Patent Publication Number: US-2023147831-A1

Title: Gas furnace and air conditioner having the same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2021-0151811, filed Nov. 5, 2021, whose entire disclosures are hereby incorporated by reference. 
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to a gas furnace and an air conditioner having the same. 
     Related Art 
     In general, an air conditioner refers to an apparatus for cools and heating an indoor space through compression, condensation, expansion, and evaporation of refrigerant. The air conditioner can improve indoor air quality by exchanging indoor unit with outdoor air through a ventilator. In addition, the ventilator may increase the temperature of air supplied to the indoor space by using high-temperature combustion gas of a gas furnace. 
     U.S. Pat. No. 5,186,620 (registered on Feb. 16, 1993) and U.S. Pat. No. 6,860,734 B2 (registered on Mar. 1, 2005) disclose an in shot burner having a venturi tube and a retainer. In this case, primary air is introduced into a burner by fuel, which is injected from a nozzle to the burner, and mixed with the fuel. Then, the mixture of the fuel and the primary air is combusted together with secondary air sucked into an exit of the burner by an inducer. However, in terms of flame stability, there is a problem in that it is difficult to increase a Top Down Ratio (TDR), which is a ratio of maximum thermal power to minimum thermal power of the gas furnace. 
     International Patent Application. WO 2005-095870 A1 (published on Oct. 13, 2005) discloses a gas furnace in which a plurality of burners are classified into two groups and thermal power of each group is independently controlled. 
     Specifically, a manifold of the gas furnace is divided into two sections by a separator plate, and each of the two sections communicates with each of the two groups. In addition, the gas furnace has a first gas valve for supplying fuel to one of the two sections, and a second gas valve for supplying fuel to the other of the two sections. That is, the above gas furnace controls the thermal power of the respective groups individually by using the first gas valve and the second gas valve, and adjusts the thermal power of the gas furnace stepwise. 
     In this case, in order to reduce the thermal power of the gas furnace, the opening degree of the respective gas valves may be reduced, or any one of the gas valves may be closed with the other one being opened so as to supply fuel to some of the burners. 
     However, this control is a control to reduce the amount of fuel supplied to each burner or the number of burners to which fuel is supplied, while the minimum thermal power of each burner is fixed, so there is a limitation in reducing the thermal power of the gas furnace. Here, the burner of the gas furnace is an in-shot burner in which primary air introduced into an entry of a burner and secondary air introduced into an exit of the burner participate in a combustion process, as similarly as in the above-mentioned US patents, and the burner is designed to have a specific minimum thermal power. 
     SUMMARY OF THE DISCLOSURE 
     An aspect of the present disclosure is to solve the above-described problems and other problems. 
     Another aspect of the present disclosure provides a gas furnace capable of providing a user with thermal comfort and reducing heating cost and energy by implementing a high Top Down Ratio (TDR). 
     Yet another aspect of the present disclosure provides a gas furnace capable of changing a shape of a flame according to a required thermal power. 
     Yet another aspect of the present disclosure provides a mechanism capable of allowing or blocking introduction of primary air to a burner. 
     Yet another aspect of the present disclosure provides various methods for controlling the above mechanism according to the required firepower. 
     According to an aspect of the present disclosure, there is provided a gas furnace including: a burner for burning fuel; a manifold providing the fuel to an entry of the burner; a heat exchanger spaced apart from an exit of the burner and providing a passage for combustion gas generated by the burner; an inducer for causing a fluid to flow through the burner and the heat exchanger; a blower for causing a flow of air passing around the heat exchanger; and an air shutter positioned between the manifold and the entry of the burner. 
     According to another aspect of the present disclosure, the air shutter may include: a housing having an inner space that communicates with the manifold and the entry of the burner; and a primary hole formed to penetrate the housing and able to be opened and closed. 
     According to another aspect of the present disclosure, the gas furnace may further include: a nozzle having one side coupled to the manifold and the other side coupled to the housing. 
     According to another aspect of the present disclosure, the nozzle may face the entry of the burner, and the primary hole may be positioned between the nozzle and the entry of the burner. 
     According to another aspect of the present disclosure, the burner may include a plurality of burners spaced apart from each other, and the housing may extend in a direction in which the plurality of burners is spaced apart from each other. 
     According to another aspect of the present disclosure, the primary hole may include: a plurality of primary holes spaced apart from each other in a longitudinal direction of the housing. 
     According to another aspect of the present disclosure, the plurality of primary holes may be simultaneously opened or closed. 
     According to another aspect of the present disclosure, the plurality of primary holes may further include a plurality of lower holes formed to penetrate one side of the housing and provided in a number equal to a number of the plurality of burners. 
     According to another aspect of the present disclosure, the air shutter may include: a first rack coupled to the one side of the housing to be movable in the longitudinal direction of the housing, the first rack having a plurality of first holes that is formed to penetrate the first rack and spaced apart from each other at intervals identical to intervals between the plurality of lower holes. 
     According to another aspect of the present disclosure, the plurality of primary holes may further include a plurality of upper holes formed to penetrate the other side of the housing and facing the plurality of lower holes. 
     According to another aspect of the present disclosure, the air shutter includes: a second rack coupled to the other side of the housing to be movable in the longitudinal direction of the housing, the second rack having a plurality of second holes that are formed to penetrate the second rack and spaced apart from each other at intervals identical to intervals between the plurality of upper holes. 
     According to another aspect of the present disclosure, the first rack and the second rack may be movably coupled to an inside of the housing. 
     According to another aspect of the present disclosure, the air shutter may include: a rotary motor located outside the housing and having a rotational shaft penetrating the housing; and a pinion fixed to the rotational shaft of the rotary motor and engaged with the first rack and the second rack at a position between the first rack and the second rack. The pinion may be rotatable in a first rotational direction or in a second rotational direction opposite to the first rotational direction. 
     According to another aspect of the present disclosure, a length of the first rack may be greater than a length of the second rack, and a number of the plurality of first holes may be greater than a number of the plurality of second holes. 
     According to another aspect of the present disclosure, the pinion may be rotatable stepwise. 
     According to another aspect of the present disclosure, the gas furnace includes: a fuel valve providing the fuel to the manifold; and a controller configured to control the rotary motor, the fuel valve, and the inducer. 
     According to another aspect of the present disclosure, the controller may be further configured to, in response to a required load being greater than a first load but less than a maximum load, control the rotary motor so as to fully open the plurality of lower holes and the plurality of upper holes. In addition, the controller may be further configured to control an opening degree of the fuel valve and a revolution per minute (RPM) of the inducer to correspond to the required load. 
     According to another aspect of the present disclosure, the controller may be further configured to: in response to the required load being less than or equal to the first load, control the rotary motor so as to fully close at the plurality of lower holes and the plurality of upper holes. In addition, the controller may be further configured to control an opening degree of the fuel valve and a revolution per minute (RPM) of the inducer to correspond to the required load. 
     According to another aspect of the present disclosure, the controller may be further configured to: in response to the required load being greater than the second load but less than the first load, control the rotary motor so as to partially open the plurality of lower holes and the plurality of upper holes. In addition, the controller may be further configured to control an opening degree of the fuel valve and a revolution per minute (RPM) of the inducer to correspond to the required load. 
