Abstract:
A heating appliance including a firebox having an inlet and an outlet, the firebox inlet and outlet in communication with a space containing ambient air and within which the appliance is located. A gas burner is disposed within the firebox and provides a flame, the flame supported by ambient air entering the firebox through the firebox inlet, the flame producing products of combustion which exit the firebox throught the firebox outlet. A catalyst element is in communication with the firebox outlet, and at least a portion of the products of combustion which exit the firebox through the firebox outlet are directed through the catalyst element. At least some of the products of combustion directed through the catalyst element are catalyzed, the catalyzed products of combustion being directed into the space in which the appliance is located. A plenum is in thermal communication with the firebox. Ambient air received from the space in which the appliance is located is conveyed through the plenum, the plenum having an outlet from which the air conveyed through the plenum is directed into the space in which the applicance is located. The ambient air being conveyed through the plenum is substantially out of fluid communication with the catalyzed products of combustion within the appliance.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit under Title 35, U.S.C. § 119(e) of U.S. Provisional Patent Application Serial No. 60/013,967, entitled UNVENTED GAS FIREPLACE HAVING SYSTEM FOR REDUCING UNDESIRABLE COMBUSTION PRODUCTS, filed on Mar. 22, 1996, and is a division of U.S. patent application Ser. No. 08/821,851, filed on Mar. 21, 1997, now U.S. Pat. No. 6,216,687, issued Apr. 17, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to heating appliances and, more particularly, relates to gas-fueled heating appliances, both ventless, which vent combustion gases directly into the room in which the appliance is installed and vented, which vent combustion gases to atmosphere. 
     2. Description of the Related Art 
     Gas-fueled heating appliances, such as fireplaces, stoves, and fireplace inserts, have the cleanest exhaust of any combustion process and typically include a combustion chamber, or firebox, which is provided with a source of flammable gas. The flammable gas is then combusted to provide heat and aesthetic value to the room in which the appliance is installed. The combustion typically produces carbon monoxide, carbon dioxide, water, oxygen, nitrogen, nitrogen oxide, and carbon soot, which are vented away from the fireplace and to the outside environment through a flue network or chimney. The major constituents are oxygen, nitrogen, carbon dioxide, and water with significantly lower levels of carbon monoxide, nitrogen oxides, and carbon soot. The mercaptan odorant found in gas fuel oxidizes and forms sulfuric oxides. Although such gases are vented to atmosphere, causing no serious problems in the space adjoining the appliance, increasing concerns about the environment may bring this process under heavy scrutiny and eventual regulation. 
     In certain locations, it is desirable to have an appliance capable of operating without venting to the outside environment. Therefore, gas appliances have been designed which are clean burning but “unvented” in that the gas combusts and the products of the combustion are allowed to enter the room in which the appliance is installed. With such designs, a chimney or flue network is not necessary and consequently such designs can be placed in many locations which would otherwise not be able to accommodate a vented appliance. 
     Because such designs allow combustion gases to enter the room in which the fireplace is installed, any combustion products, such as carbon monoxide, and airborne particulates, are also exhausted from the appliance directly into the room in which the appliance is located. 
     In addition, with conventional unvented appliances, the combustion gases rise within the firebox and heat the top wall of the firebox before exiting into the room in which the fireplace is installed. If the heat is not controlled, this can potentially damage the top wall of the firebox or a mantle associated therewith. 
     U.S. Pat. No. 5,054,468, issued to Moon, discloses an unvented gas-fueled fireplace heater which vents all combustion gases and airborne particulates directly into the room in which the heater is installed, but does not include any means for reducing undesirable emissions. 
     U.S. Pat. No. 5,139,011, also issued to Moon, discloses an unvented gas-fueled fireplace heater which vents combustion gases and particulates directly to the ambient room air, and further includes a sensor which detects a low oxygen level and a gas supply switch which is activated by the oxygen sensor. 
     Early attempts at ventless appliances suffer from drawbacks such as: 1) water build-up in the space, 2) acid gases, such as nitrogen oxide and sulfuric oxide, are discharged into the space potentially causing respiratory distress and corrosion in the home, 3) excessive oxygen consumption, and 4) excessive build-up of carbon monoxide levels in the space. 
     SUMMARY OF THE INVENTION 
