Patent Publication Number: US-8118590-B1

Title: Dual fuel vent free gas heater

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of, and under 35 USC §120 claims priority to and benefit from, U.S. application Ser. No. 11/684,368 filed on Mar. 9, 2007, entitled “Dual Fuel Vent Free Gas Heater,” which is currently pending naming Steve Manning as the sole inventor. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to gas heaters and, more particularly, to unvented gas heaters. 
     DESCRIPTION OF THE RELATED ART 
     Unvented gas heaters are designed to be used indoors without pipes, ducts, or other conduit to vent the heater&#39;s exhaust to the exterior atmosphere. Vent free gas heaters typically include one or more gas burners and optionally one or more ceramic containing heating elements in a housing and optionally one or more artificial logs. The gas and air mix in the heater where combustion takes place. These heaters may have a blower to force air flow through the heater providing the release of heated gases or convective heat. 
     Unvented gas heaters have been designed to be free standing, mounted on a wall, or in a decorative housing such as a vent free fireplace. The housing providing a vent free fireplace is typically substantially the size of a fireplace and has artificial logs. Some have even been designed with a glass front to provide the appearance of an enclosed fireplace. 
     The unvented heaters of the prior art are typically designed to use either natural gas or liquid propane gas as a fuel source. It is not permitted for a manufacturer to supply a conversion kit for an unvented gas heater to convert from one fuel source to another in the field. Even if such a conversion kit were permitted, as is the case with vented gas heaters, to change fuel source gas type on a heater in the field, requires the installer to change the regulator, pilot orifice and burner orifice for the alternate gas type. 
     SUMMARY OF THE INVENTION 
     A dual fuel gas burner is provided for use in a vent free heater. Embodiments of the dual fuel vent free gas burner can be used in free standing heaters, wall mount heaters, gas fireplaces, or other vent free heaters as is known in the art. A dual fuel vent free gas heater provides convective and/or radiant heat preferably to an indoor environment. The heater may be designed to use natural convective air currents and may optionally have a fan enhancing the natural convective currents within the heater. Alternatively, a fan may be used to force the gases and/or air within the heater at desired flow patterns which may be counter to natural convective forces. 
     This gas heater can be operated with multiple fuels such as liquid propane or natural gas without changing or adding components or parts. In some embodiments, an installer turns a selector valve plumbed in the product gas train. This selection sends the correct gas type to the correct fuel injector and pilot burner. Preferably, all internal plumbing connections are performed at the factory rather than onsite by the user or installer. 
     Embodiments of the gas heater can be operated on liquid propane or natural gas by connecting the fuel supply to the correct regulator on the heater. The installer or user then turns a selector valve, in selected embodiments, plumbed in the product gas train. This selection sends the correct gas type to the correct injector and pilot burner for the supply gas. Optionally, an oxygen detection system is incorporated within the heater. Advantageously, the heater is thermostatically controlled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of an embodiment of a dual fuel vent free heater showing heater components thereof assembled within a housing; 
         FIG. 2  is a cut-away view of the dual fuel vent free heater of  FIG. 1  showing an oxygen detection system; 
         FIG. 3  is a schematic view of the dual fuel vent free heater of  FIG. 1  showing flow connection of component parts; 
         FIG. 4  is a schematic view of a dual fuel vent free heater having a single multiuse injector and a thermal switch; 
         FIG. 5  is a schematic view of a dual fuel vent free heater having a dual burner configuration; 
         FIG. 6  is a schematic view of a dual fuel vent free heater having a dual burner and dual thermostatic control configuration; 
         FIG. 7  is a schematic view of a dual fuel vent free heater having a multi-positional manual control valve, a thermal switch, and a thermostatic control valve; 
         FIG. 8  is a blow-up view of the multi-positional manual control valve of  FIG. 7 ; 
         FIG. 9  is a schematic view of a dual fuel vent free heater having a multi-positional manual control valve, a thermal switch, a thermostatic control valve, and pilot burners aligned on a similar side of a burner; 
         FIG. 10  is schematic view of the dual fuel vent free heater having a first burner, a second burner, and a cross-over burner for use in a vent free fireplace unit; 
         FIG. 11  is a schematic view of a dual fuel vent free heater having a multi-positional manual control valve directly controlling the flow of fuel into the heater; 
         FIG. 12  is a schematic view of a dual fuel vent free heater having a multi-positional manual control valve, a thermal switch, a thermostatic control valve, a single fuel injector, linkage, and pilot burners aligned on opposite sides of a burner; 
         FIG. 13  is an isometric view of the multi-positional manual control valve of  FIG. 12 ; 
         FIG. 14  is a schematic view of a dual fuel vent free heater having a multi-positional manual control valve, a thermal switch, a thermostatic control, a single fuel injector, and a pilot flame burner equipped for use with two fuels; and 
         FIG. 15  is an isometric view of the pilot flame burner equipped for use with two fuels of  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description describes embodiments of a dual fuel vent free heater. In the following description, numerous specific details and options are set forth in order to provide a more thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that the invention may be practiced without such specific details or optional components and that such descriptions are merely for convenience and that such are selected solely for the purpose of illustrating the invention. As such, reference to the figures showing embodiments of the present invention is made to describe the invention and not to limit the scope of the disclosure and claims herein. 