     According to another aspect of the present disclosure, the controller may be further configured to: in response to the required load being less than or equal to the second load, control the rotary motor so as to fully close at the plurality of lower holes and the plurality of upper holes. In addition, the controller may be further configured to control an opening degree of the fuel valve and a revolution per minute (RPM) of the inducer to correspond to the required load. 
     According to another aspect of the present disclosure, the housing may include: a first housing opened upward; and a second housing opened downward and detachably coupled to the first housing. 
     According to another aspect of the present disclosure, the gas furnace may further include: a first shell extending along the first housing and coupled to one side of the first housing, the first shell having a plurality of lower parts that are formed by being pressed from an upper surface of the first sell and are spaced apart from each other in a longitudinal direction of the first shell. 
     In addition, the gas furnace may further include: a second shell extending along the second housing and coupled to one side of the second housing, the second shell having a plurality of upper parts that are formed by being pressed upward from a lower surface of the second shell and spaced apart from each other in a longitudinal direction of the second shell and face the plurality of lower parts. 
     In addition, the plurality of burners may include: the plurality of lower parts; and the plurality of upper parts. 
     According to another aspect of the present disclosure, the first shell may further include: a first flange that is a portion of the first shell other than the plurality of lower parts. 
     The second shell may further include: a second flange that is a portion of the second shell other than the plurality of upper parts and detachably coupled to the first flange. 
     In addition, the flame propagation port may be formed in a portion between the first flange and the second flange positioned between the plurality of burners. 
     According to another aspect of the present disclosure, the gas furnace may further include: an igniter adjacent to an exit of a burner positioned at one end of the plurality of burners. 
     According to another aspect of the present disclosure, the gas furnace may further include: a flame detector adjacent to an exit of a burner positioned at the other end of the plurality of burners. 
     According to another aspect of the present disclosure, each of the plurality of burners may further include: a venturi portion forming an entry of each of the plurality of burners; a head portion forming an exit of each of the plurality of burners; and a retainer inserted into the head portion. 
     According to another aspect of the present disclosure, there is provided an air conditioner having an outdoor unit and a ventilator connected to each other through a refrigerant pipe. The ventilator may include: an air supply fan for causing a flow of air along an air supply passage; an exhaust fan for causing a flow of air along an exhaust passage separated from the air supply passage; a plurality of coils located in the air supply passage and having refrigerant flowing therethrough; and a gas furnace positioned downstream of the plurality of coils in the air supply passage. 
     A gas furnace and an air conditioner having the same according to the present disclosure may have effects as below. 
     According to at least one of the embodiments of the present disclosure, it is possible to adjust the intensity of thermal power stepwise by adjusting an opening degree of a fuel valve. 
     According to at least one of the embodiments of the present disclosure, by using an air shutter to convert the characteristics of a flame from a partially premixed flame in which primary air and secondary air participate in combustion to a diffuse flame in which only secondary air participates in combustion, it is possible to realize a high Top Down Ratio (TDR). That is, it is possible to provide a gas furnace capable of providing thermal comfort to a user and reducing cost and energy. 
     According to at least one of the embodiments of the present disclosure, it is possible to control opening and closing of a primary hole of an air shutter. That is, a gas furnace capable of changing a shape of a flame according to a required thermal power may be provided. 
     According to at least one of the embodiments of the present disclosure, it is possible to open or close a primary hole of an air shutter by use of movement of a rack in the air shutter. That is, a mechanism for allowing or blocking the introduction of primary air to a burner through a primary hole of an air shutter may be provided. 
     According to at least one of the embodiments of the present disclosure, it is possible to control a movement direction of a rack connected to a rotary motor by using the rotary motor. That is, various methods for controlling the above mechanism may be provided according to a required thermal power. 
     According to at least one of the embodiments of the present disclosure, an opening degree of a primary hole of an air shutter may be adjusted. That is, a shape of a flame may be changed stepwise according to a required thermal power. 
     According to at least one of the embodiments of the present disclosure, a plurality of shell-type burners formed integrally with the air shutter as one body may be provided. 
     According to at least one of the embodiments of the present disclosure, a flame propagation port may be formed between the plurality of burners. That is, the number of igniters and flame detectors provided in the plurality of burners may be minimized. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1  and  2    are views showing an internal configuration of an air conditioner according to an embodiment of the present disclosure. 
         FIGS.  3  and  4    are views showing a gas furnace according to an embodiment of the present disclosure. 
         FIG.  5    is an exploded perspective view of an air shutter according to an embodiment of the present disclosure. 
         FIG.  6    is an enlarged view of a portion of an air shutter and a burner according to an embodiment of the present disclosure. 
         FIG.  7    is a perspective view of a shutter assembly of an air shutter according to an embodiment of the present disclosure. 
         FIG.  8    is a control configuration diagram of a gas furnace according to an embodiment of the present disclosure. 
         FIG.  9    is a flowchart illustrating a method for controlling a gas furnace according to an example of the present disclosure. 
         FIGS.  10  and  11    are views showing a state in which a primary hole of an air shutter is opened according to an embodiment of the present disclosure. 
         FIGS.  12  and  13    are views showing a state in which a primary hole of an air shutter is closed according to an embodiment of the present disclosure. 
         FIG.  14    is a flowchart of a method for controlling a gas furnace according to another example of the present disclosure. 
         FIG.  15    is a view illustrating a state in which a primary hole of an air shutter is partially opened according to an embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings, but the same or similar components are assigned the same reference numerals regardless of reference numerals, and redundant description thereof will be omitted. 
     The suffixes “module” and “part” for components used in the following description are given or mixed in consideration of only the ease of writing the specification, and do not have distinct meanings or roles by themselves. 
     In addition, in describing the embodiments disclosed in the present specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. In addition, the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and the technical spirit disclosed in the present specification is not limited by the accompanying drawings, and all changes included in the spirit and scope of the present disclosure, should be understood to include equivalents or substitutes. 
     Terms including ordinal numbers such as first, second, etc. may be used to describe various elements, but the elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. 
     When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. On the other hand, when it is said that a certain component is “directly connected” or “directly connected” to another component, it should be understood that the other component does not exist in the middle. 
     A singular expression includes a plural expression unless the context clearly dictates otherwise. 
     In the following description, even if an embodiment is described with reference to specific figure, a reference numeral not indicated in the specific figure may be referred to if necessary, and the reference numeral not indicated in the specific figure may be used when indicated in the other figure. 
     The directions of upward (U, y), downward (D), leftward (Le, x), rightward (Ri), forward (F, z), and rear direction (R) indicated in  FIG.  2    are used for convenience of explanation, and the technical spirit of the present disclosure is not limited thereby. 
     Referring to  FIGS.  1  and  2   , an air conditioner  1  may include an outdoor unit  20  and a ventilator  10 . The outdoor unit  20  may include a compressor (not shown) for compressing refrigerant and an outdoor heat exchanger (not shown) for performing heat exchange between refrigerant and outdoor air. The outdoor unit  20  may be connected to the ventilator  10  through a refrigerant pipe  11   a . The refrigerant may circulate the outdoor unit  20  and the ventilator  10  through the refrigerant pipe. A housing  10 H of the ventilator  10  may form the exterior of the ventilator  10 . 
