Abstract: An air control assembly for a fuel burner having a combustion chamber and a nozzle includes a control device which controls the amount of air that flows into the burner and an assembly dependent on fuel pressure which actuates the control device. A fuel inlet path is provided for communicating fuel to the nozzle and a fuel return path is provided for communicating excess fuel away from the nozzle. The assembly dependent on fuel pressure includes a piston and rod device adapted for reciprocation in a piston chamber. A nozzle block is provided in which the piston chamber is defined and the nozzle is supported.

Abstract: A tube arrangement for a tube-type heat exchanger. The tube arrangement provides for the location of the tubes in the upper portion of the drum defining the combustion chamber of the heat exchanger. In one embodiment, four heat exchange tubes are provided, with two of the tubes disposed such that the axial center line of the tube lies across the horizontal center line of the heat exchanger drum, and with two tubes disposed entirely above the horizontal center line of the drum.

Abstract: A decorative gas burner system is provided with decorative gas logs which have openings or passageways to permit gas flames to be emitted therefrom which simulate the size and color of flames from wood burning logs. Gas burner means are mounted below the openings in said decorative gas log means and are provided with large hole arrays for producing long yellow or orange flames. Inverted U-shaped shield means are mounted over said gas burner means and provided with horizontal openings in the U-shape shield means and are further provided with deflector means opposite said openings in said shield means for producing long yellow gas flames with carbon monoxide emissions.

Abstract: A condensing mode furnace fired by a gun-type, power fluid fuel burner, such as an oil or gas burner, as a heat exchanger with a combustion chamber therein and communicating therewith. A duct carries the products of combustion from the heat exchanger to a thin and tube type condenser. An exhaust vent carries the products of combustion and condensate from the condenser, a drain line removing the condensate from the exhaust vent. A blower in the exhaust vent causes a flow of the products of combustion from the heat exchanger through the condenser and exhaust vent. An air passage surrounds the heat exchanger and condenser and a blower causes a flow of air serially over the condenser and heat exchanger to a hot air outlet. The furnace control initiates operation of the vent blower in response to a thermostat calling for heat in advance of operation of the burner thereby to purge on burned gases from the combustion chamber and heat exchanger.

Abstract: An apparatus for heating air using a regenerable hydrogen containing liquid fuel. The apparatus includes a hydrogen reduction catalyst, a semipermeable membrane through which hydrogen may pass and an oxidation catalyst which forms a combustion area. The hydrogen reduction catalyst is proximate to the combustion area. A displacement means transfers the hydrogen containing liquid fuel to the reduction catalyst where combustion heat decomposes the liquid fuel into hydrogen and decomposition products. The hydrogen passes through the semipermeable membrane mixes with air and is combusted at the oxidation catalyst. The decomposition products are transferred to a condensing means whereby they are condensed.

Abstract: A gas-fired condensing furnace with a corrosion resistant condensing heat exchanger. The condensing heat exchanger is formed from a flat sheet of engineering metal with a layer of polypropylene sheet material laminated thereto. Each condensing heat exchanger has a condensing flow passage of serpentine shape formed in the laminated flat sheet of engineering metal such that the polypropylene layer will be exposed to the flue gas/condensate environment to provide corrosion resistance to the metal.

Abstract: An apparatus for supplying heated air to an air stream including a first air flow duct having an inlet and an outlet, a blower for forcing air through the duct to the first duct outlet, and a second air flow duct having an inlet, an outlet, and a burner chamber between the inlet and outlet, with the second duct outlet connected to the first duct downstream of the blower for drawing atmospheric air through the second duct by air flow through the first duct. A gas burner in the burner chamber, an apertured refractory wall positioned across the second duct downstream of the burner, and a refractory liner for the inner surface of the burner chamber between the burner means and the apertured wall.

