Abstract: The invention relates to a high performance burner whose performance can be controlled in a stepless manner. To this end, a premixing chamber is upstream of a burner nozzle that extends into a combustion chamber. Fuel is supplied in controllable amounts to the premixing chamber, and a mixture, in the form of an emulsion, is prepared therefrom by means of air supplied from an auxiliary air line. The air-fuel mixture thus prepared is passed to the burner nozzle which diffuses it in the combustion chamber. A high performance burner in accordance with the invention is designed for use as a heating device of high performance, like an independent heating device but, advantageously, can be employed as an exhaust gas afterburner, whereby the high performance burner is disposed in an exhaust gas line of a combustion engine, or a branch line thereto.

Abstract: The present invention discloses a method of compensating for a restricted intake in a two stage furnace. The furnace includes low and high pressure switches for determining if sufficient air is present to support low and high combustion. When the furnace operates at high combustion, the state of the high pressure switch is monitored to determine if the high pressure switch has changed state for a predetermined amount of time such as 15 seconds. The inducer fan is switched to low when insufficient air for high combustion has been indicated for such a predetermined time. If the state of the low pressure switch indicates that insufficient air is available for low combustion, then the inducer is turned on high.

Abstract: In a gas furnace designed for operation with natural gas, the use of propane as a fuel is facilitated by increasing the inducer speed by a factor which is obtained by comparing the higher inducer speed necessary to bring down the heat exchanger temperature to an acceptable level, with the original lower inducer speed that had caused the temperature to exceed the allowed limit. Provision is made for electronically applying the multiplying factor by simply operating a gas selector switch.

Abstract: In an inducted draft, fuel-fired furnace a flow restriction in the external exhaust flue is detected, and the furnace burners responsively deactivated, by a thermal sensing switch mounted in a spaced relationship with a small flow opening formed in a sensor housing externally secured to the inducer fan outlet section over a wall opening therein. During normal burner combustion product discharge flow through the exhaust flue, a small vane within the inducer fan outlet section creates a venturi therein which draws ambient air within the furnace housing across the temperature sensing switch and into the fan outlet section through the sensor housing opening. The temperature of this ambient air is below the switch set point so that continued burner operation is permitted.

Abstract: An induced draft warm air furnace employing a radiant infrared burner. The use of a radiant burner results in a very low concentration of oxides of nitrogen (NO.sub.X), in the combustion gases produced. In addition, the use of a radiant burner eliminates the combustion roar produced by other types of burners found in similar furnaces. Further, the invention allows the attainment of the advantages of a radiant burner in a furnace of otherwise standard design with only minor modification. The scope of the invention includes the use of the radiant burner within a combustion chamber which is either within the heat exchanger enclosure and joined to the heat exchanger or within a burner box mounted external to the heat exchanger enclosure but having means for the free passage of combustion gases from the combustion chamber to the heat exchanger. The use of induced draft eliminates the possibility of combustion gases leaking out of the combustion chamber or heat exchanger.

Abstract: A heater comprising a heater body containing a heating source; an air blower for forcibly blowing off heated air from the heater body into a room, the heated air being produced by heat-exchanging with the heating source; a first temperature detection element for detecting a temperature at an upper level in the room; a second temperature detection element for detecting a temperature at a lower level in the room; a sensation input means for enabling a user to input his or her sensation corresponding to an actual room temperature; means for determining heating capability of the heating source based on the difference between the temperature detected by the first temperature detection element and a first set temperature; means for changing the outlet area and/or the air volume of the heated air based on the difference between the temperature detected by the second temperature detection element and a second set temperature lower than the first set temperature to determine the blow-off speed and/or the air volume of

Abstract: A direct gas-fired heating and ventilating system for industrial and commercial buildings and the like comprises a direct gas-fired burner, fresh air dampers, fresh air bypass dampers and recirculation dampers.