       FIGS. 1 ,  2  and  3  show dual fuel vent free heater  100 .  FIG. 1  shows the component parts of dual fuel vent free heater  100  in a housing  180  and  FIG. 3  shows the flow diagram of heater  100 . Dual fuel vent free gas heater  100  comprises a gas burner  132  having a plurality of gas outlet ports  155  (shown in  FIG. 2 ) in an upper surface thereof. It is to be understood that outlet ports  155  may be in a side and/or lower surface of gas burner  132  and gas burner  132  may be situated vertically or angled within housing  180  and still be within the scope of this invention. Gas outlet ports  155  are in flow communication with pilot flame burners  120  and  122 . Brackets  139  hold pilot flame burners  120  and  122 , piezometric igniters  157  and  159 , and temperature sensors  152   a  and  154   a  proximate burner  132 . Piezometric igniters  157  and  159  are adjacent to pilot flame burners  122  and  120  respectively. Fuel injectors  126  and  128  are in flow communication with the interior portion of gas burner  132 . Bracket  124  holds fuel injectors  126  and  128  at an injection angle with respect to a longitudinal axis of gas burner  132  other then 0°. Injectors  126  and  128  are non-concentrically aligned with a burner venturi within burner  132 . Bracket  124  controls the angle of each injector with the axis of the burner or venturi. This angle may be varied depending on the size of the burner. Optionally, an oversized venturi may accommodate non-concentric injectors  126  and  128 . Preferably, bracket  124  has threaded apertures for accommodation of injectors having a threaded outer annular surface. Preferably, the injection angle of each injector is of the same magnitude. Fuel supply lines  134  and  136  are in flow communication with fuel injectors  126  and  128  respectively. Fuel supply line  134  and injector  126  have a composition and configuration for transporting a fuel such as natural gas or liquid propane at a desired flow rate and fuel supply line  136  and injector  128  have a composition and configuration for transporting a different fuel such as the other of natural gas or liquid propane at a desired flow rate. 
       FIG. 2  is a cutaway portion of dual fuel vent free heater  100  showing an oxygen detection system. Oxygen detection control system  131 , shown schematically in  FIG. 3 , is in electrical communication with temperature sensors  152   a  and  154   a  and thermostatic control  130  wherein thermostatic control  130  has valves controlling the flow of fuels to injectors  126  and  128  and pilot flame burners  120  and  122 . The term “thermostatic control” is used broadly throughout this specification and is not limited to controls having a temperature sensing component. Rather, the term encompasses a broad range of controls that may be implementable into a dual fuel heater, including, but not limited to, controls having a temperature sensing component as well as controls that are manually or electrically activated. Oxygen detection control system  131  sends an electrical signal to thermostatic control  130  directing thermostatic control  130  to close the valves shutting off the flow of fuel when a temperature sensor  152   a  or  154   a  indicates a temperature less than a control temperature thereby indicating a low oxygen level condition. 