     The present invention is for use in either vented or unvented, gas-fueled, heating appliances and includes a system for reducing the amounts of undesirable combustion products which are released into the atmosphere or space in which the appliance is installed. However, the catalyst of the present invention is particularly useful in unvented applications, where the discharge and treatment of products of combustion is even more critical. The present invention also includes a system for inducing a draft to aspirate the combustion gases from the firebox, and thereby avoid thermal damage to the firebox or mantle. 
     In particular, the present invention provides a carbon monoxide catalyst element to oxidize the carbon monoxide released by the appliance into carbon dioxide before the combustion gases are vented into the atmosphere or ambient room air. The catalyst element also serves as a filter to screen airborne particulates, such as ceramic fibers dislodged from the synthetic logs disposed within the firebox of a fireplace. 
     The carbon monoxide catalyst element is disposed within a heating appliance which includes a firebox and a heat exchanger surrounding the firebox. In one embodiment, ambient air enters the heat exchanger through an opening on the bottom front of a fireplace, below the firebox, and is divided such that a portion of the ambient air enters the firebox through openings below gas burners disposed within the firebox, and the remaining portion proceeds through the heat exchanger along a plenum below the firebox, along an adjoining plenum behind the firebox, and then along an adjoining plenum above the firebox. The air within the heat exchanger then merges with combustion air being vented from the firebox, and the recombinant air then exits the fireplace through an opening at the top front of the fireplace. 
     The front face of the fireplace is enclosed with a glass window to assure complete venting of the combustion gases through the top of the firebox and heat exchanger plenum. The carbon monoxide catalyst element is disposed in the combustion gas exit located at the top of the firebox and the openings at the top and bottom front of the fireplace are covered by a grill, louvers, mesh, or other similar device. 
     The present invention induces a draft which assists in the aspiration of the combustion gases by drawing the combustion gases from the hot air, high pressure firebox to the cooler air, low-pressure heat exchanger and ambient environment of the room in which the appliance is installed. In addition to the natural draft created by the present design, the appliance can optionally include a blower within the heat exchanger to further assist the aspiration of the combustion gases and increase the thermal output of the appliance. 
     Moreover, the draft is of a sufficient velocity to aspirate the combustion gases from the firebox at a flowrate sufficiently high to avoid structural damage to the firebox top wall, or an associated mantle. 
     One advantage of the present invention is that it substantially reduces the amount of carbon monoxide and other gases released by the appliance into the atmosphere or room in which the appliance is installed. 
     Another advantage of the present invention is that it reduces the number of airborne particulates, such as ceramic fibers, released by the appliance into the room in which the appliance is installed. 
     Another advantage of the present invention is that the combustion gases are aspirated from the firebox at a rate sufficiently fast to avoid thermal damage to the firebox or an associated mantle. 
     Another advantage of the present invention is that pollutants from sources present in the space in which the heating appliance is located are destroyed when heated in the combustion chamber and passed through the catalyst. 
     A still further advantage of the present invention is that it provides an appliance which can be installed into any site regardless of the availability of a chimney or other venting medium. 
     The present invention, in one form thereof, provides a heating appliance comprising a firebox, a gas burner, a heat exchanger, and a carbon monoxide catalyst element. The firebox includes an outlet and the gas burner which produces products of combustion. The heat exchanger partially surrounds the firebox and a draft results from the firebox being under higher pressure than the heat exchanger. The draft aspirates the products of combustion away from the firebox. The carbon monoxide catalyst element is disposed within the firebox outlet, and oxidizes carbon monoxide contained within the products of combustion into carbon dioxide and prevents airborne particulates from exiting the firebox. 
     The present invention, in another form thereof, provides a carbon monoxide catalyst element for oxidizing carbon monoxide into carbon dioxide, and comprises a plurality of planar foils, a plurality of corrugated foils, a ceramic oxide coating, and a precious metal coating. The plurality of planar foils and the plurality of corrugated foils are manufactured from stainless steel with the corrugated foils being alternatingly interposed between the planar foils. The ceramic oxide and precious metal coatings are disposed on the plurality of planar foils and the plurality of corrugated foils. 
