Abstract: Smoke escaping from an outdoor wood burning furnace may be effectively arrested with a smoke arresting unit. By mounting a smoke gathering manifold above the furnace door operatively connected to a vacuum source for drawing smoke discharging from the furnace chamber through an open furnace door, the gathered and arrested smoke may be discharged through a separate discharging chimney. The vacuum source may be activated when the furnace fan is switched off and the furnace door is opened for refueling.

Abstract: A clamshell heat exchanger includes a first clamshell half and a second clamshell half. When joined, the first and second clamshell halves form a passageway having an inlet and an outlet. The passageway has a height and a depth. A ratio of the height to the depth is about 0.5 or less. The heat exchanger has an efficiency of at least about 70%.

Abstract: An HVAC burner box includes a burner bank, a manifold and an air director located within an enclosure. The burner bank is oriented such that an outlet end of the burner bank is directed toward a first end of the enclosure. The manifold is located within the enclosure and adjacent an inlet end of the burner bank. The air director has a diffuser that is coupled to a side of the enclosure. The diffuser includes a plurality of openings located therethrough. The diffuser is configured to direct a first portion of a received airstream through the opening and toward the burner bank. The diffuser is further configured to send a second portion of the received airstream toward the manifold.

Abstract: A controller for a gas furnace, a computer-usable medium for implementing a method and a gas furnace are disclosed herein. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a processor configured to enable an inducer of the gas furnace at a low speed based on the heating call and ignite the gas furnace at a high fire operation when determining a low fire pressure switch of the gas furnace is open.

Abstract: HVAC systems and methods are shown which use volumetric air flow and static pressure calculations that correct for different air densities encountered at different altitudes. With respect to the volumetric airflow rate, the systems and methods disclosed herein adjust the calculation of airflow rate to better match the BTU content of de-rated natural gas used at higher elevations, and therefore they are usable in HVAC systems that combust natural gas. The adjusted static pressure calculations may be used in any type of HVAC system.

Abstract: A portable gas-fired heater comprising a housing, a burner assembly, and a carbon dioxide detector system. The housing is adapted to at least partially enclose a fuel source. The burner assembly is enclosed by the housing.

Abstract: A method controls a modulating gas furnace by monitoring a differential pressure associated with the modulating gas furnace, learning an intermediate value associated with an intermediate capacity between a minimum output capacity of the gas furnace and a maximum output capacity of the gas furnace, learning one of a high value associated with the maximum output capacity and a low value associated with a minimum output capacity, establishing an estimated operating curve using either the intermediate value and the low value or using the intermediate value and the high value, and operating the gas furnace in accordance with the estimated operating curve.

Abstract: The invention relates to a device for feeding heated water steam via a heat exchanger in a thermal engine and method for using said device.

Abstract: A draft inducer blower for high efficiency furnaces, including a blower housing which provides enhanced contact between the blower housing and the furnace collector box to reduce the flexing and vibration between the blower housing and the collector box. The blower housing includes contact structure which provides a direct abutting contact relationship between the blower housing and the collector box at least along a substantial periphery of the blower housing and/or at one or more rigid transition points on the collector box. In one embodiment, the contact structure can be part of the blower housing body and/or the blower housing cover. In another embodiment, the contact structure can be part of the collector box or furnace to which the blower housing is mounted. When fasteners secure the blower housing to the collector box, the contact structure provides a substantially integral rigid construct between the blower housing and the collector box.

Abstract: A direct gas-fired heating unit is provided which uses an axial-bladed fan for generating a main air flow through a burner unit. The burner unit has a dedicated combustion air blower supplying combustion air to the burner separate from a main air flow generated by the main fan. The burner unit includes a dedicated blower which draws a small volume of outside air as combustion air. Further, the burner unit may include bypass ports which allows for discharge of bypass air from the burner unit.

Abstract: The present invention relates generally to 90% Annual Fuel Utilization Efficiency gas or oil burning devices that depend on external air for combustion. More particularly it discloses an alternate intake apparatus for air for combustion that opens automatically when the inlet air conduit from outside is blocked or severely restricted.

Abstract: A dual fuel vent free gas heater having at least one gas burner with a plurality of gas outlet ports in an upper surface thereof. The gas outlet ports are in flow communication with at least one pilot flame burner. An adjustable fuel injector or at least two fuel injectors feed fuel to the burner providing for introduction of more than one fuel to the burner. Optionally, an oxygen detection system, manual fuel selection control valve, and/or temperature shut off control system may be incorporated into the dual fuel vent free heater.