     The housing  10 H may include a first long side LS1 and a second long side LS2 opposite to the first long side LS1. The first long side LS1 and the second long side LS2 may be collectively referred to as a long side LS1 and LS2. The housing  10 H may include a first short side SS1 adjacent to the long side LS1 and LS2 and a second short side SS2 opposite the first short side SS1. The first short side SS1 and the second short side SS2 may be collectively referred to as a short side SS1 and SS2. 
     A direction vertically to the long side LS1 and LS2 and the short side SS1 and SS2 may be referred to as a first direction DR1 or a left-right direction. A direction parallel to the short side SS1 and SS2 may be referred to as a second direction DR2 or an up-down direction. A direction parallel to the long side LS1 and LS2 may be referred to as a third direction DR3 or a front-rear direction. 
     A side of the first long side LS1 may be referred to as an upper side (U, y), and a side of the second long side LS2 may be referred to as a lower side (D). A side of the first short side SS1 may be referred to as a front side (F, z), and a side of the second short side SS2 may be referred to as a rear side (R). In the first direction DR1, a direction toward one end of the short side SS1 and SS2 may be referred to as a left side (Le, x), and a direction toward the other end of the short side SS1 and SS2 may be referred to as a right side (Ri). 
     The ventilator  10  may include a refrigerant distributor  11 , a plurality of heat exchangers  12 ,  13 ,  14 ,  15 , and  19 , a blower  16 , a partition  17 , and an exhaust fan  18 . The refrigerant distributor  11 , the plurality of heat exchangers  12 ,  13 ,  14 ,  15 , and  19 , the blower  16 , the partition  17 , and the exhaust fan  18  may be installed inside the housing  10 H. 
     An air supply passage OA-SA may be formed between a first inlet  10   i  and a first outlet (not shown). The first inlet  10   i  may be formed to penetrate the second short side SS2 and may be adjacent to the first long side LS1. The first outlet may be formed to penetrate the second long side LS2 and may be adjacent to the first short side SS1. Outdoor air OA may be introduced into the first inlet  10   i , and the first inlet  10   i  may be referred to as an outdoor air inlet. Supply air SA may be supplied into a room through the first outlet, and the first outlet may be referred to as a supply air outlet. 
     The blower  16  may be adjacent to the first outlet and located in the air supply passage OA-SA. The blower  16  may cause a flow of air along the air supply passage OA-SA. The blower  16  may be referred to as an air supply fan or a plug fan. Meanwhile, an air supply duct (not shown) may be connected to the second long side LS2 and may communicate with the first outlet and the indoor space. For example, the air volume per minute of the blower  16  may be 3,000 to 5,000 cubic feet per minute (CFM). 
     The exhaust passage RA-EA may be formed between the second inlet  10   p  and the second outlet  10   g . The second inlet  10   p  may be formed to penetrate the second long side LS2 and may be spaced apart from the first outlet. The second outlet  10   g  may be formed through the second short side SS2 and may be adjacent to the second long side LS2. The indoor air RA (room air, or return air) may be introduced into the second inlet  10   p , and the second inlet  10   p  may be referred to as an indoor air inlet. Exhaust air EA may be discharged to the outside through the second outlet  10   g , and the second outlet  10   g  may be referred to as an exhaust outlet. 
     The exhaust fan  18  may be located in the exhaust passage RA-EA adjacent to the second discharge port  10   g . The exhaust fan  18  may cause a flow of air along the exhaust passage RA-EA. The exhaust fan  18  may be referred to as a blower or a plug fan. On the other hand, the inner duct (not shown) may be connected to the second long side LS2, it may be in communication with the second inlet  10   p  and the indoor space. 
     The partition wall  17  may divide the inner space of the housing  10 H into a space in which the air supply passage OA-SA is formed and a space in which the exhaust passage RA-SA is formed. The partition wall  17  may be installed near the second inlet  10   p  of the housing  10 H, and may include an inclined portion (unsigned) and a horizontal portion (unsigned). Accordingly, the air supply passage OA-SA may be located above the partition wall  17 , and the exhaust passage RA-SA may be located below the partition wall  17 . 
     The refrigerant distributor  11  may be adjacent to the first long side LS1 and the first short side SS1. One side of the refrigerant distributor  11  may be connected to the refrigerant pipe ( 11   a ). The other side of the refrigerant distributor  11  may be connected to a plurality of pipes  11   b ,  11   c ,  11   d , and  11   e . For example, the refrigerant distributor  11  may open and close the passage of each pipe through a solenoid valve. Here, each pipe  11   b ,  11   c ,  11   d , or  11   e  may include a refrigerant pipe providing a passage of refrigerant supplied to each heat exchanger  12 ,  14 ,  15 , or  19 , and a refrigerant pipe providing a passage of refrigerant passing through each heat exchanger  12 ,  14 ,  15 , or  19 . In addition, each expansion valve (not shown) may expand the refrigerant flowing through each of the pipes  11   b ,  11   c ,  11   d , and  11   e . For example, the expansion valve may be an Electronic Expansion Valve (EEV) capable of adjusting the opening degree. In this case, when the expansion valve is fully opened, the expansion valve may not expand the refrigerant. 
     The preheater  12  may be located in the air supply passage OA-SA adjacent to the first inlet  10   i . A preheater  12  may be disposed vertically within the housing  10 H. A first pipe  11   b  may provide a refrigerant passage connecting the refrigerant distributor  11  and the preheater  12 . Accordingly, the preheater  12  may heat air introduced into the first inlet  10   i . The preheater  12  may be referred to as a preheat coil. 
     The heat exchanger  14  may be located downstream of the preheater  12  in the air supply passage OA-SA. The heat exchanger  14  may be vertically disposed within the housing  10 H. A size of the heat exchanger  14  may be larger than a size of the preheater  12 . The second pipe  11   c  may provide a refrigerant passage connecting the refrigerant distributor  11  and the heat exchanger  14 . The heat exchanger  14  may be referred to as a main heat exchanger or a cooling/heating coil. 
     A reheater  15  may be located downstream of the heat exchanger  14  in the air supply passage OA-SA. The reheater  15  may be vertically disposed within the housing  10 H. A size of the reheater  15  may be smaller than a size of the heat exchanger  14 . The third pipe  11   d  may provide a refrigerant passage connecting the refrigerant distributor  11  and the reheater  15 . The reheater  15  may be referred to as a reheat coil. Meanwhile, the reheater  15  may be operated based on a set indoor temperature and a set humidity. The reheater  15  may face the blower  16  with respect to a base  10 W on which the reheater  15  is installed. 
     A recovery coil  19  may be located in an exhaust passage RA-EA adjacent to the exhaust fan  18 . The recovery coil  19  may be vertically disposed within the housing  10 H. A fourth pipe  11   e  may provide a refrigerant passage connecting the refrigerant distributor  11  and the recovery coil  19 . Meanwhile, a heat transfer direction of the recovery coil  19  to air may be opposite to a heat transfer direction of the heat exchanger  14  to air. 