     The present invention, in yet another form thereof, provides an unvented, gas-fueled fireplace comprising a firebox, a gas burner, a heat exchanger, and a carbon monoxide catalyst element. The firebox includes an outlet with the gas burners being disposed within the firebox and producing products of combustion. The heat exchanger partially surrounds the firebox and draws ambient air in through an entrance provided below the firebox and exhausts convection heated air through an exit provided above the firebox. A draft results from the firebox being under higher pressure than the heat exchanger, with the draft aspirating the products of combustion away from the firebox and to the ambient environment through the heat exchanger exit. The carbon monoxide catalyst element is disposed within the draft and oxidizes carbon monoxide contained within the products of combustion into carbon dioxide and prevents airborne particulates from exiting the fireplace. 
     The present invention, in still another form thereof, provides an unvented gas-fueled stove comprising a firebox, a gas burner, a heat exchanger, a combustion gas circuit, and a carbon monoxide catalyst element. The firebox includes an outlet with the gas burner being disposed within the firebox and producing products of combustion. The heat exchanger partially surrounds the firebox and draws ambient air in through an entrance provided below the firebox and exhausts convection heated air through an exit provided above the firebox. The combustion gas circuit includes an inlet communicating ambient air to the firebox and an outlet communicating products of combustion out of the firebox. The carbon monoxide catalyst element is disposed within the combustion gas outlet and oxidizes carbon monoxide contained within the products of combustion into carbon dioxide and prevents airborne particulates from exiting the stove. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side sectional view of a fireplace incorporating one embodiment of the present invention including the carbon monoxide catalyst element; 
     FIG. 2 is top view of the fireplace shown in FIG. 1 showing the placement of the carbon monoxide catalyst element; 
     FIG. 3 is right side perspective view of the fireplace shown in FIG. 1; 
     FIG. 4A is top view of the carbon monoxide catalyst element shown in FIG. 3; 
     FIG. 4B is a cutaway enlarged top view of the catalyst element of FIG. 4A taken along line  4 B; 
     FIG. 5 is an enlarged fragmentary, sectional view of the carbon monoxide catalyst element shown in FIG. 4B which shows alternating individual planar and corrugated, sinusoidal-shaped foils with a catalyst coating disposed thereon; 
     FIG. 6 is a side sectional view of an alternative embodiment of the present invention; 
     FIG. 7A is a perspective view of the carbon monoxide catalyst element being assembled; 
     FIG. 7B is a perspective view of the carbon monoxide catalyst element of FIG. 7A in a final assembled state; 
     FIG. 7C is a top view of the carbon monoxide catalyst element of FIG. 7B; 
     FIG. 7D is an enlarged, top view of the carbon monoxide catalyst element of FIG. 7C taken along lines  7 D; 
     FIG. 7E is a perspective view of the corrugated foil member of FIG. 7A taken along lines  7 E; 
     FIG. 8A is a left front perspective view of the fireplace of FIG. 1 with an alternative carbon monoxide catalyst element arrangement showing a method of assembly; 
     FIG. 8B illustrates the fireplace of FIG. 8A with the carbon monoxide catalyst element fully assembled; 
     FIG. 8C is a side sectional view of the carbon monoxide catalyst element of FIG. 8B taken along lines  8 C; 
     FIG. 9 is a partial side sectional view of a vertically vented fireplace incorporating the present invention including the carbon monoxide catalyst element; and 
     FIG. 10 is a partial side sectional view of a horizontally vented fireplace incorporating the present invention including the carbon monoxide catalyst element. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates possible embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and particularly to FIG. 1, the exemplary embodiment is shown as unvented fireplace  20  having firebox  22  partially surrounded by heat exchanger  24 . 
     Fireplace  20  includes bottom wall  26 , back wall  28 , opposing side walls  30  and  32  (FIG.  2 ), and top wall  34 . Firebox  22  includes bottom wall  36 , back wall  38 , opposing side walls  40 , and top wall  44 . Heat exchanger  24  includes bottom plenum  46  disposed between fireplace bottom wall  26  and firebox bottom wall  36 , back plenum  48  disposed between fireplace backwall  28  and firebox backwall  38 , and top plenum  50  disposed between fireplace top wall  34  and firebox top wall  44 . 
     Back plenum  48  and top plenum  50  are divided into inner passageway  52  and outer passageway  54  by room air deflector  56 . Similarly, top plenum  50  is further divided by combustion gas deflector  58 , as best shown in FIG. 1, to assist in the aspiration of combustion gases  59  from fireplace  20 . Heat shield deflector  60  is disposed above combustion product deflector  58  and room air deflector  56  to prevent the top of fireplace  20 , or an associated mantle (not shown), from becoming overheated and potentially damaged. 