Abstract: A forced air gas fired heating device may be utilized as a stove insert for a conventional open fireplace or in an alternative embodiment may be formed with a double walled construction for use as a free standing unit. In both embodiments a gas burner adjacent a bottom portion of the housing heats an air space within the housing. A room air inlet conduit traverses back and forth across the heated air space and communicates with an air distribution chamber in an upper portion of the housing. A plurality of room air outlet conduits extend outwardly from the distribution chamber through a front wall of the housing. A heat exchanger is suspended from each of the room air outlet conduits and includes a hollow body portion in fluid communication with the associated air outlet conduit. Each of the heat exchangers has an enclosed longitudinally extending corrugated heat conductive metal plate and terminates in a bottom heat conducted metal plate deposed adjacent the gas burner.

Abstract: A vaporization burner for a heating device operated with liquid fuel, particularly a motor vehicle heating device, has a combustion pipe defining a combustion chamber, and an absorbent body arranged on a carrier, fuel being supplied to the absorbent body via said carrier. At least part of the carrier is not covered by the absorbent body, the uncovered area is provided with a through-opening. An ignition device is arranged behind the carrier and, preferably, extends into an ignition chamber, formed behind the carrier, by an ignition housing having a wall with an opening for supplying combustion air into the ignition chamber. Fuel, which has been vaporized by the absorbent body, reaches the ignition chamber via an opening in a portion of the carrier covered by the absorbent body and forms a combustible mixture. The mixture in the chamber is ignited by means of the ignition device, resulting in a pilot frame which extends through the through-opening in the uncovered area of the carrier.

Abstract: This invention provides improved gas-fired heater means for supplying heat to a space, such as a room, house, building, vehicle, or the like.

Abstract: A liquid-backed gas-fired heating system is disclosed which utilizes an infrared burner module having a helical coil wrapped concentrically thereabout. The helical coil located in the radiant zone and convective zone of the module receives heat from the hot products of combustion and transfers the heat to a circulating fluid, which in turn transfers the heat through a fan coil to the space to be heated.

Abstract: A device is disclosed for use in a combustion system to inhibit formation of oxides of nitrogen (NO.sub.x) by the combustion system thereby reducing NO.sub.x emissions from the combustion system. The device is made of a material, such as stainless steel, which is positioned at the periphery of a combustion flame produced by a burner which is part of the combustion system, to temper the combustion flame by absorbing thermal energy from the combustion flame. The device sufficiently tempers the combustion flame to limit peak combustion flame temperatures and residence times at these peak combustion flame temperatures to levels which inhibit formation of oxides of nitrogen while allowing substantially complete combustion of the fuel supplied to the burner.

Abstract: In a far-infrared radiating system, a plurality of radiating units for allowing the combustion gas to pass therethrough are connected in series to form a multi-stage series-connecting construction. The combustion gas releases its heat energy in the form of far-infrared rays when passing through each of the radiating units. The combustion gas having passed through the radiating unit decreases in temperature, and recovers its previous high temperature through combustion of a fuel which is mixed with such combustion gas before the combustion gas enters the following-stage radiating unit. Such combustion is repeated in each of the following stages so that the heat produced by combustion of the fuel is effectively radiated in the form of the far-infrared rays without making waste.

Abstract: The invention provides a compartmented gas fired heater in a cabinet-type outer stove casing. The outer stove casing has a downwardly positioned covered bottom with adjustable legs at four corners and an upwardly positioned opened top edge. A heat chamber insert having a covered bottom and an opened top is fitted inside the outer stove casing and retained so a corridor exists between all wall surfaces and the two bottoms. The top of the two sections are covered over the corridor area by a framing cover leaving the top of the heat chamber insert open as a hot air outlet. A caged outlet cover fits over the hot air outlet. Cool air is passed into the heat chamber insert through an air inlet casing. When a controlled gas burner is fired in the corridor below the bottom of the heat insert chamber, heat spirals up the corridors, is conducted through the outer stove casing and through the heat chamber insert walls and convected up through the top hot air outlet.