     A part of the recovery wheel  13  may be located in the air supply passage OA-SA between the preheater  12  and the heat exchanger  14 , and the other part of the recovery wheel  13  may be located in the exhaust passage RA-EA between the recovery coil  19  and the inclined portion of the partition wall  17 . The recovery wheel  13  may be referred to as an energy recovery wheel (ERW). 
     In this case, the recovery wheel  13  may have a flat cylinder shape as a whole. A honeycomb structure may be formed inside the recovery wheel  13 , and air may pass through the honeycomb structure. The recovery wheel  13  may be rotated at a low speed. Accordingly, the recovery wheel  13  may recover sensible heat and latent heat by using temperature difference and humidity difference between the outdoor air OA and the indoor air RA. 
     Referring to  FIGS.  2  and  3   , the blower  16  may include a motor  16   a , a hub  16   b , a shroud  16   c , and a plurality of blades  16   d . The hub  16   b , the shroud  16   c , and the plurality of blades  16   d  may be collectively referred to as an impeller  16   a ,  16   b , and  16   c.    
     The motor  16   a  may provide a rotational force. The motor  16   a  may be a centrifugal fan motor. The motor  16   a  may form a front end of the blower  16 , and a rotational shaft of the motor  16   a  may extend rearward from the motor  16   a . A longitudinal direction of the rotational shaft of the motor  16   a  may be referred to as an axial direction of the blower  16 . 
     The hub  16   b  may be located at the rear of the motor  16   a  and may be fixed to the rotational shaft of the motor  16   a . The hub  16   b  may have a disk shape. 
     The shroud  16   c  may be located at the rear of the hub  16   b  and may have a ring plate shape. The shroud  16   c  may be rotatably coupled to the base  10 W. For example, an inlet (unsigned) may be fixed to a front surface of the base  10 W between the shroud  16   c  and the base  10 W, and may have a hyperbolic cylinder or funnel shape. In this case, the shroud  16   c  may be rotatably coupled to the inlet. A hole formed inside the shroud  16   c , an inner space of the inlet, and a hole (not shown) formed in the base  10 W may communicate with one another and be located in the air supply passage OA-SA (see  FIG.  1   ). 
     The plurality of blades  16   d  may be located between an inner periphery and an outer periphery of the ring-shaped shroud  16   c . The plurality of blades  16   d  may be coupled to the hub  16   b  and the shroud  16   c  between the hub  16   b  and the shroud  16   c . The plurality of blades  16   d  may be formed integrally with the shroud  16   c  and the hub  16   b.    
     In addition, the plurality of blades  16   d  may be spaced apart from each other in a rotating direction of the rotational shaft of the motor  16   a . Each of the plurality of blades  16   d  may be convexly curved in the rotating direction of the rotational shaft (see  FIGS.  4  and  5   ). Among the plurality of blades  16   d , a blade positioned close to a mount plate  110  to be described later may be convex toward the mount plate  110 . 
     Accordingly, when the impeller  16   a ,  16   b , and  16   c  is rotated in a clockwise direction in response to driving of the motor  16   a , air may be introduced in an axial direction of the blower  16  through a hole of the base  10 W and may be pressed by the plurality of blades  16   d  to be discharged in a radial direction of the blower  16 . In this case, a flow of air discharged by the blower  16  may be concentrated on the left side of the blower  16  rather than the right side of the blower  16 . 
     A horizontal plate  10   a  may be vertically disposed on a front surface of the base  10 W, and may be coupled to the front surface of the base  10 W. The horizontal plate  10   a  may be located above the blower  16 . The horizontal plate  10   a  may be referred to as a first horizontal wall or a first panel. Meanwhile, a frame  16   e  may form a skeleton of the blower  16 , and a motor mount  1600  on which the motor  16   a  is mounted may be coupled to the frame  16   a . The frame  16   e  may be coupled to the bottom of the horizontal plate  10   a.    
     A top plate  10   b  may be disposed vertically to the front surface of the base  10 W, and may be coupled to the front surface of the base  10 W. The top plate  10   b  may be located below of the blower  16 . The top plate  10   b  may be referred to as a second horizontal wall or a second panel. A top hole  100   a  may be formed to penetrate the top plate  10   b  in the up-down direction. The top hole  100   a  may be formed to be long in the left-right direction. In the up-down direction, at least a portion of the top hole  100   a  may overlap the blower  16 . 
     A bottom plate  10   c  may be disposed vertically to the front surface of the base W, and may be coupled to the front surface of the base  10 W. The bottom plate  10   c  may face the horizontal plate  10   a  with respect to the top plate  10   b . The bottom plate  10   c  may form a part of the second long side LS2 of the housing  10 H. The bottom hole  100   b  may be formed to penetrate the bottom plate  10   c  in the up-down direction. The bottom hole  100   b  may be formed to be long in the left-right direction. In the up-down direction, the bottom hole  100   b  may face the top hole  100   a.    
     The side plate  10   d  may be disposed vertically to the front surface of the base W, and may be coupled to the front surface of the base W. The side plate  10   d  may be coupled to a right side of the horizontal plate  10   a , a right side of the top plate  10   b , and a right side of the bottom plate  10   c . A side hole  100   c  may be formed to penetrate the side plate  10   d  in the left-right direction. The side hole  100   c  may be formed to be long in the front-rear direction. The side hole  100   c  may be located between a right side of the top plate  10   b  and a right side of the bottom plate  10   c.    
     The mount plate  110  may include a first plate  111  and a second plate  112 . The first plate  111  may be vertically disposed on the front surface of the base W and an upper surface of the bottom plate  10   c , and may be coupled to the front surface of the base W and the upper surface of the bottom plate  10   c . The first plate  111  may be coupled to a left side of the top plate  10   b . The second plate  112  may extend obliquely in a direction away from the blower  16  from an upper end of the first plate  111 . In this case, a left side of the base  10 W, a left side of the horizontal plate  10   a , a left side of the second plate  112 , and a left side of the bottom plate  10   c  may be connected to a left side of the housing  10 H. 
     A first space  101 S may be formed between the horizontal plate  10   a  and the top plate  10   b . A vertical plate (not shown) may be connected to a front end of the horizontal plate  10   a  and a front end of the top plate  10   b , and may close a front side of the first space  101 S. The first space  101 S may communicate with the top hole  100   a.    
     A second space  102 S may be formed between the top plate  10   b  and the bottom plate  10   c . The vertical plate may be connected to a front end of the top plate  10   b  and a front end of the bottom plate  10   c , and may close the front side of the second space  102 S. The second space  102 S may communicate with the bottom hole  100   b  and the side hole  100   c.    
     For example, the bottom hole  100   b  may be opened, and the side hole  100   c  may be closed. The side hole  100   c  may be closed by a detachable cover (not shown) or may not be initially formed in the side plate  10   d.    
     In another example, the bottom hole  100   b  may be closed, and the side hole  100   c  may be opened. The bottom hole  100   b  may be closed by a detachable cover (not shown) or may not be initially formed in the bottom plate  10   c.    