     Dual fuel vent free gas heater  100  comprises two regulators  112  and  114  in flow communication with “T” connector  110  via fuel lines  148  and  150  respectively. Fuel line  146  extends from “T” connector  110  to thermostatic control  130 . Pilot line  144  leads from thermostatic control  130  to pilot control valve  118 . Injector line  142  leads from thermostatic control  130  to injector control valve  116 . Fuel lines  138  and  140  lead from pilot control valve  118  to pilot flame burners  122  and  120  respectively. Fuel lines  136  and  134  lead from injector control valve  116  to injectors  126  and  128  respectively. Control valves  118  and  116  are manually adjusted for the fuel type being connected to regulator  112  or  114 . Typically control valves  118  and  116  each have a setting for natural gas and a setting for liquid propane gas and are adjusted according to the fuel connected to regulator  112  or  114 . 
       FIG. 4  shows a schematic view of dual fuel vent free heater  400  having a single burner  132  and a thermal switch  458 . Gas burner  132  has a plurality of gas outlet ports. Fuel injector  426  is in flow communication with fuel supply line  134  and an interior of gas burner  132 . Fuel injector  426  has a manual control valve therein for controlling the flow of a fuel to burner  132 . Injector  426  has at least two settings for adjustment to alternate between at least two different fuels being fed from regulator  112  or regulator  114  through fuel supply line  134 . Fuel supply line  134  is in flow communication with thermostatic control  130 . Fuel line  140  is in flow communication with thermostatic control  130  and pilot burner  120  and has regulator  456  inline therewith. Regulators  114  and  112  each have back flow prevention systems or a plug  411  allowing a single fuel tank to be connected to either regulator leaving the other regulator without a fuel source. Regulators  112  and  114  are each in flow communication with a “T” connector via fuel lines  148  and  150  respectively. Fuel inlet line  146  extends from the “T” connector and feeds into thermostatic control  130 . Thermal switch  458  is in electrical communication with thermostatic control  130  and temperature sensor  154   a . Temperature sensor  154   a  is in proximity to pilot burner  120  and primary burner  132  as shown. Thermal switch  458  sends an electrical signal to thermostatic control  130  shutting off fuel flow to fuel supply line  134  and pilot burner supply line  140  in the event that an incorrect setting is made with injector  426  with respect to the fuel being fed to regulator  112  or  114  by measuring a high temperature condition via temperature sensor  154   a  at burner  132 . 
     In an alternative embodiment thermal switch  458  is still in electrical communication with thermostatic control  130  and temperature sensor  154   a , but does not measure a high temperature condition via temperature sensor  154   a . Rather, thermal switch  458  has internal temperature sensing and is appropriately positioned in dual fuel vent free heater  400  to measure a high temperature condition. For example, thermal switch  458  may be a normally closed switch that is opened upon expansion of one or more metals, such as a snap disc, caused by a set temperature being reached. In this alternative embodiment, communication between temperature sensor  154   a  and thermostatic control  130  is ceased when the wrong fuel type is introduced and a high temperature condition is measured via thermal switch  458 , causing the supply of gas to be shut off by thermostatic control  130 . 
       FIG. 5  shows dual fuel vent free heater  500  having a dual burner configuration. Two regulators  112  and  114  are in flow communication with a “T” connector via fuel lines  148  and  150  respectively. Fuel line  146  extends from the “T” connector to thermostatic control  130 . Pilot burner supply lines  138  and  140  lead from thermostatic control  130  to pilot flame burners  122  and  120  respectively. Fuel injector lines  134  and  136  lead from thermostatic control  130  to injectors  126  and  128  respectively. Burner  132   a  has first pilot flame burner  122  proximate gas outlet apertures therein and injector  126  proximate an axial opening. Burner  132   b  has pilot flame burner  120  proximate gas outlet apertures and injector  128  proximate an axial opening therein. 