Abstract: Heat transfer structure for transferring heat from products of combustion to air to be conditioned in a furnace. The heat transfer structure includes an inlet portion receiving hot products of combustion from a burner and extending generally transversely to the direction of the flow of air to be conditioned by heat transfer association therewith. The heat transfer structure further includes at least three successive legs extending generally parallel to the direction of air flow. In one form, the transverse leg is disposed at the inlet portion of the air flow passages, and in a modified form, the transverse leg is disposed remotely therefrom. In the illustrated embodiments, the air moving structure is disposed in a lowermost portion of the cabinet, with the transverse inlet leg of the heat exchanger being selectively disposed lowermost or uppermost to define the two selective arrangements.

Abstract: An indirect fired air heater of the portable type and method of operating the same wherein the combustion gas flow is reversed in a combustion drum and passed through a heat exchanger between the drum and the outer casing, the heat exchanger being supported from the outer casing with the combustion drum floatingly supported therebetween.

Abstract: In the operation of a heat pipe furnace having a plurality of heat pipes and means for conducting a heated fluid in sequential heat transfer association with the heat pipes, an apparatus and method of detecting a malfunction of any one of the heat pipes of said plurality comprising means for and the steps of monitoring the temperature of the most sequentially downstream heat pipe of the plurality of heat pipes and determining whether said monitored temperature is within a preselected range of temperatures.

Abstract: A fuel burner apparatus for converting fossil fuel such as gas into heat. A cylindrical burner body is provided having an air inlet and a flame opening wherethrough flames, combustion gases and any unburned particles of fuel exit. A flame spreader apparatus is connected to the flame opening for evenly distributing the flames, combustion gases and unburned fuel particles coming out of the fuel burner. The fuel spreader apparatus includes a fuel spreader, a stem connected substantially perpendicular thereto and three leg portions connected at one end thereof to each other and at the other end thereof to the flame burner opening. The stem is connected to the meeting point of the three leg portions. A two-stage gas valve or a slow opening gas valve is provided for controlling the rate at which the fuel valve opens and allows fuel to enter the fuel burner. The fuel burner is connected to a heat exchanger which has a flue line and a blower connected to the flue line.

Abstract: A heat exchanger comprising a burner in a vertical heating chamber, having openings along its upper end to horizontally extending coils which pass through a plurality of heat transfer fins, the coils opening near the bottom edge of the assembly to a horizontally extending collector tube, open at one end and closed at the other. The open end of the collector tube opens to a vertical tubular stack through which outside air is blown past the opening to the collector tube thus creating a vacuum at that point to draw heated air from the heating chamber and through the coils where the heat is taken up by the heat transfer fins and transferred to air flowing through a hot air duct of a heating system in which the heat exchanger is placed. A blower connected in the bottom portion of the vertical stack draws outside air into the stack through an intake conduit at the bottom end and out through an exhaust conduit at the upper end of the stack.

Abstract: A forced hot air furnace having a continuously wet recuperative heat exchanger. The recuperative heat exchanger is positioned in the hot air chamber at an upward incline from the firebox to the outside flue. Inclined positioning enables heat exchanger condensate to drain counter to combustion products. Condensate is collected in a reservoir located in the firebox. Combustion products flow over the reservoir thereby becoming elevated in dew point before entering the heat exchanger. Consequently, the amount of condensation formed in the heat exchanger is substantially increased over conventional heat exchangers. Condensate will form along the entire length of the heat exchanger resulting in all wet operation. In another embodiment, continuously wet operation is achieved without a water reservoir. In still another embodiment, the continuously wet recuperative heat exchanger is coupled to the output of a non-recuperative heat exchanger.

