in connection with  FIGS.  84 - 88    can be used in place of the burner  634  shown and described in connection with  FIGS.  67  and  68   , such that the burner  634  shown in  FIGS.  67 - 68    and the burner  774  shown in  FIGS.  84 - 87    are interchangeable based on a user&#39;s desired configuration. 
     The burner  774  includes a body  870 , a top mounting plate  872 , a gasket  874 , and a perforated bottom plate  876 . The top mounting plate  872  includes a central opening  878  and perimeter holes  880  that the igniter  638  and flame sensor  640  can extend through. The body  870  can be a rectangular-shaped box and can include an upper mounting flange  882  that assists with mounting the burner  774  to the top  776   e  of the combustion chamber enclosure  636 . A plurality of holes  884  can be provided in the upper mounting flange  882  that the igniter  638  and flame sensor  640  can extend through. 
     The burner  774  can be mounted to the top  776   e  of the combustion chamber enclosure  636  with the body  870  extending through the burner opening  780  into the combustion chamber cavity  784  of the combustion chamber enclosure  636 . Furthermore, when the burner  774  is mounted to the top  776   e  of the combustion chamber enclosure  636 , the body  870  can be positioned within the top gap  760  of the heat exchanger  696  mounted within the combustion chamber enclosure  36 . This can be seen, for example, in  FIG.  88   , which is a sectional view taken along Line  88 - 88  of  FIG.  85   . The combustion blower  572  can be mounted to the mounting plate  872  of the burner  774  with the outlet  656  of the combustion blower  572  positioned over the central opening  878 . This configuration allows for the air/gas mixture discharged from the outlet  656  of the combustion blower  572  to flow through the central opening  878  and into an internal cavity  886  defined by the body  870  of the burner  774 . The air/gas mixture to be ignited by the igniter  638  is then dissipated from the internal cavity  886  and through the lower perforated bottom plate  876  into the combustion chamber canister  636 . The burner  774  can also include a distributor plate (not shown) positioned within the internal cavity  886  adjacent the central opening  878 , which functions to evenly distribute the air/gas mixture provided by the combustion blower  572  to the burner  774 , allowing for a normalized ignition of the air/gas mixture. The igniter  638  and the flame sensor  640  can be inserted through the perimeter holes  880  of the top mounting plate  872  and the holes  884  in the upper mounting flange  882  of the burner body  870 , and mounted to the top mounting plate  827 . 
     When inserted through the holes  880 ,  884 , the igniter  638  and the flame sensor  640  extend vertically into the first and second cutouts  792 ,  794  of the front heat exchanger insulation  700  and into the combustion region  788  of the combustion chamber enclosure  636 . When the igniter  638  and the flame sensor  640  are mounted to the top mounting plate  872 , and the burner  774  is mounted to the combustion chamber enclosure  636  within the burner opening  780 , the igniter  638  and the flame sensor  640  will be at a pre-set desired distance from the perforated bottom plate  876  from which the air/gas mixture is dissipated. As previously discussed, this distance is the desired distance to achieve efficient and safe ignition of the air/gas mixture dissipated from the burner  774 . Consistency of this spacing is achieved by mounting the igniter  638  (and the flame sensor  640 ) to the burner  774 , and mounting both the igniter  638  and the burner  774  to the top  776   e  of the combustion chamber enclosure  636 , which drastically reduces the number of components that contribute to the “stack-up” of tolerances. In essence, this reduces the tolerance stack to the holes  880 ,  884  through which the igniter  638  extends. 
       FIG.  89    is a perspective view showing a third inlet fitting  888  and a third outlet fitting  890  of the present disclosure. The third inlet fitting  888  and the third outlet fitting  890  shown in  FIG.  88    are similar in construction and functionality to the second inlet fitting  390  and the second outlet fitting  392  shown and described in connection with  FIGS.  37  and  38   . Accordingly, it should be understood that the third inlet fitting  888  can be utilized to adapt the water manifold header  574  inlet  802  to the inlet position of a prior heater that is being replaced, and the third outlet fitting  890  can be utilized to adapt the water manifold header  574  outlet  806  to the outlet position of the prior heater that is being replaced, in the same fashion as the second inlet fitting  390  and the second outlet fitting  392 . 