Abstract: The invention relates to a hot-air furnace module having a furnace space, which is at least partially delimited by walls and is assigned an air-delivery device for producing an airstream and a heat-transfer device for heating the airstream. According to the invention, an incoming-air channel is provided, which is formed between the air-feed device and the furnace space for guiding the airstream delivered by the air-feed device and which is provided with first and second throttle means, which are arranged at a distance from one another in the direction of flow and are intended to even out the airstream before it flows through the furnace space. Furthermore, according to the invention a hot-air furnace is formed from hot-air furnace modules which are rotated through 180 degrees with respect to one another and are in communication with one another.

Abstract: The subject of the invention is a hot gas generator (8), particularly for a dehydration or drying unit, the generator comprising a burner or hearth (9) and being characterized in that it comprises at least one exchange circuit (10) comprising at least one pipe through which the gas to be heated flows, the pipe comprising a cool gas inlet end (11) and a hot gas discharge outlet (12), the pipe having a surface for heat exchange between the combustion gases generated by the burner or hearth (9) and the gas to be heated which flows through the pipe, the pipe also providing a physical barrier between the heated gases and the combustion gases generated by the burner or hearth. Application to producing a drying or dehydration installation.

Abstract: A burner for fuel in pellet or granular form in which the fuel has a high ash content, for example grass or hay pellets in which the ash content is 5% or more. The burner has a combustion chamber with a grate at its lower end, into which fuel and air are fed, the combustion chamber having a hot gas outlet for exhausting combustion gases. The grate is provided with a rotary member having upstanding vanes which is adapted to continually move ash or clinker on the grate through outlet apertures spaced around the grate. The grate is a generally planar, horizontal surface which is imperforate apart from the outlet apertures; air inlet ports are arranged in a circumferential wall surrounding the grate.

Abstract: An air distribution blower housing for an air handler such as a residential furnace is designed with a volute-shaped outer wall that has an exponentially increasing expansion angle in the direction of air flow through the blower housing for at least a portion of the volute-shaped outer wall length. This results in the blower housing having an enlarged air outlet opening that slows down and spreads out the air flow from the blower housing over a greater area of the furnace heat exchanger. The blower housing thereby enables less air pressure drop through the heat exchanger, which increases the efficiency of the blower motor operation. The design of the blower housing also efficiently turns the velocity head of the air flow through the housing to usable static air pressure at the housing air outlet.

Abstract: A warm air furnace capable of reliably carry out the fuel consumption conserving operation notwithstanding the condition such as the heating load is provided. The warm air furnace is equipped with an ecology operation setting unit 41, 47 for setting a saving operation function which makes the target temperature setting unit 40 set the target temperature by decreasing the same by a first predetermined temperature, after a lapse of a predetermined time after the room temperature reaches the target temperature, and for setting a moderate operation function which limits the target combustion amount when the room temperature higher than the target temperature by a second predetermined temperature or more, and an eco-operation switch 30 which is capable of setting on and off of the ecology operation setting unit 41, 47.

Abstract: A burner comprising a fuel reservoir, a primary combustion zone located at the lower end of the fuel reservoir, a secondary combustion zone located underneath the primary combustion zone, a passage providing communication between the primary and secondary combustion zones, a flue for discharging products of combustion from the secondary combustion zone, the primary combustion zone having a peripheral wall incorporating air hole means to provide combustion air to the primary combustion zone, wherein the cross-sectional area of the air hole means is substantially equal to the combined minimum cross-sectional area of the passage and the minimum cross?sectional flow area of the flue.

Abstract: A heating system has a heating unit with a combustion chamber for burning wood pellets or other pelletized fuel. The heating unit is controlled by a process control module that automatically keeps all operating functions within predetermined limits for safe, efficient and easy operation. The unit also includes a combustion air distribution assembly with a stir shaft that rotates within the combustion chamber and introduces combustion air through orifices along the length of the shaft to enhance fuel combustion. A thermo cycle plumbing assembly serves as a safety feature by preventing overheating in the event of a power failure or pump failure. Also included in the unit is a removable insulated firebox burn chamber that provides a high temperature combustion atmosphere and a heat/particulate recovery module which provides maximum heating efficiency and reduces emissions, meeting EPA requirements and contributing to a cleaner environment.