Abstract: For a heater operated by means of liquid fuel, a vaporization burner is provided that has a large-volume active first vaporization part for the very volatile components of the fuel and a large-surface second vaporization part for the least volatile fuel components. The two vaporization parts are separated from one another by a fuel-impermeable material, such as ceramics, so that any occurring coke formations at the second passive vaporization part cannot migrate to the first vaporization part. As a result, the operating reliability and the service life of such a vaporization burner are improved.

Abstract: A furnace having a recuperative heat exchanger including apparatus for draining condensate and then flushing the exchanger with water to remove residual condensate. The recuperative heat exchanger lowers the temperature of the products of combustion from approximately 500.degree. F. to approximately 100.degree. F. thereby recovering sensible heat and heat of condensation before exhaust into the flue. Preferably, the recuperative heat exchanger functions as a preheater for forced air which is then directed past a second heat exchanger adapted to receive a circulating fluid which is heated by the combustion burner.

Abstract: An auxiliary heater for a vehicle heating system of the type having a burner projecting into a combustion chamber delimited by a combustion tube from which combustion gases emerge and are introduced into an annular space through which the combustion gases flow in an opposite direction to an exhaust outlet, the annular space being bounded peripherally by a heat exchanger containing a heat-transferring medium, such as water. In order to improve the efficiency of such an auxiliary vehicle heater and to lower the temperature of the combustion gases leaving the exhaust outlet, the cross-sectional flow-through area of the annular space is reduced in the flow direction toward the exhaust outlet. Fins are provided which project into the annular space a distance that reduces in correspondence with the reduction in the cross-sectional area of the annular space. The reduction in the cross-sectional area of the annular space may be continuous or in steps.

Abstract: A pulse combustion apparatus in which combustion air is brought into heat exchange relationship with the exhaust system of the apparatus for preheating the combustion air prior to entering the combustion chamber. In a preferred embodiment this is achieved by passing the combustion air through a space between an exhaust cushion chamber of the exhaust system and a housing which encloses the chamber.

Abstract: An improved vaporized liquid fuel combustion apparatus of the type including a cylindrical combustion chamber, a blower and a heat exchanger is disclosed. An end plate located at the upstream end of the combustion chamber is formed with an air flow guide port through which combustion air is introduced into the combustion chamber. The air flow guide port is located at a position eccentric relative to the axis of the cylindrical combustion chamber. An air guide is disposed in the area located in the proximity of the air flow guide port in such a manner to generate swirl flow in the combustion chamber. The air guide may be disposed on the wall surface of the end plate either on the side located opposite to the blower casing or on the side located opposite to the combustion chamber. The air guide is preferably formed integral with the end plate by press working.

Abstract: A recuperative furnace and method for heating wherein the recirculation air blower directs the return air upwardly first to a recuperative heat exchanger and then to a second heat exchanger operating from the heat of combustion. The flue gases are routed directly to the recuperative heat exchanger where a portion of the products of combustion condense. Accordingly, the recuperative heat exchanger not only provides sensible heat transfer from the flue gases but also recovers a portion of the latent heat of vaporization. The second heat exchanger transfers heat from a solution to the recirculation air. The solution flows through a closed loop between the second heat exchanger and a heat transfer module which includes the burner.

Abstract: A heat transfer and conditioning unit includes a casing overlying a fire chamber. An exhaust conduit is disposed within said casing inwardly of its walls having an inlet to receive heated exhaust gases and an outlet adapted to communicate with a flue to atmosphere. The exhaust conduit includes a series of pairs of opposed parallel laterally elongated plates. Inwardly directed opposed V-formed plates interconnect adjacent plates to define a series of longitudinally spaced laterally elongated venturi pasages along the length of said exhaust conduit. Said venturi passages effectively slow down the movement of the products of combustion through the exhaust conduit for increased quantities of heat transfer to the walls thereof. The walls of said exhaust conduit are spaced from the casing to define an independent fresh air heating chamber along the walls of said casing and exhaust conduit for the conductive transfer of heat to the forced fresh air passing therethrough.