Abstract: Embodiments of gas-fired appliances which generate sufficient electricity to be self-powered include water heaters, space heaters, air conditioning units, and electric power and steam cogeneration systems. In such apparatus, gas is burned in a porous ceramic surface combustion burner. The high temperature surface of the burner includes a narrow band quantum emitting substance such as a rare earth metal oxide and preferably ytterbium oxide. Relatively shorter wavelength radiation from this quantum emitting surface illuminates photovoltaic cells having an absorption spectrum matched to the emission spectrum of the burner surface for generating sufficient electricity for powering the appliance. An infrared absorbing filter removes relatively longer wavelength radiation which would otherwise heat the photovoltaic cells. The cells are cooled, preferably by a portion of the utility fluid heated by the appliance.

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: An automatic device for controlling the supply of fuel to a heater which includes magnetic device units operatively associated with on/off switches, respectively, and a thermostat operatively connected to the switches, whereby one of the switches is actuated to the off position by the sensing of the thermostat for a period time of a higher room temperature than a predetermined thermostat temperature. Also, upon the off position of the source of electric power, the fuel supply automatically puts out the fire.

Abstract: A heating appliance has a burner of the type having full premixing and forced draught and a mixing chamber to which an air supply line and a fuel supply are connected. The mixing chamber has a burner plate which is provided with apertures and which adjoins a combustion chamber in which a heat exchanger is disposed some distance from the burner plate and is passed through by the medium to be heated. A flue is connected to the combustion chamber. The effective heat transfer of the flue gases to the heat exchanger is varied depending on the load on the heating appliance.

Abstract: A microprocessor control determines, in the course of initiating a heating cycle, whether the blower is operating in the continuous mode, and if it is, the control prompts the blower to be turned off prior to the ignitor being turned on. In this way, the blower and ignitor are never on at the same time and the instantaneous total current draw is limited to thereby reduce the occurrence of burned out fuses or circuit breaker trips.

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 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 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 fuel supply system for a fuel spray combustor nozzle of a portable heater including a pump connected to the fuel spray combustor nozzle on the high pressure side thereof and alternatively connectable on the low pressure side to an on-board fuel chamber storage means or to an off-board storage supply through an actuable valve and solenoid system connected by fluid piping, valves and fittings extending between the on-board nozzle, pump, and storage chambers and toward off-board supply.

Abstract: The control system of an induced draft furnace includes a provision for turning on the inducer motor when a flame is sensed outside of the normal sequence of a heating operation. In particular, if the thermostat is in the off position when a flame is sensed, the inducer motor is turned on to ensure that sufficient combustion air is provided to the burner so as to forestall the occurrence of flame roll outs in the event that the gas valve is stuck in a closed position.

Abstract: A gas burning furnace is disclosed with a sealed and vented gas control valve. Sealing the gas control valve in an enclosure shields the control valve from the external environment. By venting the enclosure to the furnace pilot light, any gas leaking from the gas control valve into the enclosure is conducted to and ignited by the pilot light in a deliberate controlled manner, thereby precluding an explosion in the enclosure. Other safety features disclosed include an overheat shut-off, pilot light extinguished shut-off and blower malfunction shut-off.

Abstract: An improved power vent and associated control system for a heating apparatus such as a furnace. The invention utilizes a vent blower and a flow control orifice device permitting the use of a single size air moving device and motor with different size furnaces. The control is arranged to discontinue delivery of fuel to the furnace in the event of a blockage of the furnace flue or a failure of the air moving structure. In one form of the invention, a pressure condition is sensed downstream of the air moving structure to detect the failure conditions. In another form of the invention, the control utilizes structure to sense the speed of the air moving device. The invention comprehends the use of a motor for driving the air moving device which varies in speed substantially between the unloaded and loaded conditions. The air moving device preferably unloads under high discharge pressure conditions, such as by a blocked flue.

Abstract: A method and apparatus for maintaining the desired level of excess air in a two stage gas furnace system. Low and high pressure switches are placed across the heat exchanger and are successively closed, as the inducer motor accelerates during purging, when the pressure drop reaches the respective theoretically desired low and high firing pressure drop levels. As the switches are closed, the inducer motor speeds are sensed and recorded, with a ratio of the two then being calculated. After firing, the ratio is then directly applied to a desired high firing motor speed to obtain the desired low firing motor speed.