     Referring to  FIGS.  3  and  4   , the gas furnace  100  may include a fuel valve  120 , a manifold  130 , a burner  140 , a heat exchanger  150 , a collect box  160 , and an inducer  170 . 
     The fuel valve  120  may supply fuel from a fuel pipe FP connected to a fuel source (not shown) to the manifold  130 , or may block the supply of the fuel to the manifold  130 . For example, the fuel may be Liquefied Natural Gas (LNG) or Liquefied Petroleum Gas (LPG). Meanwhile, by adjusting an opening degree of the fuel valve  120 , it is possible to adjust an amount of the fuel supplied to the manifold  130 . 
     The burner  140  may receive the fuel from the manifold  130 . The burner  140  may burn the fuel. When the fuel is burned, a flame and high-temperature combustion gas may be generated. For example, the burner  140  may be provided in plural. A plurality of burners  140  may be installed inside a burner box  1400 . The burner box  1400  may be installed to the left of the first plate  111  of the mount plate  110 . 
     An igniter  1401  may be mounted in the burner box  1400 , and may be adjacent to an exit of a burner located at one end of the plurality of burners  140 . For example, the igniter  1401  may be adjacent to an exit  146   e  of a sixth burner  146 , which will be described later, and may burn the fuel that has passed through the sixth burner  146  (see  FIG.  10   ). A flame formed at the exit  146   e  of the sixth burner  146  may be propagated to exits  145   e ,  144   e ,  143   e ,  142   e , and  141   e  of remaining burners  145 ,  144 ,  143 ,  142 , and  141 . The propagated flame may burn the fuel that has passed through the remaining burners  145 ,  144 ,  143 ,  142  and  141  (see  FIG.  10   ). 
     A flame detector  1402  may be mounted to the burner box  1400  and may be adjacent to an exit of a burner located at the other end of the plurality of burners  140 . For example, the flame detector  1402  may be adjacent to an exit  141   e  of a first burner  141 , which will be described later, and may detect whether a flame is formed at the exit  141   e  of the first burner  141  (see  FIG.  10   ). When the flame detector  1402  detects the flame of the first burner  141 , it is considered that a flame is formed in the remaining burners  142 ,  143 ,  144 ,  145 , and  146  as a result of combustion due to the characteristics of the flame propagation described above. 
     An air shutter  190  may be positioned between the manifold  130  and the burner  140 . The air shutter  190  may be in the shape of a box elongated in a front-rear direction as a whole. Fuel of the manifold  130  may be delivered to the burner  140  through the air shutter  190 . 
     The heat exchanger  150  may be located in the second space  102 S between the top plate  10   b  and the bottom plate  10   c . The heat exchanger  150  may provide a passage for the combustion gas. One end of the heat exchanger  150  may be coupled to the right of the first plate  111  of the mount plate  110 . The other end of the heat exchanger  150  may be spaced apart from the one end of the heat exchanger  150 , and may be coupled to the right of the first plate  111 . 
     In addition, the heat exchanger  150  may be provided in plural. The number of heat exchangers  150  may be equal to the number of burners  140 . The plurality of heat exchangers  151 ,  152 ,  153 ,  154 ,  155 , and  156  may be connected to the plurality of burners  140 , respectively. The plurality of heat exchangers  151 ,  152 ,  153 ,  154 ,  155 , and  156  may be spaced apart from each other in the front-rear direction. 
     In addition, the heat exchanger  150  may be a tubular type heat exchanger. The heat exchanger  150  may include a first tube  150   a , a bend  150   b , and a second tube  150   c . The passage of the combustion gas may be formed in the inside of the first tube  150   a , the inside of the bend  150   b , and the inside of the second tube  150   c . For example, a diameter of the first tube  150   a  may be substantially equal to a diameter of the bend  150   b  and a diameter of the second tube  150   c.    
     The first tube  150   a  may be elongated in the left-right direction. A left end of the first tube  150   a  may form the one end of the heat exchanger  150 , and may be referred to as an entry of the heat exchanger  150 . The entry of the heat exchanger  150  may communicate with the burner  140  through a first hole  111   a . Here, the first hole  111   a  may be formed to penetrate the first plate  111  in the left-right direction, and may be located between the entry of the heat exchanger  150  and the burner  140 . Meanwhile, the entry of the heat exchanger  150  may be spaced apart from the burner  140 . That is, air may be introduced into the burner  140  between the entry of the heat exchanger  150  and the burner  140 , and the air may be referred to as secondary air. 
     The second tube  150   c  may be elongated in the left-right direction. The second tube  150   c  may be spaced upward from the first tube  150   a . A left end of the second tube  150   c  may form the other end of the heat exchanger  150 , and may be referred to as an exit of the heat exchanger  150 . The exit of the heat exchanger may communicate with the inside of the collect box  160 , which will be described later, through the second hole  111   b . Here, the second hole  111   b  may be formed to penetrate the first plate  111  in the left-right direction, and may be located between the exit of the heat exchanger  150  and the collect box  160 . 
     The bend  150   b  may be connected to a right end of the first tube  150   a  and a right end of the second tube  150   c . The bend  150   b  may be convex to the right. The bend  150   b  may transfer combustion gas passing through the first tube  150   a  to the second tube  150   c . Accordingly, the combustion gas may flow to the right in the first tube  150   a , and may flow to the left in the second tube  150   b . The bend  150   b  may be referred to as a U-shaped bend. 
     Meanwhile, according to an embodiment, a bend connected to the left end of the second tube  150   c  and convex to the left, and a tube connected to the bend and disposed in parallel with the second tube  150   c  may be added. 
     The collect box  160  may be located above the burner box  1400 , and may be installed to the left of the first plate  111  of the mount plate  110 . The combustion gas passing through the heat exchanger  150  may be introduced into the inside of the collect box  160 . 
     The inducer  170  may be installed to the left of the collect box  160 . The entry of the inducer  170  may communicate with the inside of the collect box  160 . The exit  171  of the inducer  170  may be connected to an exhaust pipe  180  (see  FIG.  2   ). The inducer  170  may cause the combustion gas to flow through the heat exchanger  150 , the collector box  160 , the inducer  170 , and the exhaust pipe  180 . In addition, the inducer  170  may cause the fluid to flow through the burner  140 . The inducer  170  may be referred to as a fan, a blower, or an induced draft motor (IDM). 
     The exhaust pipe  180  (see  FIG.  2   ) may extend upward from the exit  171  of the inducer  170 . The exhaust pipe  180  may penetrate the second plate  112 , the horizontal plate  10   a , and the first long side LS1 of the mount plate  110 , and may discharge the combustion gas to the outside. The combustion gas flowing through the exhaust pipe  180  may be referred to as exhaust gas. 
     Accordingly, the air discharged from the blower  16  may pass around the heat exchanger  150  through the top hole  100   a , and may be supplied into an indoor space through the bottom hole  100   b  or the side hole  100   c . In this case, the air passing around the heat exchanger  150  may receive thermal energy from the combustion gas flowing along the heat exchanger  150 . That is, the temperature of the air may be increased while the air passes around the heat exchanger  150 . 