     Bottom plenum  46  is provided with inlet  62 , and top plenum  50  is provided with outlet  64  to create a heat exchanger circuit, shown by flowpath arrows  66 , which commences with ambient air being drawn in through inlet  62 , continuing through back plenum  46  and top plenum  50 , and exhausting through outlet  64 . In this manner, a cold air draft is induced by introducing relatively cool space temperature air into vent inlet  62  and directing the air flow around the outside of firebox  22 . The cold air draft flow  66  exits through vent outlet  64  just above combustion gas flowpath  104 , thereby inducing draft which helps aspirate the firebox exhaust along path  104 . 
     Louvered grills  68  and  70  are provided over inlet  62  and outlet  64 , respectively, to prevent the passage of relatively large particles and objects. Any combustible products and particles, such as lint or dust, which do pass through louvers  68  and into firebox  22  are combusted within firebox  22 . To assist in the creation of a draft through heat exchanger  24 , fan assembly  72  is provided within bottom plenum  46 . In other embodiments, fireplace  20  can be provided without fan assembly  72 . Fan  72  does not run continuously, but rather a thermal disk or thermostat is placed in the unit. When the unit reaches a certain temperature, the thermostat makes a switch and fan  72  is energized. When the unit falls below a certain temperature, the thermostat breaks the switch and deenergizes the fan. This operation may be carried out by any one of many known acceptable means to achieve the desired result. 
     Firebox bottom wall  36  includes a plurality of air inlets  74  which feed air from bottom plenum  46  into firebox  22 . In the exemplary embodiment firebox  22  is provided with main burner  76  and front burner  78 , although other burner configurations are possible. Burners  76  and  78  are supplied combustible gas via a gas inlet (not shown), and with air through air inlets  74  positioned proximate gas burners  76  and  78  as shown in FIG.  1 . 
     Ceramic logs  80  are also disposed within firebox  22  atop bottom wall  36  to provide an aesthetically pleasing flame and fireplace appearance. Raised grate  82  is provided to give fireplace  20  the appearance of having a larger number of logs than are actually present, and thus reduce manufacturing costs. Glass front  84  substantially seals, in conjunction with sealing elements  86 , the front of firebox  22  such that all combustion gases  59  must exit firebox  22  through firebox outlet  88  provided in firebox top wall  44 . The average temperature of glass front  84  will be approximately 380° F. with a maximum temperature of the glass of approximately 450° F. 
     The combustion of gas at gas burners  76  and  78  produces combustion gases  59  which include, but are not limited to, carbon monoxide. To reduce the amount of carbon monoxide released to the ambient air, fireplace  20  includes carbon monoxide catalyst element  90  which is disposed in, and substantially bridges, firebox outlet  88  as shown in FIGS. 1 and 2. In vented applications, catalyst element  90  may be disposed in the flue or stack or virtually anywhere in the flow path of the products of combustion. Carbon monoxide catalyst element  90  oxidizes the carbon monoxide within combustion gases  59  into carbon dioxide before the gases are released into the ambient environment. 
     During operation, the firebox operates at a temperature approximately between 300-600° F. Because there is little or no heat generation within catalyst element  90 , the catalyst element also operates at approximately the same temperature as the firebox or more accurately the temperature of the firebox at outlet  88 . This is in sharp contrast to prior art ceramic converters used in wood burning applications in which large amounts of heat is generated by the combuster or converter. This primarily results from burning off creosote formed during the wood burning process. In the present gas burning application, no creosote is created and therefore no creosote is burned off by the catalyst element. 
     In prior art wood burning appliances, ceramic honeycomb-type combusters were used because metal was not an acceptable material. Prior art known metals were not acceptable because the metal could not operate under the high temperature conditions associated with burning off creosote. Unlike previously known metals, which had poor oxidation resistance characteristics, the new alloy high temperature stainless steel utilized in the foils of the present invention provides effective oxidation at higher temperatures. The ceramic oxide coating on the stainless steel interacts with the platinum catalyst to convert the carbon monoxide to carbon dioxide. This is in contrast to porcelinized ceramic honeycomb structures used in the wood burning applications. The porcelinized ceramic combusters virtually always crack and are typically held together by an outer skin or by framing with perforations to permit the communication of gas from the firebox through the combuster. A face plate is typically used to prevent the collapse of the porcelinized combuster and to help maintain it in its desired form. It is virtually impossible to remove and clean such a combuster because the ceramic structure is so likely to fall apart. Such problems are absent from the catalyst coated, stainless steel foils of the present invention. 