Abstract: A low intensity infrared radiant heating system comprising an exhaust effluent temperature sensor for disabling burner operations to keep thermal operating efficiences within preselected limits. A minimum burner run timer is used to avoid corrosive condensate accumulation in the primary emitter length. Multiple burner systems utilizing a microprocessor control system is disclosed.

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 heating apparatus comprising a water container, a firebox for heating the water in the water container, a heating chamber containing a plurality heat emitting members disposed therein, a water storage tank disposed on the water container, and a fan for blowing hot air around the plurality of heat emitting member and circulating the heated air into the room whereby the heating apparatus produces hot air with a controlled humidity while at the same time reducing fire danger and pollution due to dust smoke and ash.

Abstract: An ignition control system for a direct ignition gas appliance, such as a furnace. A main gas valve, spark generator, flame sensor, and purge blower are all interconnected to a single controller. The controller issues a purge signal to the blower for a first predetermined period. Thereafter, for a second predetermined period, the controller issues an interconnect signal to allow the main gas valve to open and an ignition signal to cause the ignition source to ignite the gas flowing into the appliance from the valve. If the controller thereafter fails to receive a signal from the flame sensor, the attempt at ignition was unsuccessful. After a predetermined number of unsuccessful attempts at ignition, the controller issues a lockout signal to the valve. Moreover, the controller includes redundant circuits for detecting malfunctions within itself and responsively closing the main gas valve.

Abstract: A furnace is operated such that the air-fuel ratio and the temperature rise are maintained constant so that the efficiency remains constant over the range of operation.

Abstract: A safety device for monitoring the condition of the condensate outlet conduit in a high efficiency furnace is provided which comprises a float member positioned in a condensate trap arranged to float on the condensate and to rise in response to a rising level of condensate in the trap to block the gas vent inlet. A pressure sensing device is utilized to sense the back pressure in the vent and when the float blocks the vent inlet, the back pressure increased and the sensing device will then operate to terminate operation of the furnace.

Abstract: A forced air heater (10) includes a removable burner module (26) in which all of the burner components are mounted on a common support plate (42) to facilitate mounting of the burner module in the heater and removal of the burner module from the heater for servicing. An elongated burner tube (46) has a closed flattened end (50) receivable in a location-and-orienting bracket (76) to locate a single burner orifice (52) in a sidewall of the tube in proper position with respect to a pancake flame-spreader plate (78). A gas valve (44) and ignition device (58) also form part of the burner module 26. A combustion chamber (24) is of essentially box-shaped construction, with one open end (36), and includes an inclined baffle plate (40) which enhances mixing of combustion products and intake air in the chamber. A forced air blower (28) is mounted adjacent a heated air discharge opening (36b) of the combustion chamber (24).

Abstract: A monitor for a gas appliance vent includes a conduit section that is mounted in line with a vent leading from a furnace or other gas appliance. The conduit section has an interior tubular plenum member which extends across the vent interior. The tubular plenum member has upstream facing openings therein. An outer end of the tubular member passes through an aperture in the conduit section. The outer end is open to allow flow therethrough from the upstream facing openings. A switch is mounted in proximity to the outer end. The switch is thermally responsive to respond to the heated flue gases that flow out the outer end. The switch is operably connectable to either an alarm or a fuel line shut off valve.

Abstract: Burner apparatus including fuel burners and a pilot light burner associated with each fuel burner. A solenoid-operated valve controls the supply of fuel to the fuel burners. Thermocouples heated by the pilot light burners energize electromagnetic coils that actuate reed switch units closing a circuit to the solenoid-operated valve. A magnet system actuates the reed switch units to close them during start up.