     Meanwhile, the gas furnace  100  may include a roll-out switch, a limit switch, a pressure switch, and the like. 
     Referring to  FIGS.  5  and  6   , the air shutter  190  may include a first housing  191  and a second housing  192 . For example, the first housing  191  may be detachably coupled to the second housing  192 . The first housing  191  and the second housing  192  may be collectively referred to as a housing  191  and  192 . 
     The first housing  191  may be elongated in the front-rear direction and may be opened upward. A plurality of lower grooves (unsigned) may be formed by being recessed downward from an upper end of a left side of the first housing  191 . 
     The second housing  191  may be elongated in the front-rear direction and may be opened downward. A plurality of upper grooves (unsigned) may be formed by being recessed upward from a lower end of a left side of the second housing  192 . 
     In addition, the upper end of the first housing  191  may contact the lower end of the second housing  192 . An inner space of the housing  191  and  192  may be formed between the first housing  191  and the second housing  192 . The inner space of the housing  191  and  192  may be referred to as an air buffer room. For example, the first housing  191  and the second housing  192  may be symmetrical to each other in the up-down direction. 
     A plurality of insertion holes h may be formed between the plurality of lower grooves and the plurality of upper grooves. A plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  may be connected to the manifold  130  and the housing  191  and  192  between the manifold  130  and the housing  191  and  192  (see  FIG.  4   ). That is, one ends of the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135  and  136  may be inserted into the manifold  130 , and the other ends of the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  may be respectively inserted into the plurality of insertion holes h1, h2, h3, h4, h5, and h6 (see  FIG.  11   ). In this case, the number of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  and the number of holes h1, h2, h3, h4, h5, and h6 may be equal to the number of burners  140 . 
     A first shell  140   a  may be elongated along the first housing  191 . The first shell  140   a  may be coupled to a right side of the first housing  191 . For example, the first shell  140   a  may be formed integrally with the first housing  191  as one body. In this case, the first shell  140   a  and the first housing  191  may be collectively referred to as a first part. In another example, the first shell  140   a  may be provided separately from the first housing  191 , and may be coupled to the first housing  191  by welding or the like. 
     In addition, the plurality of lower parts  141   a ,  142   a ,  143   a ,  144   a ,  145   a , and  146   a  may be formed by being pressed downward from an upper surface of the first shell  140   a , and may be spaced apart from each other in the front-rear direction. Meanwhile, a portion of the first shell  140   a  other than the plurality of lower parts  141   a ,  142   a ,  143   a ,  144   a ,  145   a , and  146   a  may be formed entirely flat, and may be referred to as a first flange. 
     A second shell  140   b  may be elongated along the second housing  192 . The second shell  140   b  may be coupled to a right side of the second housing  192 . For example, the second shell  140   b  may be formed integrally with the second housing  192  as one body. In this case, the second shell  140   b  and the second housing  192  may be collectively referred to as a second part. In another example, the second shell  140   b  may be provided separately from the second housing  192 , and may be coupled to the second housing  192  by welding or the like. 
     In addition, a plurality of upper parts  141   b ,  142   b ,  143   b ,  144   b ,  145   b , and  146   b  may be formed by being pressed upward from a lower surface of the second shell  140   b , and may be spaced apart from each other in the front-rear direction. Meanwhile, a portion of the second shell  140   b  other than the plurality of upper parts  141   b ,  142   b ,  143   b ,  144   b ,  145   b , and  146   b  may be formed entirely flat, and may be referred to as a second flange. 
     In addition, in the up-down direction, the second shell  140   b  may face the first shell  140   a , and the second flange may be coupled to the first flange. In this case, a plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  may include the plurality of upper parts  141   b ,  142   b ,  143   b ,  144   b ,  145   b ,  146   b  and the plurality of lower parts  141   a ,  142   a ,  143   a ,  144   a ,  145   a , and  146   a . Meanwhile, a flame propagation port (not shown) may be formed in a portion between the first flange and the second flange positioned between the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 . 
     An entry  140   i  of each of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  may be formed on a right side of the housing  191  and  192 , and may face a corresponding one of the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136 . An exit  140   e  of each of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  may be connected to an entry of a corresponding one of the plurality of heat exchangers  151 ,  152 ,  153 ,  154 ,  155 , and  156  through a plurality of first holes  111   a  (see  FIG.  4   ). 
     For example, each of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  may include a venturi portion  140   v  forming an entry  140   i  of a corresponding burner, and a head portion  140   h  forming an exit  140   e  of the corresponding burner. For example, ribs  140   r  and ribs may be formed by being recessed inward of the head portion  140   h  from a side surface of the head portion  140   h . For example, a retainer (not shown) may be inserted into the head portion  140   h  and seated on the ribs  140   r , and a flame described above or to be described later may be seated on the retainer. 
     Specifically, the first burner  141  may include a first upper part  141   b  and a first lower part  141   a , and may be spaced apart from a first nozzle  131  while facing the same. The second burner  142  may include a second upper part  142   b  and a second lower part  142   a , and may be spaced apart from the second nozzle  132  while facing the same. The third burner  143  may include a third upper part  143   b  and a third lower part  143   a , and may be spaced apart from the third nozzle  133  while facing the same. The fourth burner  144  may include a fourth upper part  144   b  and a fourth lower part  144   a , and may be spaced apart from the fourth nozzle  134  while facing the same. The fifth burner  145  may include a fifth upper part  145   b  and a fifth lower part  145   a , and may be spaced apart from the fifth nozzle  135  while facing the same. The sixth burner  146  may include a sixth upper part  146   b  and a sixth lower part  146   a , and may be spaced apart from the sixth nozzle  136  while facing the same. 
     Accordingly, fuel injected from the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135  and  136  may pass through the inner space of the housing  191  and  192  and be then supplied to the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 . 
     Referring to  FIGS.  5  and  7   , a plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  may be formed to penetrate a lower side of the first housing  191  in the up-down direction, and may be spaced apart from each other in the front-rear direction. The number of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  may be equal to the number of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 . A plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  may be formed to penetrate an upper side of the second housing  192  in the up-down direction, and may be spaced apart from each other in the front-rear direction. The number of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  may be equal to the number of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 . 
     In the up-down direction, the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  may face the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  In the left-right direction, the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  may be positioned between the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  and the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 . 
     Specifically, a first upper hole  192   a  may face a first lower hole  191   a  between the first nozzle  131  and the first burner  141 . A second upper hole  192   b  may face a second lower hole  191   b  between the second nozzle  132  and the second burner  142 . A third upper hole  192   c  may face a third lower hole  191   c  between the third nozzle  133  and the third burner  143 . A fourth upper hole  192   d  may face a fourth lower hole  191   d  between the fourth nozzle  134  and the fourth burner  144 . A fifth upper hole  192   e  may face a fifth lower hole  191   e  between the fifth nozzle  135  and the fifth burner  145 . A sixth upper hole  192   f  may face a sixth lower hole  191   f  between the sixth nozzle  136  and the sixth burner  146 . 
     The upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  and the lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  may be collectively referred to as primary holes. Meanwhile, according to an embodiment, any one of the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  and the lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  may be omitted. 