Abstract: An automatic air intake control includes a timing mechanism that regulates the amount of air entering a combustion chamber enclosure during combustion of a fuel. The amount of air is regulated to provide an efficient and clean burn of a solid fuel. The control may include a cover, an actuating assembly, and a controller. The cover is movable between open and closed positions relative to an air passage opening into the combustion chamber enclosure. The actuating assembly is coupled to the cover and configured to move the cover between the open and closed positions. The controller is coupled to the actuating member and configured to control the position of the cover through the actuating member to regulate the air intake into the combustion chamber. The controller may be a time-based device such as a timer, or may be any other device that uses inputs associated with the combustion of fuel in the combustion chamber or a user's preferences for the characteristics of combustion in combustion chamber.

Abstract: A method and apparatus for continuing the operation of a fuel fired furnace when the air supply from the blower to the furnace is interrupted by employing a combination of a ventilator and drop door, the ventilator having a power source independent of the blower.

Abstract: A warm air furnace system has a valve for controlling the flow of fuel, and a mixing component for receiving fuel from the valve and mixing the fuel with air to form an air-fuel premix. The warm air furnace system also has a burner assembly for receiving the air-fuel premix from the mixer, and an inducer for pulling the air-fuel premix through the burner assembly. The air-fuel premix drawn from the burner assembly is ignited into a flame by an ignition element. The flame transfers heat to a heat exchanger in communication with and positioned between the burner assembly and the inducer. The heat exchanger, in turn, transfers heat to air being passed over the heat exchanger by a circulation fan. The heated air passed over the heat exchanger then provides heat to a user of the furnace.

Abstract: A wood burning furnace having an enclosed combustion chamber including a top, a bottom, a back, a front and opposing side walls and a secondary combustion air admission chamber including a top, a bottom, a back, a front and opposing side walls, the bottom wall of the secondary combustion air admission chamber being arched and perforated, the bottom wall of the secondary combustion air admission chamber forming at least a portion the top wall of the combustion chamber

Abstract: A sound shield is positioned between the burner chamber of a furnace and the portion of the furnace immediately in front of the burner chamber which is typically a removable door. The removable door has slotted vents that allow air to be drawn into the burner chamber. The sound shield is positioned between the slotted vents and the burner chamber in such a manner so as to prevent substantial amounts of burner noise being produced by burning fuel from escaping through the vents. This is done without unduly restricting the flow of air through the slotted vents to the burner chamber.

Abstract: A gas-fired water heater has a combustion chamber with a bottom wall defined by a perforated flame arrestor plate forming a portion of a flow path through which combustion air may be supplied to a burner structure within the combustion chamber. During firing of the water heater a combustion air shutoff system having a heat-frangible temperature sensing structure disposed within the combustion chamber senses an undesirable temperature increase in the combustion chamber, caused by for example a partial blockage of the flow path, and responsively terminates further air flow into the combustion chamber, thereby shutting down the burner, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide.

Abstract: A gas-fired water heater has a combustion chamber with a bottom wall defined by a perforated flame arrestor plate forming a portion of a flow path through which combustion air may be supplied to a burner structure within the combustion chamber. During firing of the water heater a combustion air shutoff system having a heat-frangible temperature sensing structure disposed within the combustion chamber senses an undesirable temperature increase in the combustion chamber, caused by for example a partial blockage of the flow path, and responsively terminates further air flow into the combustion chamber, thereby shutting down the burner, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide.

Abstract: A gas-fired water heater has a combustion chamber with a bottom wall defined by a perforated flame arrestor plate forming a portion of a flow path through which combustion air may be supplied to a burner s structure within the combustion chamber. During firing of the water heater a combustion air shutoff system senses an undesirable temperature increase in the combustion chamber, caused by for example a partial blockage of the flow path, and responsively terminates further air flow into the combustion chamber, thereby shutting down the burner, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide.

Abstract: A burner box assembly for a combustion air furnace includes a back wall, opposed side walls and top and bottom walls defining an interior space for one or more burner nozzles. A combustion air inlet opening is formed in the top wall and is covered by a generally rectangular inverted channel-shaped airflow guide and baffle member. A second generally rectangular box-shaped louvered airflow guide and baffle member is mounted on the interior side of the top wall over the combustion air inlet opening for distributing the flow of combustion air into the burner box assembly and to reduce acoustic emissions from the burner box assembly through the combustion air inlet opening. The combination of the louvered baffle member and the exterior mounted baffle member provides reduced acoustic emissions from the burner box assembly as well as more evenly distributed combustion airflow into and through the burner box assembly.