Abstract: A dual-rate fuel flow control system for the gaseous or liquid fuel supplied to the burner of a space heater, comprising a valve controllable to supply full fuel flow to the burner at the start of a heating cycle to deliver full heat to the heat exchanger chamber in which circulates the heat transfer fluid, and controllable to supply reduced fuel flow to the burner simultaneously with starting the circulating of the heat transfer fluid from the heat exchanger to the space to be heated.

Abstract: A liquid fuel combustion device which includes a fuel tank, a combustion section which includes an inner and an outer flame cylinder and an outer cylinder surrounding the flame cylinders, and a wick having one end in the fuel tank for being immersed in the liquid fuel therein and the other end disposed between the flame cylinders so as to draw fuel to the other end. Structure is also provided for guiding air through the combustion section to provide oxygen to support combustion between the flame cylinders of fuel evaporated from the wick such that the heat produced by the combustion serves to evaporate the fuel from the other end of the wick. Detector elements are provided for respectively detecting the temperature of the exhaust gas from the combustion section and the temperature of the air guided to the combustion section by the guide structure.

Abstract: A dual-rate fuel flow control system for the gaseous or liquid fuel supplied to the burner of a space heater, comprising a valve controllable to supply full fuel flow to the burner at the start of a heating cycle to deliver full heat to the heat exchanger chamber in which circulates the heat transfer fluid, and controllable to supply reduced fuel flow to the burner simultaneously with starting the circulating of the heat transfer fluid from the heat exchanger to the space to be heated.

Abstract: A burner control system for gas fired apparatus of the powered blower vent type wherein a diaphagm valve for controlling the supply of gas to the main burner of the apparatus is operated by a gas bleed line which is subject to pressure regulation by a servo regulator valve. The bleed line is also subject to on-off control by pneumatically operated bleed valve means which are responsive to the subatmospheric fluid pressure produced in the exhaust vent of the apparatus by an exhaust blower to permit opening of the diaphragm valve only when the fluid pressure level within the exhaust vent is sufficiently below atmospheric pressure. The control system preferably includes switching circuit means which are effective to energize the exhaust blower only during the existence of a pilot burner flame adequate to ignite the main burner.

Abstract: A gas burner which consists of a cylindrical duct forming member closed at one end and open at the other end to receive a gas/air mixture under pressure. The member is perforated so that the gas/air mixture flows to the outside of the member where it is burned. The duct is provided with a cone-shaped plug for reducing the volume of the duct from the open end towards the closed end so that a constant velocity of gas/air mixture is maintained within the duct to obtain a uniform static pressure on the outside in the region where the gas/air mixture is burned.

Abstract: Apparatus is disclosed for operating a gas furnace system (100) having an air intake (102) for supplying external air into a sealed chamber (110) for input to a gas burner assembly (118). Exhaust air from within the combustion burning chamber (140) is applied through an exhaust duct (170) directly into an environment (174) which is external to the furnace system (100) but which is still within the environment to be heated. The furnace system (100) also includes a conventional fan limit assembly (142) wherein the typical high limit setting is substantially decreased so that a blower fan (160) is activated at lower than normal temperatures. In addition, the conventional gas furnace burner is replaced with a burner assembly (118) having substantially small burner ports (130).

Abstract: An improved power vent and associated control system for a heating apparatus such as a furnace. The invention utilizes a vent blower and a flow control orifice device permitting the use of a single size air moving device and motor with different size furnaces. The control is arranged to discontinue delivery of fuel to the furnace in the event of a blockage of the furnace flue or a failure of the air moving structure. In one form of the invention, a pressure condition is sensed downstream of the air moving structure to detect the failure conditions. In another form of the invention, the control utilizes structure to sense the speed of the air moving device. The invention comprehends the use of a motor for driving the air moving device which varies in speed substantially between the unloaded and loaded conditions. The air moving device preferably unloads under high discharge pressure conditions, such as by a blocked flue.