     The air shutter  190  may include a shutter assemby  193 ,  194 ,  195 , and  196 . The shutter assembly  193 ,  194 ,  195 , and  196  may include a first rack  193 , a second rack  194 , a rotary motor  195 , and a pinion  196 . 
     The first rack  193  may be elongated along the first housing  191 , and may be located inside the first housing  191 . In the front-back direction, a length L3 of the first rack  193  may be smaller than a length of the first housing  191 . In the left-right direction, a width w 3  of the first rack  193  may be smaller than a width of the first housing  191 . The first rack  193  may be coupled to the inside of the first housing  191  to be movable in the front-rear direction. For example, a first rail (not shown) may be provided inside the first housing  191 , and may guide the movement of the first rack  193 . The first rack  193  may be referred to as a lower plate. 
     In addition, a plurality of first holes  193   a ,  193   b ,  193   c ,  193   d ,  193   e , and  193   f  may be formed to penetrate the first rack  193  in the up-down direction, and may be spaced apart from each other in the front-rear direction. For example, the shapes of the first holes  193   a ,  193   b ,  193   c ,  193   d ,  193   e , and  193   f  may be substantially identical to the shapes of the lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  For example, the number of first holes  193   a ,  193   b ,  193   c ,  193   d ,  193   e , and  193   f  may be equal to the number of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f . For example, intervals between the first holes  193   a ,  193   b ,  193   c ,  193   d ,  193   e , and  193   f  may be identical to intervals between the lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f    
     The second rack  194  may be elongated along the second housing  192 , and may be located inside the second housing  192 . In the front-back direction, a length L4 of the second rack  194  may be smaller than a length of the second housing  192 . In the left-right direction, a width w 4  of the second rack  194  may be smaller than a width of the second housing  192 . The second rack  194  may be coupled to the inside of the second housing  192  to be movable in the front-rear direction. For example, a second rail (not shown) may be provided inside the second housing  191 , and may guide the movement of the second rack  194 . The second rack  194  may be referred to as an upper plate. 
     In addition, a plurality of second holes  194   a ,  194   b ,  194   c ,  194   d , and  194   e  may be formed to penetrate the second rack  194  in the up-down direction, and may be spaced apart from each other in the front and rear directions. For example, the shapes of the second holes  194   a ,  194   b ,  194   c ,  194   d , and  194   e  may be substantially identical to the shapes of the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  For example, the number of the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  of the second holes  194   a ,  194   b ,  194   c ,  194   d , and  194   e  may be one less than the number of the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f . In this case, the length L4 of the second rack  194  may be smaller than the length L3 of the first rack  193 . For example, intervals between the second holes  194   a ,  194   b ,  194   c ,  194   d , and  194   e  may be identical to intervals between the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f    
     The rotary motor  195  may provide a rotational force. The rotary motor  195  may be an electric motor, and may be capable of adjusting a rotation direction and a rotation angle. The rotary motor  195  may be located to the right of the housing  191  and  192 . A rotational shaft  195   a  of the rotary motor  195  may extend to the left from the rotary motor  195  and may pass through a shaft hole  191   g  of the housing  191  and  192 . 
     The pinion  196  may be located in the inner space of the housing  191  and  192  and may be adjacent to one end of the housing  191  and  192 . The pinion  196  may be fixed to the rotational shaft  195   a  of the rotary motor  195 . Between the first rack  193  and the second rack  194 , the pinion  196  may be engaged with a first gear tooth  193   t  of the first rack  193  and a second gear tooth  194   t  of the second rack  194 . In this case, the first gear tooth  193   t  and the second gear tooth  194   t  may be formed in the first rack  193  and the second rack  194  to correspond to movement trajectories of the first rack  193  and the second rack  194 , which will be described later. The pinion  196  may be referred to as a gear or a cogwheel. 
     Accordingly, when the rotary motor  195  is driven, the pinion  196  may be rotated in a first rotation direction Rw1 or a second rotation direction Rw2, and the first rack  193  and the second rack  194  may move in different directions. For example, when the pinion  196  is rotated in the first rotational direction Rw1, the first rack  193  may move forward and the second rack  194  may move rearward. For example, when the pinion  196  is rotated in a second rotation direction Rw2, the first rack  193  may move rearward and the second rack  194  may move forward. That is, the lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  and the upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  may be simultaneously opened or closed by the first rack  193  and the second rack  194 . 
     Referring to  FIG.  8   , a controller C may receive information from a thermostat TS, which is provided in an indoor space, through a communication part T. For example, the information received from the thermostat TS may include information such as a heating signal, a heating intensity, a desired indoor temperature, or a current indoor temperature. 
     The controller C may receive information on an operation of the gas furnace from a sensor SS. For example, the sensor SS may detect a temperature of air introduced into or discharged from the blower  16  or a temperature of air that has passed through the heat exchanger  150 . 
     The igniter  1401  and the flame detector  1402  may be electrically connected to the controller C. That is, the controller C may control the operation of the igniter  1401 , and may receive information on whether or not a flame is detected from the flame detector  1402 . 
     The blower  16 , the inducer  170 , and the fuel valve  120  may be electrically connected to the controller C. That is, the controller C may adjust a revolution per minute (RPM) of the blower  16 , an RPM of the inducer  170 , and an opening degree of the fuel valve  120 . 
     The rotary motor  195  may be electrically connected to the controller C. That is, the controller C may adjust a rotation direction and a rotation angle of the rotary motor  195 . 
     A memory M may be electrically connected to the controller C. The memory M may store information associated with an operation of the gas furnace, information associated with a control operation of the controller C, and the like, and may provide the stored information to the controller C. 
     Referring to  FIGS.  8  and  9   , the controller C may detect a required load Ld (S1). Here, a required load Ld may be a required thermal power of the gas furnace. For example, the required load Ld may be a load arbitrarily input by a user through the thermostat TS. In another example, the required load Ld may be greater as a difference (hereinafter, referred to as a temperature difference) between a desired indoor temperature input to the thermostat TS and a current indoor temperature detected by the thermocouple of the thermostat TS becomes greater. In another example, the required load Ld may be determined based on a temperature difference and temperature information on air flowing into the blower  16 , which is sensed by the sensor SS. 
     After S1, the controller C may determine whether the required load Ld is greater than a first load L1 but less than or equal to a maximum load Lm (S10). Here, the maximum load Lm may be a maximum thermal power of the gas furnace. For example, the first load L1 may be ⅓ of the maximum load Lm. 
     When the required load Ld is greater than the first load L1 but less than or equal to the maximum load Lm (Yes in S10), the controller C may perform a first operation mode (S11, S12, and S13) which will be described later with reference to  FIGS.  10  and  11   . 
     When the required load Ld is less than or equal to the first load L1 (No in S10), the controller C may perform a second operation mode (S14, S15, and S16) which will be described later with reference to  FIGS.  12  and  13   . 
     Referring to  FIGS.  9  to  11   , by adjusting a rotation direction and a rotation angle of the rotary motor  195 , the controller C (see  FIG.  8   ) may fully open the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  and the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  (S11). 