     As best shown in FIGS. 4 and 5, carbon monoxide catalyst element  90 , in the exemplary embodiment, is manufactured from a plurality of alternating corrugated stainless steel foils  92  and planar stainless steel foils  94 . The stainless steel is a ferritic stainless steel such as Alpha IV, FeCr Alloy, SR-18, or other stainless steels such as 409, 304, or 316. The new stainless steel alloys are acceptable in applications with operating temperatures as high as 1600° F. In the exemplary embodiment, foils  92  and  94  have a thickness of between 0.001 inch and 0.01 inch, preferably 0.002 inch. Foils  92  are corrugated and interposed between planar foils  94  to increase the overall surface area of catalyst element  90  exposed to the combustion gases to thereby increase the oxidizing capabilities of catalyst element  90 . The cell density associated with the configuration of the foils is preferably about 20-30 cells per square inch resulting in a porosity of approximately 90% or greater. Combustion in gas burning appliances is especially sensitive to flow obstruction. Very slight pressure drop increases, such as caused by placement of the catalyst element in the exhaust, greatly affects the amount of oxygen present and therefore the amount of carbon monoxide produced. 
     The primary design criteria in gas burning appliance designs are: 1) maintain aesthetic appearance of flickering flame, 2) provide highest temperature in firebox without compromising the tempered glass front, and 3) providing effective destruction of products of combustion. Optimal flow rate has been found to be approximately 40-60 ft 3 /minute. The pressure drop across the catalyst element affects all three of the design criteria. The greater the pressure drop the lower the flow rate, resulting in: 1) choking of flame and loss of flickering effect, 2) temperature in firebox perhaps being too great, thereby compromising the tempered glass front, and 3) more effective destruction of products of combustion. The lower the pressure drop and greater the flow rate results in: 1) enhanced flame quality, 2) good operating temperature for glass front, and 3) less effective removal of products of combustion. This would require more catalyst to achieve effective operation resulting in increased unit cost. The advantages and disadvantages must be balanced to arrive at a pressure drop/flow rate relationship that yields the most effective catalyst element configuration. 
     Ceramic oxide and precious metal coating  96  is disposed on stainless steel foils  92  and  94  as shown in FIG.  5 . In the exemplary embodiment, coating  96  is comprised of either aluminum oxide, zirconium oxide, titanium oxide, or a mixture thereof, with the precious metal being platinum or palladium or the like or a mixture thereof. The ceramic oxide coating is applied to the foils in basically two steps. First, an alumina-cerium oxide substance is colloidally dispersed and applied on the foil. Second, platinum, palladium, or a combination of the two metals at submicron levels are highly dispersed and impregnated on the foils at the surface of the ceramic oxide. 
     Carbon monoxide catalyst element  90  is disposed within catalyst element frame  98 . Frame  98  is spot welded, or otherwise attached to firebox top wall  44  in firebox outlet  88 . Frame  98  is provided with rim  100  which retains catalyst element  90  within frame  98 . The top of frame  98  is open to allow removal of catalyst element  90  for cleaning or replacement. In other embodiments, frame  98  could be provided with a screen (not shown) in lieu of rim  100  to retain catalyst element  90  within frame  98  and enable gases to pass through for oxidation. Carbon monoxide catalyst element  90  also filters out any ceramic fibers released by logs  80  as a result of gas burners  76  and  78  impinging flames  102  upon, and heating, logs  80 . 
     In operation, burners  76  and  78  combust gas drawn in through the gas inlet and create flames  102  within firebox  22 . Flames  102  within firebox  22  are fed air through air inlets  74  which allow communication between heat exchanger  24  and firebox  22 . Combustion gases  59  rise through firebox  22  and ultimately pass through firebox outlet  88  and carbon monoxide catalyst element  90  along flowpath  104 . The carbon monoxide within combustion gases  59  is converted from carbon monoxide to carbon dioxide and is exhausted from fireplace  20  through top plenum  50  and ultimately plenum outlet  64 . 
     Combustion gases  59  are drawn from firebox  22  as a result of the draft created within heat exchanger  24 . Combustion gases  59 , being heated and under pressure, are naturally drawn toward the relatively cool, low pressure heat exchanger  24  and outside ambient air. The glass cover is fixed in place as by hooks in the top of the frame and screws in the bottom, or by other suitable means. A gasket is used to help seal the firebox. This is necessary to maintain proper flow of the heated gas through the catalyst element  90 . If front cover  84  is not fixed, then the path of least resistance would be through the openings between the cover and the frame. The fixed cover also reduces the possibility of lint or other debris from entering the firebox. Because the front of firebox  22  is substantially sealed by glass front  84  and sealing elements  86 , combustion gases  59  are forced to exit firebox  22  through firebox outlet  88 . Therefore, all combustion gases  59  emanating from burners  76  and  78  pass through carbon monoxide catalyst element  90  and substantially all carbon monoxide is oxidized into carbon dioxide. In addition, any ceramic fibers released by logs  80  are prevented from exiting fireplace  20  by catalyst element  90 . In contrast to the ceramic honeycomb-type combusters associated with wood burning applications, which are characterized by a wall thickness of approximately 0.03 inch and a porosity of 50-60 percent, the catalyst element of the present invention is characterized by a porosity of approximately 90 percent or greater. This is primarily due to the significantly reduced wall thickness in the catalyst element of the present invention. 