       FIG. 6  is a schematic view of a dual fuel vent free heater  600  having a dual burner and dual thermostatic control configuration. Regulator  112  is in flow communication with thermostatic control  130   a  via fuel line  148 . Regulator  114  is in flow communication with thermostatic control  130   b  via fuel line  150 . Pilot supply line  140  leads from thermostatic control  130   a  to pilot flame burner  120  and pilot supply line  138  leads from thermostatic control  130   b  to pilot flame burner  122 . Injector supply line  134  leads from thermostatic control  130   a  to fuel injector  126 . Injector supply line  136  leads from thermostatic control  130   b  to fuel injector  128 . Burner  132   a  has pilot flame burner  120  proximate gas outlet apertures and fuel injector  126  proximate an axial opening. Burner  132   b  has pilot flame burner  122  proximate gas outlet apertures and fuel injector  128  proximate an axial opening therein. 
       FIG. 7  shows a schematic view of dual fuel vent free heater  700  having a multi-positional manual control valve  800 . Regulators  112  and  114  are in flow communication with a “T” connector via fuel lines  148  and  150  respectively. Fuel line  146  extends from the “T” connector to thermostatic control  130 . Pilot line  142  and injector line  144  lead from thermostatic control  130  to multi-positional manual control valve  800 . Multi-positional manual control valve  800  directs flow from pilot line  142  and injector line  144  to pilot supply line  140  and injector supply line  136 , or pilot supply line  138  and injector supply line  134 , or blocks the flow from pilot line  142  and injector line  144 . Burner  132  has injectors  126  and  128  held at an angle to the burner axis in proximity to the burner opening with bracket  124 . Pilot burners  120  and  122  are proximate the outer surface of burner  132  and are in flow communication with pilot supply line  140  and  138  respectively. Thermal switch  158  is in electrical communication with T/C block  756 . T/C block  756  is in electrical communication with a temperature sensor  152   a ,  154   a  proximate each pilot burner  120  and  122  and primary burner  132 , via T/C lines  154  and  152 , and thermostatic control  130 . In the event an incorrect setting is made with respect to the fuel being fed to the correct injector and pilot burner, thermal switch  158  or thermostatic control  130  shuts off the flow of gas to heater  700  by reading of a high temperature condition near burner  132 . 
       FIGS. 8A and 8B  shows a blow-up view of multi-positional manual control valve  800 . Multi-positional manual control valve  800  comprises a control block  804  and a control cylinder  802 . Control block  804  has a cylindrical aperture  850  extending from a front surface to a rear surface. The front surface of control  800  has fuel selection and cut off indicators LP, NG, and OFF. Three fuel injector apertures  820 ,  824  and  830  extend from cylindrical aperture  850  at about 90° intervals to a left side, top, and right side of control block  804 . A pilot aperture is axially aligned about cylindrical aperture  850  with each fuel injector aperture, pilot aperture  822  is axial aligned with injector aperture  820 , pilot aperture  826  is axial aligned with injector aperture  824 , and pilot aperture  828  is axial aligned with injector aperture  830 . Control cylinder  802  has an outer circumference proximate the circumference of cylindrical aperture  850  in control block  804  wherein control cylinder  802  is closely received within. Control cylinder  802  has “L” shaped flow through fuel injector aperture  812  and an axially aligned “L” shaped flow through pilot aperture  814 . Control cylinder  802  has a first, second, and third, position within the cylindrical aperture in control block  804 . The front surface of control cylinder  802  has a selection arrow pointing to an appropriate indicator on the front surface of control block  804 . At a first position, fuel injector aperture  820  and pilot aperture  822  are in flow communication with fuel injector aperture  824  and pilot aperture  826 . At a second position, as shown in  FIG. 8B , fuel injector aperture  824  and pilot aperture  826  are in flow communication with fuel injector aperture  830  and pilot aperture  828 . At the third position, one end of the “L” shaped flow through fuel injector aperture  812  and axially aligned “L” shaped flow through pilot aperture  814  are blocked by the wall of cylindrical aperture  850  in control block  804  cutting off the flow of fuel. 