     Specifically, the plurality of first holes  193   a ,  193   b ,  193   c ,  193   d ,  193   e , and  193   f  of the first rack  193  may be aligned with the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f , respectively. In addition, the plurality of second holes  194   a ,  194   b ,  194   c ,  194   d , and  194   e  (see  FIG.  7   ) of the second rack  194  may be aligned with the second to sixth upper holes  192   a ,  192   b ,  192   c ,  192   d , and  192   f , respectively. Also, the first upper hole  192   a  may not be covered by the second rack  194 . 
     In this case, due to an inertial force and a viscous force of the fuel being injected from the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  (see  FIG.  5   ) to the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 , primary air A1 may be entrained into the inner space of the housing  191  and  192  and the burners through the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  and the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f.    
     In addition, secondary air A2 may be sucked into exits  141   e ,  142   e ,  143   e ,  144   e ,  145   e , and  146   e  of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  by the inducer  170  (see  FIG.  4   ). 
     In addition, the controller C may adjust an opening degree of the fuel valve  120  (see  FIG.  4   ) and an RPM of the inducer  170  (see  FIG.  4   ) in response to the required load Ld (S12 and S13). That is, in response to a greater required load Ld, the opening degree of the fuel valve  120  and the RPM of the inducer  170  may be increased, and in this case, a speed of fluid passing through the burner may be increased. 
     Accordingly, the primary air A1 and the fuel may pass through the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  to form a mixture, and the mixture may be combusted together with the secondary air A2. Aflame formed through the combustion may be referred to as a partially premixed flame. The partially premixed flame may have a shorter flame length than that of a diffusion flame to be described later due to the premixing characteristics, and may minimize damage to the heat exchanger due to the flame. In addition, the partially premixed flame may have a high mixing ratio of air and fuel due to the premixing characteristics, and thus, the partially premixed flame may be advantageous in reducing flame temperature and reduce thermal NOx. 
     Referring to  FIGS.  9 ,  12  and  13   , by adjusting the rotation direction and the rotation angle of the rotary motor  195 , the controller C (see  FIG.  8   ) may fully close the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  and the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  (see  FIG.  5   ) (S14). 
     Specifically, the first rack  193  may close the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f . In addition, the second rack  194  may close the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f . In this case, the primary air may be prevented from flowing into the internal space of the housing  191  and  192  and the burner. 
     In addition, the secondary air A2 may be sucked into the exits  141   e ,  142   e ,  143   e ,  144   e , and  145   e  of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  by the inducer  170  (see  FIG.  4   ). 
     Also, the controller C may adjust an opening degree of the fuel valve  120  (see  FIG.  4   ) and an RPM of the inducer  170  (see  FIG.  4   ) in response to the required load Ld (S15 and S16). That is, in response to a smaller required load Ld, the opening degree of the fuel valve  120  and the RPM of the inducer  170  may be reduced, and in this case, a speed of a fluid passing through the burner may be reduced. 
     Accordingly, the fuel may pass through the plurality of burners  141 ,  142 ,  143 ,  144 ,  145  and  146 , and may be combusted together with the secondary air A2. A flame formed through the combustion may be referred to as a diffusion flame. The diffusion flame does not have premixing characteristics, and thus, the diffusion flame may be advantageous when a relatively low thermal power is required compared to the aforementioned partially premixed flame, that is, when a velocity of a fluid passing through the burner is relatively low. In other words, at a relatively low thermal power, the stability of the diffusion flame may be higher than that of the partially premixed flame. For example, even when the required load Ld is 1/20 or more of the maximum load Lm, the diffusion flame may be stable without a problem such as flash back. That is, it is possible to secure flame stability even at a high TDR (Top Down Ratio). 
     Referring to  FIGS.  8  and  14   , when the required load Ld is greater than the first load L1 but less than the maximum load Lm (Yes in S10), the controller C may perform the first operation mode (S11, S12, and 13) which is described above with reference to  FIGS.  10  and  11   . 
     When the required load Ld is less than or equal to the first load L1 (No in S10), the controller C may determine whether the required load Ld is greater than the second load L2 but less than or equal to the first load L1 (S20). For example, the first load L1 may be ⅓ of the maximum load Lm, and the second load L2 may be ¼ or ⅛ of the maximum load Lm. 
     When the required load Ld is greater than the second load L2 but less than or equal to the first load L1 (Yes in S20), the controller C may perform a third operation mode (S21, S22, and S23) which will be described later with reference to  FIG.  15   . 
     When the required load Ld is equal to or less than the second load L2 (No in S20), the controller C may perform a second operation mode (S14, S15, and S16) which is identical to the second operation mode (S14, S15, and S16) described above with reference to  FIGS.  12  and  13   . 
     Referring to  FIGS.  14  and  15   , by adjusting a rotation direction and a rotation angle of the rotary motor  195  stepwise, the controller C (see  FIG.  8   ) may partially open the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  (see  FIG.  5   ) and the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f  (S21). 
     Specifically, the first rack  193  may partially open the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  In addition, the second rack  194  may partially open the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f.    
     In this case, due to an inertial force and a viscous force of the fuel being injected from the plurality of nozzles  131 ,  132 ,  133 ,  134 ,  135 , and  136  (see  FIG.  5   ) to the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146 , the primary air A1 may be entrained into the inner space of the housing  191  and  192  and the burners through a part of each of the plurality of lower holes  191   a ,  191   b ,  191   c ,  191   d ,  191   e , and  191   f  and a part of each of the plurality of upper holes  192   a ,  192   b ,  192   c ,  192   d ,  192   e , and  192   f.    
     In addition, the secondary air A2 may be sucked into the exits  141   e ,  142   e ,  143   e ,  144   e , and  145   e  of the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  by the inducer  170  (see  FIG.  4   ). 
     In addition, the controller C may adjust an opening degree of the fuel valve  120  (see  FIG.  4   ) and an RPM of the inducer  170  (see  FIG.  4   ) in response to the required load Ld (S22 and S23). That is, in response to a smaller required load Ld, the opening degree of the fuel valve  120  and the RPM of the inducer  170  may be reduced, and in this case, a speed of a fluid passing through the burner may be reduced. 
     Accordingly, the primary air A1 and the fuel may pass through the plurality of burners  141 ,  142 ,  143 ,  144 ,  145 , and  146  to form a mixture, and the mixture may be combusted together with the secondary air A2. Aflame formed through the combustion may be referred to as a partially premixed flame. In this case, it may be more advantageous when a relatively low thermal power is required than in the case described above with reference to  FIG.  10   . Also, in this case, it may be more advantageous in reducing a flame length and an amount of thermal NOx than the case described above with reference to  FIG.  12   . 
     Certain embodiments or other embodiments of the disclosure described above are not mutually exclusive or distinct from each other. Any or all components of the embodiments of the disclosure described above may be combined with another or combined with each other in configuration or function. 
     For example, a configuration “A” described in one embodiment of the disclosure and the drawings and a configuration “B” described in another embodiment of the disclosure and the drawings may be combined with each other. Namely, although the combination between the configurations is not directly described, the combination is possible except in the case where it is described that the combination is impossible. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of the principles of this disclosure.