     An alternative embodiment of the present invention is shown in FIG. 6 wherein the heating appliance is free standing stove  106 . Free standing stove  106  includes base  112 , back panel  114 , top plate  116 , glass front  118 , and firebox  108  surrounded by heat exchanger  110 . Firebox  108  includes bottom wall  120 , back wall  122 , opposing side walls  124 , and top wall  126 . Heat exchanger  110  includes bottom plenum  128  disposed between base  112  and firebox bottom wall  120 , back plenum  130  disposed between back panel  114  and firebox back wall  122 , and top plenum  132  disposed between firebox top wall  126  and stove top plate  116 . 
     As shown in FIG. 6, back plenum  130  and top plenum  132  are divided into inner passageway  134  and outer passageway  136  by deflection baffle  138 . Bottom plenum  128  is optionally provided with blower fan  140  to draw ambient air in through inlet  142 , through heat exchanger  110 , and out through outlet  144  as indicated by flowpath arrows  145 . In the embodiment shown in FIG. 6, inlet  142  is provided on the bottom back side of stove  106 , while outlet  144  is provided on the top front side of stove  106 . 
     Firebox  108  is provided with combustion air inlet  146  and firebox outlet  148 . In the embodiment shown in FIG. 6, combustion air inlet  146  is provided on the bottom back side of stove  106 , while firebox outlet  148  is provided in top wall  126 . Outlet  148  leads to stove outlet  161  such that combustion air follows flowpath  147 . Firebox  108  also includes front burner  150  and main burner  152  which are supplied gas via a gas conduit (not shown) and with air through combustion air inlet  146 . Synthetic logs  154  are provided on raised grate  156  similar to the exemplary embodiment shown in FIG.  1 . Glass front  118  substantially seals, in conjunction with sealing elements  158 , the front of firebox  108  such that all combustion gases  160  must exit firebox  108  through firebox outlet  148 . 
     Carbon monoxide catalyst element  162 , having the same design as the embodiment shown in FIG. 1 is disposed over firebox outlet  148 , and is held within frame  164  as described in reference to FIG.  1 . Although stove  106  is shown in FIG. 6 having air inlets placed at the bottom back side of stove  106  with air outlets placed on the front and top of stove  106 , it is to be understood that the inlets and outlets may be placed in other positions. It is also to be understood that top plate  116  of stove  106  can be utilized as a heating or cooking surface. 
     Catalyst  90  was tested in two fireplaces of differing designs. The first fireplace included a flue having two concentric ducts with ambient air entering through the outer duct, and hot combustion gases exiting through the inner duct. The catalyst was constructed of two 4″×41″×2″ pieces each having 32 cubic inches of volume. The temperature in the firebox was not measured directly, but the catalyst was glowing faintly red indicating a temperature of 500° to 600° C. 
     The other test fireplace drew ambient air through two holes located on the rear wall of the firebox above the burners. A single catalyst with 42.4 cubic inches of volume was installed in the exhaust flow path approximately 12 inches above the firebox in the exhaust duct. The temperature was measured at approximately 400° F. 
     Exhaust gases were pulled from the exhaust pipe at a rate of approximately three liters per minute using a diaphragm pump and the exhaust gases were then forced, under pressure, through a refrigerator device designed to separate water from combustion gases with minimum removal of carbon dioxide, nitrogen oxide, and sulphur oxide. The dry gases were then analyzed for water, oxygen, carbon dioxide, carbon monoxide, nitrogen oxide, and sulphur oxide. The gas concentrations were calculated on a wet basis. Flow rates were also monitored to assure placement of the catalyst in the exhaust flowpath did not prevent creation of an adequate draft. 
     Tests were conducted with the fireplaces in three separate modes of operation. The first test was conducted without the catalyst placed in the fireplace. The second test was conducted with the catalyst support frame inserted, and a final test was conducted with the catalyst located within the catalyst support frame. The results of the test of the first fireplace are shown in the following Table #1, and the results of the tests of the second fireplace, are shown in the following Table #2. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Fireplace 
               