Abstract: A burner system is described for burning granular pellets and similarly sized solid biomass heating fuel, e.g. wood pellets. It includes an air tight fire chamber having an exhaust outlet in an upper region thereof and a burner (10) in the bottom thereof for converting the solid fuel to fuel gases and ash in the presence of a limited air supply and combusting the gases formed. The burner comprises upright co-axial inner (12) and outer (11) cylindrical walls providing a confined central gasification/combustion chamber surrounded by an annular combustion air manifold (15). The annular combustion air manifold (15) is closed at the top and bottom with an air inlet (16) in the outer wall and a plurality of spaced aperatures (17) arranged in upward rows in the inner cylindrical wall providing air inlets from the combustion air manifold to the combustion zone of the chamber. A grate at the bottom of the gasification/combustion chamber holds the solid fuel while allowing ash to pass through the grate.

Abstract: A gas fireplace is provided having a plenum formed around at least a portion of the fireplace firebox. Room air enters the plenum and is heated by the firebox prior to venting back into the room. Two openings are provided from the outside of the fireplace housing to the plenum. The first opening allows heated air to exit the plenum, while the second opening allows cool outside air to enter the plenum. a mechanism is provided to control the amount of heated air exiting the first opening and the amount of cool air entering the second opening. By controlling the inflow and outflow through the first and second openings, respectively, the amount of the fireplace by-products generated into the room where the fireplace is located such as carbon-monoxide, nitrogen dioxide, heat and moisture are reduced.

Abstract: A damper unit is provided that is adapted to be positioned in a furnace duct line. The damper unit has a housing which is in communication with a fresh air source and a furnace system. The housing has a damper blade which is moveable between an open position which allows air flow through the housing and a closed position which prevents air flow through the housing. The blade is coupled with a solenoid so that when the solenoid is activated the blade is moved to an open position allowing air flow through the housing. Further, a fan is located in the housing adjacent the damper blade. The fan operates to move air into and out of the housing and across the damper blade when the damper blade is in its open position. In one embodiment, a pair of sealing ridges are provided on the interior of the housing.

Abstract: An electronic control for a grill, providing enhanced functionality and safety features. A hydrocarbon detector system provides an intermittently operated electro-optic device emitting photons at a wavelength which selective interacts with hydrocarbon as compared to air, associated with a detector for detecting the selective interaction and an alarm monitor for detecting an alarm state. A food temperature sensor is employed to proportionately control combustible fuel flow rate, to thereby control a food temperature profile. A communications network interface is provided to allow remote control and monitoring.

Abstract: This invention relates to a novel apparatus and method for automatically and dynamically regulating the intake of air into the combustion chamber of a heating unit such as a wood burning stove, furnace, or fireplace to ensure even and efficient burning of fuel. More particularly, this invention pertains to a method and apparatus that uses negative gas pressure in the heating unit's flue, and no additional temperature or pressure sensors, to automatically and dynamically control a damper regulating intake of air into the combustion chamber in inverse relation to changes in negative flue gas pressure. This method and apparatus are especially useful in combination with a heating unit having two combustion chambers, one chamber for combustion of solid fuel and a second chamber for further combustion of exhaust gases and other byproducts from combustion in the first chamber.

Abstract: A fuel-fired water heater has a combustion chamber disposed above a wall ucture forming a flow path for combustion air being drawn into the combustion chamber during firing of the fuel burner portion of the water heater. A combustion air shutoff system is incorporated in the water heater and functions to sense an undesirably high firing temperature in the combustion chamber and responsively shut off essentially all further air flow to the combustion chamber and thereby terminate combustion therein. In various disclosed embodiments thereof, the combustion air shutoff system includes a damper member movable between an open position in which its permits air flow through the combustion air flow path, and a closed position which it blocks essentially all further air flow through the combustion air flow path. The damper is releasably held in its open position by a eutectic metal fusible link member positioned exteriorly adjacent an exterior wall of the combustion chamber.