Abstract: An apparatus for heating air wherein the combustion is dispersed in direct proximity to a metal hydride fuel storage means in order that the combustion heat effects the release of hydrogen from the metal hydride. The combustion area contains a catalyst and a semipermeable membrane separates the hydride fuel storage means and the combustion area. The temperature of the metal hydride is raised to effect initial release of hydrogen which passes through the semipermeable membrane, mixes with air and is combusted at the catalyst. The heat of combustion, in direct proximity to the metal hydride, perpetuates the hydrogen release.

Abstract: A forced hot air furnace having a continously wet condensing heat exchanger. The heat exchanger has an upwardly inclined first segment connected in series to a downwardly inclined second segment. Combustion products are first passed across a water reservoir thereby becoming sufficiently elevated in dew point to condense within the first segment resulting in all wet first segment operation. Condensate formed in the first segment will drain downward opposite the flow of combustion products, into the water reservoir. Since combustion products entering the second segment have been cooled to less than their dew point, the second segment will also operate in the all wet mode. Condensate flows down the second segment into a sump for transfer to the water reservoir.

Abstract: A pulse combustion apparatus in which combustion air is brought into heat exchange relationship with the exhaust system of the apparatus for preheating the combustion air prior to entering the combustion chamber. In a preferred embodiment this is achieved by passing the combustion air through a space between an exhaust cushion chamber of the exhaust system and a housing which encloses the chamber.

Abstract: A heat pipe heat transfer structure for use in a furnace wherein individual heat pipes are arranged in a series for successive heat transfer association with the hot products of combustion of the furnace. The heat transfer enclosure defines successively a combustion chamber portion, an acoustic decoupling portion, and an input heat transfer chamber portion. The heat transfer chamber portion, in turn, is divided into first and second portions. The first portion of the input heat transfer chamber portion, in the illustrated embodiment, decreases in cross sectional area in a direction away from the burner. The final portion of the input heat transfer chamber portion, in the illustrated embodiment, has a constant cross sectional area.

Abstract: A domestic forced-air furnace provided with a condensate collector downstream of air moving structure for flowing the products of combustion through the furnace. The furnace includes a secondary heat exchanger. Condensate produced therein is transferred therefrom through the air moving structure to the condensate separator. The secondary heat exchanger and air moving structure are inclined slightly to the horizontal so as to cause continuous flow of condensate therethrough not only during operation of the furnace but also subsequent thereto to assure removal of condensate from the furnace components and thereby avoid corrosive damage thereto from the condensate. The secondary heat exchanger provides the primary pressure drop in the combustion product flow path, permitting control of the furnace capacity by simple modification thereof without the need for changing other components, such as the air moving structure.

Abstract: A vaporization burner operated by means of liquid fuel for heaters, especially motor vehicle heaters. The burner has a combustion chamber, into which combustion air can be introduced in a turbulent manner under pressure. The burner also has a vaporization body made of an absorbent material that is supplied with fuel and has an essentially flat evaporation surface that faces into the combustion chamber for vaporizing the supplied fuel prior to mixing with the combustion air. Situated in the combustion chamber is an electric ignition device for igniting an initial flame. In accordance with preferred embodiments, the ignition device is an essentially flat glow-type heating element which is disposed in a plane that is adjacent and parallel to the evaporation surface of the vaporization body.

Abstract: A vaporization burner for a heater operated by means of liquid fuel, especially a motor vehicle heater. The burner is equipped with a combustion chamber and an absorbent body that can be acted upon by fuel via a fuel connection which is disposed on a carrier in the combustion chamber. In order to ensure a fast vaporization of the fuel even in the case of combustion chambers of small dimensions, the carrier is supported in the combustion chamber, so that it is protected against the dissipation of heat from it to surrounding parts.

Abstract: An infra-red heating apparatus includes a radiating surface and an adjacently located black body receiver spaced from the radiating surface. A fuel supply plenum is located adjacent to the radiating surface to provide jets of fuel along the radiating surface to be ignited thereby. Fins of heat radiating material are attached to the black body receiver and project therefrom into an air duct. Air moving through the air duct is heated as it passes over the fins.

