US 20010032641 A1
A gas-fueled heating appliance having a system for reducing the amount of undesirable combustion products released to the site in which the appliance is installed. The appliance includes a firebox partially surrounded by a heat exchanger. Ambient air is drawn into the heat exchanger below the firebox and a portion of the ambient air enters the firebox to assist in combustion, and the remaining portion travels through the heat exchanger to be heated by convection before being combined with combustion gases exiting through the top of the firebox. The heat exchanger creates a low pressure area relative to the firebox which induces a draft from the firebox into the heat exchanger and ultimately to the ambient environment through an exit provided above the firebox. A carbon monoxide catalyst element is provided in the exit passageway from the firebox to the heat exchanger to oxidize carbon monoxide into carbon dioxide and filter away airborne particulates which would otherwise be released to the ambient air.
1. A heating appliance, comprising:
a firebox having an outlet in communication with ambient air adjacent said appliance;
a gas burner disposed within said firebox, said gas burner providing a primary flame and heat source, and producing products of combustion, said products of combustion exiting said firebox through said outlet; and
a carbon monoxide catalyst element disposed in said firebox outlet, and carbon monoxide catalyst element oxidizing carbon monoxide contained within said products of combustion into carbon dioxide.
2. The heating appliance of
3. The heating appliance of
4. The heating appliance of
5. The heating appliance of
6. The heating appliance of
7. The heating appliance of
8. An unvented heating appliance located at least in part in a room and comprising:
a firebox having an inlet receiving room air and an outlet in communication with the room for exhausting combustion gases into the room;
a gas burner disposed within said firebox, said gas burner providing a primary flame and heat source, heating room air drawn into said firebox, and producing products of combustion;
a heat exchanger having an inlet, an outlet, and a plenum defining a heat exchanger airstream circuit between said heat exchanger inlet and outlet, said heat exchanger inlet located below and spaced from said heat exchanger outlet and receiving room air into said plenum, said heat exchanger outlet exhausting heated air from said heat exchanger plenum into the room, said heat exchanger partially surrounding said firebox, said firebox outlet in communication with said heat exchanger outlet, a draft resulting from said firebox being under higher pressure than said heat exchanger, said draft aspirating said products of combustion from said firebox to said heat exchanger, whereby room air is drawn through said heat exchanger airstream circuit and exhaust gases from said firebox outlet are drawn into the room air stream; and
a carbon monoxide catalyst element disposed in said firebox outlet, said carbon monoxide catalyst element oxidizing carbon monoxide contained within said products of combustion into carbon dioxide, and preventing airborne particulates from exiting said firebox.
9. The heating appliance of
10. The heating appliance of
11. The heating appliance of
12. The heating appliance of
13. The heating appliance of
14. The heating appliance of
15. The heating appliance of
16. The heating appliance of
17. A carbon monoxide catalyst element for oxidizing carbon monoxide into carbon dioxide and for use in heating appliances, said catalyst element comprising:
a plurality of planar foils manufactured from stainless steel;
a plurality of corrugated foils manufactured from stainless steel, said corrugated foils alternatingly interposed between said planar foils;
a ceramic oxide coating disposed on said plurality of planar foils and said plurality of corrugated foils; and
a precious metal coating disposed on said plurality of planar foils and said plurality of corrugated foils.
18. The carbon monoxide catalyst element of
19. A gas-fueled stove, comprising:
a firebox having an outlet in communication with ambient air adjacent said stove;
a gas burner disposed within said firebox, said gas burner providing a primary flame and heat source, and producing products of combustion, said products of combustion exiting said firebox through said outlet;
a heat exchanger partially surrounding said firebox, said heat exchanger drawing ambient air in through an entrance provided below said firebox, and exhausting convection heated air through an exit provided above said firebox;
a combustion gas circuit including an inlet communicating air to said firebox and an outlet communicating products of combustion out of said firebox; and
a carbon monoxide catalyst element disposed within said combustion gas outlet, said carbon monoxide catalyst element oxidizing carbon monoxide contained within said products of combustion into carbon dioxide, and preventing airborne particulates from exiting said stove.
20. The stove of
21. The stove of
22. The stove of
23. The stove of
24. The stove of
25. The stove of
 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.
 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.
 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 is 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.
 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 4B;
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 7D;
FIG. 7E is a perspective view of the corrugated foil member of FIG. 7A taken along lines 7E;
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 8C;
FIG. 9 is a partial side sectional view of a horizontally vented fireplace incorporating the present invention including the carbon monoxide catalyst element; and
FIG. 10 is a partial side sectional view of a vertically 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.
 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 which do pass through louvers 68, such as lint or dust, 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 at 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 tempered glass front, and 3) providing effective destruction of products of combustion. Optimal flow rate has been found to be approximately 40-60 ft3/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 off flame and loss of flickering effect, 2) temperature in firebox may be 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. Must balance the advantages and disadvantages 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 is optionally provided with blower fan 140 to draw ambient air in through inlet 42, 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 in 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.
 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. 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 bolts 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 aperture 242 and over foils 200 and 202 through catalyst element 234 as shown in FIG. 8C. Catalyst elements 234 may be cleaned by detaching bolts 230 from bolts 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 CO2 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 describer 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.