Abstract: A furnace having improved heat exchanger, which is particularly suitable for use in a positive pressure, direct-vented hot air furnace. The heat exchanger has a split housing construction allowing the heat exchanger to be partible into halves. Parting the heat exchanger housing of the present invention permits access to the ceramic combustion chamber disposed therein, facilitating periodic repair and replacement. The partible portions of the present heat exchanger housing are connectable using one of several available connection means, including bolted mating flanges, encircling clamps, and twisting quick-locking means. The connection between the partible portions is gasketed to provide a positive pressure seal of the connection, impeding leakage of pressurized combustion gases from within the heat exchanger to the occupied air.

Abstract: A pellet fuel burner includes a compact thermally insulated firebox for providing hot gases to a boiler, furnace or dryer. The apparatus includes a grate that includes a reciprocating arm for removing clinkers and ash from the grate. Pellet fuel feed is provided by a hopper that is isolated from the firebox by an airlock. A combustion air manifold is provided around the firebox to preheat primary and secondary combustion air.

Abstract: A wood pellet stove for efficiently burning wood pellets and especially burning pellets at low burns. The stove is accurately controlled by a control panel with a microprocessor which helps safely regulate air flow from a combustion air and exhaust gas fan. Also, the microprocessor helps control convection air flow from a convection air fan and regulate feed of wood pellets into a burn pot using a motorized auger. The microprocessor is further used to monitor inlet air temperature and exhaust gas temperature. The stove includes a stove housing with a fire box and a fire box access door in the front of the housing. The burn pot includes a burn grate and pit used for receiving and burning wood pellets. The burn pot is disposed on a fire box floor. A wood pellet hopper is disposed in the rear of the housing for holding wood pellets therein. The motorized auger is used for feeding the wood pellets into the burn pot.

Abstract: A process and apparatus for combustion of a gaseous fuel in a fireplace in which a plurality of periodic vortices are created in the airflow pattern of the combustion air prior to its mixing with the gaseous fuel, thereby producing a more natural looking, flickering flame.

Abstract: A heater including a housing, a heating assembly having a burner, and at least one of an oxygen level detection assembly adapted to distinguish between a relatively normal oxygen level, a relatively low oxygen level and relatively unsafe oxygen, a carbon monoxide sensor and a combustible gas sensor. The heater may also include an indicator adapted to produce at least one of an audible indication and a visible indication in response to a detection of a relatively low oxygen level, a detection of a predetermined level of carbon monoxide, or a detection of combustible gas.

Abstract: The invention concerns a thermostatic air flow controller. Such flow controllers may be specially useful for controlling the intake of air to a heating stove. The controller has a main air passage with a set of matching register plates which may open or close the passage according to the influence from a temperature sensing element, which is placed in a secondary air passage. The controller according to the invention has this temperature sensing element placed close to the register plates and between those plates and a heat shield which guards the temperature sensing element from the influence of the temperature in the air receiving vessel. This configuration admits a very compact construction which is specially useful for mounting the flow controller on the intake opening of a heating stove.

Abstract: A high efficiency hot air furnace transfers substantially all of the combustion heat of a clean fuel gas fire to a stream of cool recirculating air by two heat exchangers both of which are mounted in a common plenum through which cool air is recirculated by means of a blower. It differs from the conventional high efficiency furnace in that the secondary heat exchanger is a porous movable heat sink which is alternately exposed to a stream of hot combustion gas and a part of the cool air stream from the recirculating air blower.

Abstract: Apparatus for ventilating a fireplace having a combustion chamber within the interior of a building comprising an enclosure defining an air volume and a fan unit for generating a constant negative pressure region within the enclosure. A venting passage communicates the enclosure with the combustion chamber of the fireplace such that the negative pressure within the enclosure draws combustion gases from the combustion chamber into the enclosure to ventilate the fireplace. A valve is provided in the venting passage to control the flow of combustion gases to the enclosure. With this arrangement, the fan unit is operated at a constant speed to generate a constant negative pressure within the enclosure. There is no need to install an expensive variable speed fan to provide different levels of ventilation and, as long as the fan installed is sufficiently powerful to ventilate the enclosure, the valve can be used to adjust the ventilation of the fireplace combustion chamber via the enclosure.