             
          
           
               
                   
                 Empty 
                 Bare Support 
                 Catalyst 
               
               
                   
                   
               
             
          
           
               
                   
                 CH 4   
                 0.57 
                 0.57 
                 0.57 
               
               
                   
                 Combustion Air 
                 5.35 
                 5.35 
                 5.35 
               
               
                   
                 Supplement Air 
                 7.18 
                 4.78 
                 5.15 
               
               
                   
                 Total Air 
                 12.52 
                 10.12 
                 10.50 
               
               
                   
                 Total Flow Rate 
                 13.09 
                 10.69 
                 11.07 
               
               
                   
                 CO 2   
                 4.31% 
                 5.27% 
                 5.09% 
               
               
                   
                 H 2 O 
                 9.57% 
                 11.48% 
                 11.13% 
               
               
                   
                 O 2   
                 11.35% 
                 9.24% 
                 9.63% 
               
               
                   
                 N 2   
                 74.79% 
                 74.01% 
                 74.15% 
               
               
                   
                 CO, ppm 
                 36 
                 57 
                 3 
               
               
                   
                 NO 2 , ppm 
                 37 
                 35 
                 34 
               
               
                   
                 NO, ppm 
                 22 
                 12 
                 25 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Fireplace 
               
             
          
           
               
                   
                 Blank 
                 Support 
                 Catalyst 
               
               
                   
                   
               
             
          
           
               
                   
                 CH 4   
                 0.43 
                 0.43 
                 0.43 
               
               
                   
                 Combustion Air 
                 4.09 
                 4.09 
                 4.09 
               
               
                   
                 Supplement Air 
                 10.40 
                 9.45 
                 10.32 
               
               
                   
                 Total Air 
                 14.49 
                 13.54 
                 14.41 
               
               
                   
                 Total Flow Rate 
                 14.92 
                 13.97 
                 14.84 
               
               
                   
                 CO 2   
                 2.89% 
                 3.09% 
                 2.91% 
               
               
                   
                 H 2 O 
                 6.76% 
                 7.15% 
                 6.79% 
               
               
                   
                 O 2   
                 14.44% 
                 14.02% 
                 14.41% 
               
               
                   
                 N 2   
                 75.90% 
                 75.75% 
                 75.89% 
               
               
                   
                 CO, ppm 
                 15 
                 18 
                 1 
               
               
                   
                 NO 2 , ppm 
                 21 
                 21 
                 22 
               
               
                   
                 NO, ppm 
                 13 
                 13 
                 19 
               
               
                   
                   
               
             
          
         
       