Abstract: A warming apparatus uses a gas burner which comprises a burner body and a plurality of tubular flame nozzles projecting radially from the burner body. The tubular nozzles have an internal diametr which ranges from about 1 mm to about 4 mm, and the projecting length of the tubular nozzles which extends from the burner body is within a range of from about 10 mm to about 40 mm. The nozzles have axially directed nozzle openings. The warming apparatus comprises the gas burner in combination with first and second radiators and a heat interception plate positioned between the burner body and the radiators.

Abstract: A gas-fired, forced air furnace system employing a fiber matrix burner element and a condensing-type heat exchanger to achieve both high system thermal efficiency and low emission of NO.sub.X and other gaseous pollutants. The value of excess air in the fuel-air reactants supplied to the ceramic fiber matrix burner is selected to be equal to or greater than ten percent to provide NO.sub.X emissions below fifteen ppm on an air-free basis, with CO and HC emissions substantially comparable to those from existing furnaces, and the surface area of the condensing portion of the heat exchanger system is designed to produce sufficient condensation of moisture in the combustion gasses to produce an overall system thermal efficiency of at least about ninety percent.

Abstract: The present invention relates to a self-checking safety switch control circuit for a power combustion system. The circuit comprises a safety switch, a combustion blower relay, a thermal pilot switch, and a fuel supply system. The safety switch operates to detect flow through the combustion system. The safety switch either operates the pilot switch directly or operates the fuel supply system directly to shut down the system if no flow through the combustion system is detected. The circuit has a self-checking feature because combustion cannot be initiated in a subsequent cycle of the system if the safety switch remains in the proven condition from the previous combustion cycle.

Abstract: A combustion control system having incorporated therein an electronic circuit for driving and controlling a proportional control valve provided on a fuel supply line to control the amount of combustion and thereby maintain the temperature of fluid to be heated by combustion at a constant level even when the amount of the fluid varies per unit time. The output voltage of a bridge circuit including a sensor for detecting the temperature of the fluid as a component is fed to operation amplifiers for differentiating, integrating and proportional amplification to control the control valve with the resulting output. The system is best suited for use in instantaneous water heaters.

Abstract: An apparatus for heating a fluid, as air, having a housing surrounding a heat transfer chamber. A casing having a combustion chamber is located in the heat transfer chamber. A motor driven fan mounted on the housing operates to supply air to the combustion chamber and move air through the heat transfer chamber. Fuel, as waste oil, is metered to the combustion chamber and burned. The air supplied to the combustion chamber moves the burning fuel in a circular pattern to promote combustion of the fuel adjacent the casing thereby heating the casing. The air moved through the heat transfer chamber picks up heat from the hot casing. The heated air is discharged through an open grill into the environment surrounding the apparatus.

Abstract: An improved control system for a pulse combustion apparatus is disclosed. The system includes starter means operable to activate blower means for starting the apparatus. First switch means is provided and is responsive to a first predetermined air velocity in the air intake of the apparatus as representing satisfactory operation of the blower means. The first switch means is coupled to and adapted to activate the gas supply means and ignition means of the apparatus when the first predetermined velocity is achieved. Second switch means is also provided and is responsive to a second predetermined air intake velocity representing establishment of combustion in the combustion chamber and adapted to deactivate the ignition means and blower means while maintaining the gas supply when the second predetermined air intake velocity is achieved.

Abstract: A heating system of the type having a combustion chamber with a fuel burner, an inlet for combustion air and an exhaust stack is improved by adding a variable-speed induced draft blower, a flow-restricting stack orifice and a fuel valve sensitive to the exhaust gas flow rate through the stack orifice. The fuel valve turns on at a first predetermined exhaust gas flow rate and turns off at a second predetermined exhaust gas flow rate, which is lower than the first predetermined rate. The fuel valve also supplies fuel at a rate proportional to the exhaust gas flow rate. Sensing of the differential pressure across the stack orifice is used to determine the exhaust gas flow rate.