Abstract: An inducer (40) for causing a flow of combustion air into and gases of combustion through and out of a furnace (10) of the condensing type. The inducer is intended for use, without modification of its design or size, in a series of furnaces of the same basic design but having different heating capacities and therefore different requirements for flow through the induction flow path. The furnace design is such that a given furnace is capable of operation so as to provide a flow of air to be heated that is either up, down or horizontal with only minor field modification on installation. The inducer has two discharges (43), only one of which is used in a given installation. The other discharge is blocked with a plug (61) of special configuration that can vary the output of the inducer to ensure optimum flow of combustion air into and gases of combustion through and out of the furnace.

Abstract: A low NOx burner assembly of a fuel-fired heating appliance is supplied with an air/fuel mixture having a substantially less than stoichiometric air-to-fuel ratio. The air-rich mixture is partially combusted to create primary combustion products disposed within an open inlet portion of a combustor structure having a catalytic converter operatively positioned within an open outlet portion thereof spaced apart from its open inlet portion. A flow of aspirating air is introduced into the combustor structure between the inlet and outlet portions thereof. The aspirating air mixes with the primary combustion products, cools them, and flows with them outwardly through the catalytic converter. This essentially completes the combustion of the remaining fuel within the cooled primary combustion products, and does so at a temperature not appreciably greater than the initial combustion flame temperature to thereby substantially reduce NOx emissions without the use of flame quenching techniques.

Abstract: A solid fuel burning stove of the present invention includes an internal combustion chamber, a primary air feed to the combustion chamber and a heat exchanger above and providing a secondary heated air feed to the combustion chamber. This secondary air feed raises burning temperatures and reduces pollutants from the exhaust of the stove. The heat exchanger itself has a horizontally layered substantially closed box-like construction including a heated gas outflow layer fed by the hot exhaust gases from the combustion chamber, at least one secondary air inflow layer into which secondary air is drawn from outside of the stove, a heat exchange wall between and isolating the gas outflow layer from the secondary air inflow layer and an air feed from the secondary air flow layer to the combustion chamber. The heat exchanger further includes an exhaust stack receiving opening for fitting an exhaust stack with the gas outflow layer without penetrating the secondary air inflow layer.

Abstract: A furnace having a housing, a combustion chamber within the housing, and a burner associated with the combustion chamber is provided with a sound enclosure housing including a muffler portion. The muffler portion comprises an elongated serpentine passage having an air opening at one end.

Abstract: A furnace comprises a housing, a fan or blower for moving air through housing, a burner in the housing, fuel supply means operatively connected to the burner, a heat exchanger in the housing a combustion chamber, the burner cooperating with said combustion chamber, an enclosure enclosing the heat exchanger and burner, said enclosure having an opening therein, and a damper operable to control the flow of air through said opening to the heat exchanger. The damper comprises a plate member pivotally mounted in the housing for opening and closing said opening. Preferably a drive motor opens the plate member and a spring biases the plate member closed. The damper is closed when the burner is off and is open when the burner is on. There is a circuit associated with the fuel supply means which is responsive to a predetermined open position of the plate member for permitting the flow of fuel through the fuel supply means when the plate member is open to said predetermined open position.

Abstract: A controller for automatically regulating the supply of secondary combustion air to woodstoves and small furnaces. The controller includes a movable air valve for controlling the amount of secondary air admitted into the chamber. A self powered means monitors the concentration of combustible gases and vapors and actuates the movable air valve to increase the supply of secondary air in response to increasing concentrations of the combustible gases and vapors. The self-powered means can be two fluid filled sensor bulbs, one of which has a coating of a combustion catalyst. Alternatively, the self powered means can be two metallic stripes laminated together, one of which is coated with a combustion catalyst, and when heated, causes the air valve to actuate.

Abstract: A heater for the burning of wood or other similar fuels in a fire box. The fire box has a door at the front, there being a primary air inlet to the fire box above the door. The fire box also has a secondary air inlet at the rear and a tertiary inlet at the top. The heater has a double skin so that all air for the secondary and tertiary inlets passes between the two skins so that it is pre-heated.

Abstract: A belled orifice inlet plate is provided for an induced draft combustion furnace heat exchanger of the type in which an inshot burner produces a hot gaseous combustion that is injected through an opening in the inlet plate into a combustion zone in the heat exchanger. The inlet plate has a flared collar that surrounds the opening at its periphery, and which extends a predetermined distance into the combustion zone. Preferably, the collar should have a depth on the order of one-quarter inch to one-half inch, and the flared portion should have a radius of curvature on the order of about one-quarter inch.