Abstract: A hot-air heater, especially for vehicles, having a burner disposed in a housing, a fuel supply means for delivering fuel to the burner and a combustion-air fan for feeding combustion-air to said burner. Combustion-air, exhaust-gas and heating-air ducts are constructed within the housing. The housing has an opening for providing access to at least one space in which adjustable and/or replaceable parts are situated, the space being closable, relative to the outside of the heater, by means of a housing cover, and being connected to at least one of the combustion-air and exhaust-gas ducts. For reasons of safety, a combustion-air exhaust opening is provided on the pressure side of the combustion-air fan, which is blocked only when a housing cover for the housing access opening is in place, and being dimensioned in such a way that, when the combustion-air exhaust opening is not blocked, sufficient combustion-air is exhausted therethrough such that operation of the heater is not possible.

Abstract: An elongate manifold is supported in the fireplace chamber with the manifold spaced from the back of and above the fireplace floor. Gas logs are supported by a grate adjacent the manifold for heating same. A forced air blower is located behind the manifold between the manifold and the back wall of the fireplace. A vertical heat shield plate is interposed between the manifold and blower. A duct system connects the blower with the manifold and with the room served by the fireplace so as to draw air from the room, force it through the manifold and return it to the room. Thermostatic switch means limits the operation of the blower to times when the heat generated by the fireplace is substantial enough to be useful in forced air heating.

Abstract: A heater having a combustion chamber in which a burner and a heat exchanger for fluid to be heated are arranged. The burner is oblong and includes a mixing chamber with a venturishaped cross-section. A converging inlet part of the mixing chamber is connected to a feeding device for supplying air and fuel to the burner. The air and fuel are each supplied through a restriction plate of the feeding device. The restriction plate has two rows of calibrated openings so that a row of incoming air jets and a row of incoming fuel jets are formed. The row of air jets is directed against a deflecting surface incorporated in the upper wall of the inlet part for producing a whirling effect for obtaining an appropriate mixing of air and fuel. A diverging outlet part of the mixing chamber is closed by a burner plate with evenly divided ports.

Abstract: A gas fire comprises a fire bed made of refractory material with a plurality of holes therein, mounted within a combustion chamber so as to divide the combustion chamber into an upper and a lower portion, gas burners mounted so as to direct flames substantially across the upper surface of the fire bed, and a heat exchanger with a primary and secondary section, and respectively, to provide extended circulation of combustion products. Inlet of the heat exchanger is located at the rear wall of the lower portion of the combustion chamber, so that combustion products are drawn through the holes into the lower portion for entry into the heat exchanger. Simulated solid fuel elements are supported on a grid above the fire bed.

Abstract: A combustion apparatus which includes tertiary air chambers are formed on both sides of a secondary combustion chamber, with tertiary air being supplied to a combustion flame produced within the secondary combustion chamber. The secondary combustion chamber has a flow channel width greater than a width of an opening in a throttle plate provided on the upstream side thereof, thereby achieving universality with respect to enabling use of various fuel and to increase the capacity of the combustion apparatus while reducing the size thereof.

Abstract: A high efficiency induced draft clamshell type heat exchanger for use in a hot air furnace. The geometry of the heat exchanger is such that the various segments are compactly arranged to transfer heat from the fuel to the air passing over the heat exchanger surface while maintaining the discharged products of combustion at a temperature sufficiently high to prevent condensation from forming or collecting within the heat exchanger during steady state operation.

Abstract: An improvement of the space heating system delivering a composite comprising of heated outdoor air, unheated outdoor air and recirculated indoor air into a building to counter a natural infiltration of outdoor air by modulating the composite air supply delivered to the interior of a building.