Abstract: A gas-fired, forced air furnace system employing a fiber matrix burner element and a condensing-type heat exchanger to achieve both high system thermal efficiency and low emission of NO.sub.X and other gaseous pollutants. The value of excess air in the fuel-air reactants supplied to the ceramic fiber matrix burner is selected to be equal to or greater than ten percent to provide NO.sub.X emissions below fifteen ppm on an air-free basis, with CO and HC emissions substantially comparable to those from existing furnaces, and the surface area of the condensing portion of the heat exchanger system is designed to produce sufficient condensation of moisture in the combustion gasses to produce an overall system thermal efficiency of at least about ninety percent.

Abstract: The disclosure relates to pulse combustion apparatus generally and to air furnaces of the pulse combustion type. In one aspect, the invention provides a furnace which includes a combustion chamber and an exhaust system disposed in a passageway for air to be heated. The exhaust system includes a primary exhaust pipe, a manifold to which the primary exhaust pipe is coupled, and a plurality of heat exchange pipes which extend from the manifold across the air passageway. The primary exhaust pipe, manifold and heat exchange pipes form a reasonant system with the combustion chamber so that the ignition of successive fuel charges in the chamber causes pressure waves to oscillate throughout said exhaust system including the heat exchange pipes for promoting transfer of heat from the pipes to air flowing through the passageway in use.

Abstract: A system for monitoring the operation of a heating apparatus having a combustion chamber with associated air and fuel supplies and an exhaust path includes sensors for monitoring temperatures at the combustion chamber. A microprocessor and a display receives signals from these sensors and has a keypad to permit calculation and display of parameters indicative of proper operation of the heating system including fuel usage per unit time. Limit values can be stored in the processor memory to trigger alarms when temperatures or fuel usage exceed the set limits. Various measured and calculated values can be displayed.

Abstract: A refractory lined firebox is encased in a low profile furnace shell of generally rectangular configuration. Mounted on top of the firebox within the furnace shell is a heat exchanger which provides alternating passageways at right angles to one another through which flue gas and air to be heated flow in heat exchange relationship. The heat exchanger and firebox are so related that the axes of the passageways are inclined from the horizontal and the flow through them is generally upward as well as lateral. The furnace includes special combustion air ducts for use in combustion of the solid fuel. The furnace is also equipped with a back-up liquid fuel burner and a control system which activates and operates the liquid fuel burner in response to total consumption or burn out of the solid fuel in the firebox.

Abstract: An electronically controlled space heater includes a ceramic block heating element fed by a metering pump with fixed volume charges of liquid fuel at a rate dependent on temperature requirements. The heating element is located within a combustion chamber. Exhaust gases vented from the combustion chamber are applied directly to a thermocouple whose voltage output is utilized to vary or maintain the frequency of a pulse circuit driving the metering pump. An operator-adjustable potentiometer functions as a thermostat to establish a desired temperature reference value to which the thermocouple output is continuously compared. Start-up and shutdown circuitry precludes the development of unsafe operating conditions.

Abstract: A forced air furnace includes a conventional fuel fired, primary heat exchanger and a secondary heat exchanger associated with the stack. The secondary exchanger includes a phase change material having a transition temperature within the range of the stack temperature, and which is disposed in heat exchange relation with the flue gases flowing through the stack. The secondary exchanger also includes duct means for conveying the circulated air in heat exchange relation with the phase change material; and the flow path through the secondary exchanger is an alternative path controlled by a damper. When the primary exchanger is turned on, the phase change material in the secondary exchanger is charged from the flue gases of the primary exchanger. When the phase change material is in condition to release stored heat, a temperature responsive control shuts off the primary exchanger and diverts the circulated air through the secondary exchanger.

Abstract: A furnace having a nitrogen-heat separator comprised of a heat absorbing mass, such as cast iron plates, containing passages through which products of combustion can pass and deposit heat into the metal mass to thereafter be extracted and utilized, a baffle for directing products of combustion through the nitrogen-heat separator, a fiberglass cloth heat-retaining curtain for blocking the furnace exit and trapping heat inside the furnace when fuel combustion stops, a fan for extracting the stored heat from the nitrogen-heat separator when combustion stops and circulating it throughout the furnace interior.