       FIG. 9  shows a schematic view of dual fuel vent free heater  900 . Dual fuel vent free heater  900  comprises two regulators  112  and  114  in flow communication with a “T” connector via fuel lines  148  and  150 . Fuel line  146  extends from the “T” connector to thermostatic control  130 . A pilot line  142  and an injector line  144  lead from thermostatic control  130  to multi-positional manual control valve  800 . Multi-positional manual control valve  800  has a first, second, and third control position as indicated with LP, NG, and OFF. The first control position creates a flow communication between the pilot line  144  and injector line  142  leading from thermostatic control  130  with pilot flame burner  120  and injector  128  through pilot feed line  140  and injector feed line  136  respectively. The second control position creates a flow communication between pilot line  144  and injector line  142  leading from thermostatic control  130  with pilot flame burner  122  and injector  126  respectively. The third position cuts off fuel flow from pilot line  144  and injector line  142  leading from thermostatic control  130 . Thermal switch  935  is in electrical communication with a temperature sensor proximate pilot flame burners  120  and  122  and primary burner  132  as shown via electrical connectors  154  and  152  respectively through thermo control block (T/C block)  933 . Thermal switch  935  sends a shut off signal to thermostatic control  130  when a first set temperature is exceeded in burner  132  indicating a wrong fuel setting and cutting off the flow of fuel to heater  900 . Embodiments incorporating this safety shut-off feature and the safety shut-off feature shown in  FIG. 2  and previously described, shutting off fuel flow to the gas heater in the event a set temperature is exceeded, provide complete fuel shut-off functionality. 
       FIG. 10  shows a schematic view of dual fuel vent free heater  1000  having burner  132   a ,  132   b , and cross-over burner  171 . Such a configuration provides a blue flame burner and a yellow flame burner as is often desirable in a vent free fireplace heater. The configuration of heater  1000  is similar to the configuration of heater  900  with the addition of burners  132   b , cross-over burner  171 , two fuel line “T” connectors, and fuel injectors  126   b  and  128   b . Crossover burner  171  is in flow communication with burners  132   a  and  132   b . Burner  132   b  has fuel injectors  126   b  and  128   b  held by bracket  124   b  proximate an axial end and is situated substantially parallel burner  132   a . Fuel supply line  134   b  feeds injector  126   b  with a “T” connector in flow communication with fuel supply line  134   a . Fuel supply line  136   b  feeds injector  128   b  with a “T” connector in flow communication with fuel supply line  136   a . The statement: “Two burners or parts of burners that are in flow communication with each other” implies either that there is an opening or a connection between the two burners that allows a gas to flow from one to the other, or that some of the openings in each burner are in close proximity with each other to allow the burning gasses from one burner to ignite the gasses emanating from the other. 
       FIG. 11  is a schematic view of dual fuel vent free heater  1100  having a multi-positional manual control valve  800  directly controlling the flow of fuel into heater  1100 . The configuration of heater  1100  is similar to that of heater  900  but does not have thermostatic control  130 . Rather, fuel from either regulator  112  or regulator  114  is fed through fuel line  148  or  150 . Fuel lines  148  and  150  “T” into pilot line  142  and injector line  144  which lead directly to multi-positional manual control valve  800 . Therefore, the amount of heat produced by heater  1100  is manually controlled with multi-positional manual control valve  800  without any thermostatic control. 
       FIG. 12  shows a schematic view of dual fuel vent free heater  1200  having a multi-positional manual control valve  860 . The word “manual” in “multi-positional manual control valve” is not meant to limit multi-positional manual control valve  860  or other control valves mentioned herein to being actuated manually. Rather, as understood in the art, multi-positional manual control valve may encompass a number of control valves, such as those that are electronically or otherwise actuated. Regulators  112  and  114  are in flow communication with a “T” connector to thermostatic control  130  via fuel lines  148  and  150  respectively. Fuel line  146  extends from “T” connector to thermostatic control  130 . Pilot line  142  and injector line  144  lead from thermostatic control  130  to multi-positional manual control valve  860 . Multi-positional manual control valve  860  preferably has fuel selection indicators LP and NG that correspond to two different positions of multi-positional manual control valve  860 . Multi-positional manual control valve  860  directs flow from pilot line  142  to pilot supply line  140  or from pilot line  142  to pilot supply line  138  dependent upon whether the LP or NG position is selected. Additionally, multi-positional manual control valve  860  directs flow from injector line  144  to injector supply line  137  when the NG position is selected, while causing the flow from injector line  144  to injector supply line  137  to be restricted when LP is selected. Flow is restricted by decreasing the size of at least a portion of the orifice internal to multi-positional manual control valve  860  through which flow from injector line  144  to injector supply line  137  proceeds when LP is selected. Multi-positional manual control valve  860  may also be provided with a cut off indicator OFF that corresponds to an optional additional position of multi-positional manual control valve  860 . Such an indicator would block the flow from injector line  140  and pilot line  142  if the OFF position is selected. However, it is preferred that thermostatic control  130 , instead of multi-positional manual control valve  860 , be provided with controls for turning dual fuel vent free heater  1200  off. 