     The third inlet fitting  888  includes a third inlet fitting inlet  892 , a third inlet fitting body  894 , a third inlet fitting outlet  896 , and a third inlet fitting fastener  898 . The third inlet fitting  888  forms a fluidic path between the third inlet fitting inlet  892 , the third inlet fitting body  894 , and the third inlet fitting outlet  896 , such that fluid can flow into the third inlet fitting inlet  892 , across the third inlet fitting body  888 , and out of the third inlet fitting outlet  896 . Additionally, the third inlet fitting inlet  892  can be threaded to allow for connection with a corresponding threaded fastener associated with pre-existing plumbing in order to connect the water manifold header  574  to the pre-existing plumbing. The third inlet fitting fastener  898  can be a threaded nut that can be captured/retained on the third inlet fitting  888  adjacent the third inlet fitting outlet  896 . The third inlet fitting fastener  898  is configured to threadedly engage the threaded inlet  802  of the water manifold header  574  in order to secure the third inlet fitting  888  to the water manifold header  574 . The third inlet fitting fastener  898  allows for increased positional freedom of the third inlet fitting inlet  892 . Specifically, the third inlet fitting  888  can be secured to the threaded inlet  802  of the water header manifold  574  by aligning the third inlet fitting fastener  898  with the threaded inlet  802 , partially tightening the third inlet fitting fastener  898  on the threaded inlet  802 , rotating the third inlet fitting  888  to adjust the horizontal and vertical placement of the third inlet fitting inlet  892  to the desired position (e.g., to the second inlet fitting height IFH 2  as shown in  FIG.  38   ), and then fully tightening the third inlet fitting fastener  898  once the third inlet fitting inlet  892  is in the desired position to fix the third inlet fitting inlet  892  in that position, which places the threaded inlet  802  in fluidic communication with the third inlet fitting inlet  892 . This capability allows for a user to account for variations that may be present in the position of pre-existing water outlet plumbing (e.g., that was connected to the prior heater that gas heater  10 ,  510  is replacing) with which the user wishes to align the third inlet fitting inlet  892 . When the third inlet fitting  888  is connected to the water header manifold  574 , the third inlet fitting inlet  892  will be at an adjusted inlet position that is associated with the inlet of a second heater, e.g., a water manifold of a second heater, that is different than the new heater being installed  10 ,  510 . That is, the third inlet fitting inlet  892  will be at substantially the same position as the inlet of the previously installed second heater that is being replaced so that the third inlet fitting inlet  892  can be easily connected to pre-existing plumbing to which the second heater was connected, e.g., piping that extends from a pump. 
     The third outlet fitting  890  includes a third outlet fitting outlet  900 , a third outlet fitting body  902 , a third outlet fitting inlet  904 , and a third outlet fitting fastener  906 . The third outlet fitting  890  forms a fluidic path between the third outlet fitting inlet  904 , the third outlet fitting body  902 , and the third outlet fitting outlet  900 , such that fluid can flow into the third outlet fitting inlet  904 , across the third outlet fitting body  902 , and out of the third outlet fitting outlet  900 . Additionally, the third outlet fitting outlet  900  can be threaded to allow for connection with a corresponding threaded fastener associated with pre-existing plumbing in order to connect the water manifold header  574  to the pre-existing plumbing. The third outlet fitting fastener  906  can be a threaded nut that can be captured/retained on the third outlet fitting  890  adjacent the third outlet fitting inlet  904 . The third outlet fitting fastener  906  is configured to threadedly engage the threaded outlet  806  of the water manifold header  574  in order to secure the third outlet fitting  890  to the water manifold header  574 . The third outlet fitting fastener  906  allows for increased positional freedom of the third outlet fitting outlet  900 . Specifically, the third outlet fitting  890  can be secured to the threaded outlet  806  of the water header manifold  574  by aligning the third outlet fitting fastener  906  with the threaded outlet  806 , partially tightening the third outlet fitting fastener  906  on the threaded outlet  806 , rotating the third outlet fitting  890  to adjust the horizontal and vertical placement of the third outlet fitting outlet  900  to the desired position (e.g., to the second outlet fitting height OFH 2  as shown in  FIG.  38   ), and then fully tightening the third outlet fitting fastener  906  once the third outlet fitting outlet  900  is in the desired position to fix the third outlet fitting outlet  900  in that position, which places the threaded outlet  806  in fluidic communication with the third outlet fitting outlet  900 . This capability allows for a user to account for variations that may be present in the position of pre-existing water inlet plumbing (e.g., that was connected to the prior heater that gas heater  10 ,  510  is replacing) with which the user wishes to align the third outlet fitting outlet  900 . When the third outlet fitting  890  is connected to the water header manifold  574 , the third outlet fitting outlet  900  will be at an adjusted outlet position that is associated with the outlet of the second heater, e.g., the water manifold of the second heater, that is different than the new heater being installed  10 ,  510 . That is, the third outlet fitting outlet  900  will be at substantially the same position as the outlet of the previously installed second heater that is being replaced so that the third outlet fitting outlet  900  can be easily connected to pre-existing plumbing to which the second heater was connected, e.g., piping that extends to a pool water circulation system. 
     Accordingly, the third inlet fitting  888  can be secured to the water header manifold  574  to adjust the inlet height H I  to the second inlet fitting height IFH 2  in the same fashion as the second inlet fitting  390 , and the third outlet fitting  890  can be secured to the water header manifold  574  to adjust the outlet height H O  to the second outlet fitting height OFH 2  in the same fashion as the second outlet fitting  392 . It should also be understood that while reference is made herein to the second inlet fitting  390 , the third inlet fitting  888 , the second outlet fitting  392 , and the third outlet fitting  890  adjusting inlet height and the outlet height to a new effective height, such functionality is capable of adjusting the overall effective position of the water header manifold inlet  346 ,  802  and water header manifold outlet  350 ,  806 , including the horizontal/lateral position and depth thereof in addition to the vertical position. Such is shown, for example, in  FIG.  37    where the effective horizontal/lateral position of the inlet  346  and the outlet  350  is adjusted horizontally/laterally towards the center of the gas heater  10  by the second inlet fitting  390  and the second outlet fitting  392 , and in  FIG.  35    where the effective depth of the inlet  346  and the outlet  350  is adjusted outward away from the gas heater  10  by the first inlet fitting  378  and the first outlet fitting  380 . 
     While exemplary embodiments have been described herein, it is expressly noted that these embodiments should not be construed as limiting, but rather that additions and modifications to what is expressly described herein also are included within the scope of the disclosure. Moreover, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations are not made express herein.