     
     As shown in Table #1, when the bare catalyst support frame was inserted in the fireplace exhaust, the air draft was effectively choked off with a corresponding increase in carbon dioxide concentration from 4.31 percent to 5.27 percent. The carbon monoxide concentration increased from 37 parts per million to 57 parts per million. 
     However, when the catalyst was placed into the support frame, the air draft flow rate was relatively unchanged, but the carbon monoxide levels were dramatically reduced from 57 parts per million to 3 parts per million. This represents a 91.8 percent reduction in carbon monoxide emission. 
     As shown in Table #2, without a catalyst the carbon monoxide concentration was 15 to 18 parts per million. However, when the catalyst was inserted, the flow rate was approximately the same as for the empty fireplace, but the carbon monoxide levels were dramatically reduced to approximately one part per million. 
     Referring now to FIGS. 7A-7E, corrugated foil members  200  and planar foil elements  202  are alternatingly placed in catalyst element frame  204 . The foil members are sized so as to friction fit along sidewalls  206  and  208  of frame  204  during assembly. Inwardly projecting flanges  210  and  212  are provided at the base of frame of  204  to engage the outermost bottom portions of foil members  200  and  202  so as to prevent excessive downward axial movement by the foil members and to thereby hold them in place within frame  204 . An upper lip may be provided along the upper edge of frame  204  to prevent upward axial movement of foil members  200  and  202  once placed in frame  204 . At the bottom of frame  204  and along the lengths of front and back walls  214  and  216 , respectively, flanges  218  and  220  extend outwardly and engage the inside surface of ceiling  222  along the perimeter of catalyst element receiving apertures  224  and  226  (see FIG.  8 A). Catalyst  234  is attached to firebox  236  at mounting apertures  228  by mounting screws  230  as shown in FIGS. 8A-8C, discussed in detail below. 
     As opposed to sinusoidal-shaped corrugated member  92 , of FIG. 5, corrugated foil member  200 , as best shown in FIG. 7E, is semi-hexagonal along oppositely faced turns  230  and  232 . The corrugated foil members may be shaped in a variety of configurations, such as sinusoidal, hexagonal, triangular, square, etc. When selecting a shape for the corrugated foil member, the important consideration is that when coating the foil member with ceramic oxide, coating tends to build up along sharp angles in the foil. The triangular shape may be most efficient and economical because less overlapping of metal occurs and less catalyst coating is required. Planar foils  202  may be removed altogether when using corrugating foil members that are shaped so as to engage one another in a spaced apart relationship when disposed in frame  204 . An acceptable range of wall thickness for the foils, both corrugated and planar, is preferably between 0.001 and 0.01 inch with a preferred thickness of 0.002 inch. The final completed assembly of carbon monoxide catalyst element  234  is shown in FIGS. 7B and 7C. 
     FIGS. 8A-8C illustrate an alternative embodiment of the present invention in which a pair of catalyst elements  234  are mounted to the firebox, as opposed to the single catalyst element of FIG.  1 . FIGS. 8A-8C illustrate the method of assembling completed catalyst element  234  onto firebox  236  by inserting the catalysts into receiving apertures  224  and  226  provided in ceiling  222  of firebox  236 . From within the firebox, the catalyst elements are disposed axially upward into and through the apertures until support flanges  218  and  220  engage the inside surface of ceiling  222 . Mounting apertures  228  are aligned with mounting holes  238  formed in ceiling  22  adjacent apertures  224  and  226 . Mounting bolts  230 , or any other suitable fastening device or means, are received into and through apertures  228  and holes  238  and rotatably engage nuts  240  to secure catalyst elements  234  to ceiling  222  of firebox  236 . 
     The base of frame  204  is essentially hollow so that gases may flow from within firebox  236  through apertures  224  and  226  through frame  204  and over foils  200  and  202  of catalyst element  234  as shown in FIG.  8 C. Catalyst elements  234  may be cleaned by detaching bolts  230  from nuts  240  and removing the catalyst element from the firebox. Once removed, the catalyst element may be cleaned by immersing the entire catalyst element, frame, and foils, in a cleaning solution such as sodium bicarbonate or vinegar. It is preferred not to remove the individual foils once catalization has occurred. The cell density is approximately 20-30 cells per square inch in completed catalyst element  234 . Catalyst element  234  generally operates at a temperature approximately equal to the temperature in firebox  236 , typically between 300 and 600° F., because there is little or no heat generation within the converter. This is in sharp contrast to ceramic converters used in wood burning applications in which substantial heat is generated by the converter, thereby resulting in a much elevated converter operating temperature. In wood burning applications, creosote is produced and is burned off in the ceramic converters resulting in a significant increase in the operating temperature of the ceramic converter. By contrast, the gas burning applications associated with the present invention does not result in the creation of creosote. Catalyst element  234  does burn carbon monoxide in converting it to carbon dioxide. The catalyst also oxides some methane, formaldehyde, given off from insulation or carpets or out gases, from sources such as paint, polish remover, or other household objects. The catalyst burns CO to CO 2  and also some of the methane uncombusted by the burner. The catalyst also burns formaldehyde and other volatile organic compounds that may be present in the combustion air. Such volatile organic compounds come from paint, polish remover, or other household objects. 
     FIG. 9 illustrates the catalytic converter of the present invention in a vented type appliance, an example of a prior art vented appliance in which the present invention may be incorporated is illustrated in U.S. Pat. No. 5,320,086 (Beal), which is hereby incorporated into this document by reference and which is assigned to the assignee of the present invention. As shown in FIGS. 9 and 10, a concentric flue pipe assembly  242  includes a fresh air pipe  244  and exhaust pipe  246 . 
     During operation, air flow through direct vent gas fireplace  20 ′ is as follows: combustion air flows through the annular space defined between fresh air pipe  244  and exhaust pipe  246  from the ambient environment outside the building in which direct vent gas fireplace  20 ′ is installed. The combustion air flows through an air intake duct and combustion air duct  54  into the combustion chamber formed within firebox  22 ′. The flow of combustion air into the combustion chamber is represented by air flow directional arrows  104 ′. Combustion products produced in firebox  22 ′ flow through the opening defined between baffle plate  89  and firebox top wall  44 , pass over catalyst  90 , through the lower portion of exhaust pipe  246 , and are exhausted to the outside environment through the outermost portion of exhaust pipe  246 . The operation of the catalyst unit is as described hereinabove. In this manner, the expulsion of products of combustion into the atmosphere is essentially eliminated. As illustrated in FIGS. 9 and 10, respectively, the vent flue arrangement may be vertical or horizontal. The vented application does not have to be a concentric intake/exhaust configuration and may take any conventional form. 
     While the present invention has been described as having an exemplary design, the present invention can be further modified within the spirit and scope of this disclosure. Although the present invention has been described as being particularly useful in unvented applications, the present invention is nonetheless useful in vented applications as well. This application is therefore intended to encompass any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to encompass such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains, and which fall within the limits of the appended claims.