     Pilot burners  120  and  122  are proximate the outer surface of burner  132  and are in flow communication with pilot supply lines  140  and  138  respectively. Burner  132  has a single injector  427  held in proximity to the burner opening and preferably supported by bracket  125 . The flow of fuel through injector  427  is controlled by multi-positional manual control valve  860  when the appropriate fuel selection is made and no separate adjustment to fuel injector  427  is necessary when selecting a different fuel. Piezometric igniters  157  and  159  are adjacent to pilot flame burners  122  and  120  respectively. Temperature sensors  152   a  and  154   a  are proximate to pilot flame burners  122  and  120  respectively and are in electrical communication with thermal switch  558 , which is in electrical communication with thermostatic control  130 . 
     Temperature sensors  152   a  and  154   a  are positioned such that when their respective pilot flame burners are lit with a safe oxygen level present, they will be in contact with or substantially close to the pilot flame to be sufficiently heated and resultantly supply a predetermined voltage through thermal switch  558 , if it is in the closed position, to thermostatic control  130 . If this voltage is not supplied, the supply of gas to burner  132  and pilot flame burner  120  and  122  will be shut off by thermostatic control  130 . This predetermined voltage will not be supplied when an unsafe oxygen level is present, since the pilot flame will no longer be substantially close to its respective temperature sensor  152   a  or  154   a , causing temperature sensor  152   a  or  154   a  to be insufficiently heated and supply a voltage less than the predetermined voltage. In this embodiment, thermal switch  558  is preferably a normally closed switch with internal temperature sensing and is positioned in dual fuel vent free heater  1200  such that under normal heater operating conditions, it will reach a temperature that is under its set point. However, if the wrong gas type is introduced and burned in burner  132 , it will cause thermal switch  558  to heat to a temperature at or above its set point and be in the open position. This will break the communication between temperature sensors  152   a  and  154   a  and thermostatic control  130 , causing the supply of gas to injector  427  and pilot flame burners  120  and  122  to be shut off by thermostatic control  130 . The wrong gas type may be introduced in burner  132  by, among other things, feeding the wrong fuel to regulator  112  or  114 , malfunction of multi-positional manual control valve  860 , or by an incorrect setting on a fuel injector with a manual control valve. 
     Dual fuel vent free heater  1200  of  FIG. 12  is also shown with a linkage  880  that interacts with an air shutter  133  and multi-positional manual control valve  860 . Linkage  880  adjusts the position of air shutter  133  based upon the selected position of multi-positional manual control valve  860 . Air shutter  133  is located proximal to fuel injector  427  and forms part of, or is attached to, or is in close proximity to burner  132 . Adjustment of air shutter  133  allows varying amounts of air to be received through an opening in burner  132  for ideal combustion of the selected fuel. For example, in some embodiments linkage  880  could cause air shutter  133  to completely cover the opening in burner  132  when NG is selected by multi-positional manual control valve  860  and to allow the opening in burner  132  to be completely exposed when LP is selected. Dual fuel vent free heater  1200  may also be provided with a linkage (not shown) that blocks the connection to either regulator  112  or  114  dependent upon which fuel is selected by multi-positional manual control valve  860 . The linkage would prevent connection to the regulator corresponding with the fuel that is not selected, preferably by blocking or obstructing the input to the given regulator. 