Abstract: A fluid-heating apparatus comprises a ceramic burner head formed with narrow passages which alternate with one another for fuel and a combustion sustaining medium such as air, the slit-like passages opening into a combustion chamber at which combustion of the fuel/air mixture occurs. Downstream of this combustion chamber is a ceramic recuperator likewise formed with slit-like passages, the hot combustion gases traversing some of these recuperator passages while the fluid medium to be heated is passed through others of these passages so that heat exchange is effected through the thin ceramic walls supporting the slit-like passages of the ceramic recuperator.

Abstract: A combustion apparatus comprising a flame nozzle face of the burner being provided in a combustion chamber to face toward an opening of a throttled part provided within a burner frame, a mixed gas being injected into the combustion chamber from the flame nozzle at the flame nozzle face and at the same time a secondary air being supplied from both sides of the flame nozzle face, wherein optimum dimensional ranges of respective parts in combustion section are clarified and complete combustion is ensured thereby for any kind of fuel.

Abstract: A method for converting a direct fired gas heating apparatus from one having a constant volume discharge air flow characteristics to one having variable volume characteristics by the use of an internally recirculating volume discharge air flow increment.

Abstract: A forced air heater for heating a venting air stream including an outer casing, a fan for forcing the venting air stream through the casing, a combustion drum providing a combustion chamber for a burner supported within the casing, a flue gas header spaced downstream from the drum connected in separate fluid communication with the combustion chamber to accommodate evacuation of combustion gases from the chamber through the header, a passage for the venting air stream extending through the casing in heat transfer relation with the drum and header, and a plurality of vanes secured within the casing adapted to circulate a predetermined portion of the venting air stream between said drum and header.

Abstract: The sides of a heat exchanger unit are joined with perimeter flanges which are folded one over the other and then crimped tightly in such fashion as to cause adjacent portions of the perimeter to extend at different angles in different planes resulting in a scissor action therebetween effective to securely clamp the heat exchanger sides together and form a leak-proof chamber.

Abstract: A high efficiency domestic furnace incorporates means for separating and neutralizing flue gas condensate. Acidic condensate from the flue gas products of combustion is neutralized by contact with neutralizing material in a housing through which the condensate is flowed. The use of the neutralizer in connection with a high efficiency domestic furnace permits discharge of the condensate directly to the household drain. The neutralizer is arranged to be self-flushing and defines a serpentine, series flow path and is arranged to discharge the neutralized condensate as a result of the entry of additional acidic condensate at its inlet.

Abstract: Improved furnaces are described in which secondary and tertiary heat exchanges are incorporated into new and existing hot-air furnace systems for controlled cooling of hot combustion products by co-current and countercurrent heat exchanges. Hot combustion products are cooled to a temperature at which latent heat of water vapor contained in combustion gases are substantially recovered.In one embodiment of our invention, a secondary heat exchanger comprises inter alia a closed hollow annular drum concentric with and spaced from a cylindrical combustion chamber, said annular drum having an upper annulus preferably filled with randomly packed refractory material.A second embodiment of our invention comprises a closed double-annuli drum heat exchanger concentric with and spaced from a cylindrical combustion chamber.Finned tube or thermosiphon heat exchangers can be arranged sequentially with the primary heat exchanger combustion chamber to function as a secondary heat exchanger or as a tertiary heat exchanger.

Abstract: The multipurpose heating apparatus comprises a hollow and closed elongated metal casing forming a combustion chamber which is fixedly mounted within a closed insulated elongated housing, with the combustion chamber casing being spaced from the top, side walls and part of the bottom wall of the housing to define an air circulating passageway. Air supply blower means is connected to one end of the air circulating passageway while the other end of the passageway is connected to an air return passage provided in the bottom wall of the housing. The combustion chamber is divided into a solid waste fuel burning zone and into a gas or liquid fuel burning zone. Fuel burned within the combustion chamber transfers heat to the metal casing which radiates the heat into the air circulating passageway.