     Turning to  FIG. 13 , an isometric view of a preferred embodiment of multi-positional manual control valve  860  is shown. Multi-positional manual control valve  860  has a pilot line aperture  862 , a LP pilot supply line aperture  864 , a NG pilot supply line aperture  866 , a fuel injector line aperture  870 , and a fuel injector supply line aperture  872 . Multi-positional manual control valve  860  also has an extension  882  which extends exteriorly and allows for attachment of a knob (not shown) for selection between LP and NG through rotational adjustment of internal orifices. In a first position, pilot line aperture  862  is in flow communication with LP pilot supply line aperture  864  and fuel injector line aperture  870  is in flow communication with fuel injector supply line aperture  872  and at least a portion of the internal orifice is restricted that communicates input from injector line aperture  870  to fuel injector supply line aperture  872 . In a second position, pilot line aperture  862  is in flow communication with NG pilot supply line aperture  866  and fuel injector line aperture  870  is in flow communication with fuel injector supply line aperture  872 . 
       FIG. 14  shows a schematic view of dual fuel vent free heater  1400 . Dual fuel vent free heater  1400  is similar to dual fuel vent free heater  1200 , except that it is shown without linkage  880  or air shutter  133  and has a single piezometric igniter  159 , a single temperature sensor  154   a , and a pilot flame burner equipped for use with two fuels  220 . Single temperature sensor  154   a  preferably interacts with thermostatic control  130  to provide for an oxygen detection system as previously described and additionally preferably interacts with thermal switch  558  to provide for a complete safety shutoff system as previously described. 
     Turning to  FIG. 15 , pilot flame burner equipped for use with two fuels  220  has a first fuel input orifice  222 , a second fuel input orifice  224 , and a single fuel nozzle  226 . First fuel input orifice  222  and second fuel input orifice  224  are shown in  FIG. 14  in communication with pilot supply lines  140  and  138  respectively. Since multi-positional manual control valve  860  merely redirects flow from pilot line  142  to pilot supply line  138  or pilot supply line  140 , the initial orifice size of first fuel input orifice  222  and second fuel input orifice  224  are preferably substantially the same. However, at some point before the merger of first fuel input orifice  222  and second fuel input orifice  224 , the orifice size of first fuel input orifice  222  is restricted more than the orifice size of second fuel input orifice  224 . 
     In a preferred embodiment, where multi-positional manual control valve  860  is adjustable to direct flow from pilot line  142  to pilot supply line  138  if natural gas is being used and adjustable to direct flow from pilot line  142  to pilot supply line  140  if liquid propane is being used, first fuel input orifice  222  is preferably restricted to a diameter of approximately 0.30 mm at some point before the merger of first fuel input orifice  222  and second fuel input orifice  224 , whereas the minimum orifice size of second fuel input orifice  224  is approximately 0.42 mm. Of course, when natural gas and liquid propane are the two fuels being used the actual orifice sizes may vary to some degree while still allowing for a pilot flame burner with a single fuel nozzle that can be used with two fuels. Moreover, when other fuels are being used the actual orifice sizes may vary to an even larger degree. Restricting the orifice size of first fuel input orifice  222  more than the orifice size of second fuel input orifice  224  prior to the merger of the two, causes fuel volume to be restricted and allows single fuel nozzle  226  to function with either of two fuels. Moreover, the design and placement of pilot flame burner equipped for use with two fuels  220  enables fuel volume to be properly restricted without substantially affecting fuel velocity. Therefore, a single oxygen detection system having an igniter and at least one temperature sensor proximate a single fuel nozzle can be implemented into a number of dual fuel vent free heaters using pilot flame burner equipped for use with two fuels  220 . 
     U.S. Pat. No. 5,807,098 teaches several aspects of a gas heater and a gas heater oxygen detection system and is incorporated by reference into the present document in its entirety. Using teachings from U.S. Pat. No. 5,807,098 it is clear, among other things, how more than one temperature sensor may be used with a dual fuel heater having a pilot flame burner equipped for use with two fuels  220 , or other dual fuel heaters taught herein, to provide for added functionality. Moreover, it is clear that input could be diverted to either pilot line  142  or pilot supply line  138  and resultantly first fuel input orifice  222  and second fuel input orifice  224  of pilot flame burner equipped for use with two fuels  220  through use of other valves besides multi-positional manual control valve  860 .