Abstract: An apparatus for recovering heat, and a flue gas recovery and/or recirculation and/or induced draft apparatus for boilers. The apparatus for recovering heat may be used in combination with the flue gas recovery and/or recirculation and/or induced draft apparatus for boilers. The flue gas recovery and/or recirculation and/or induced draft apparatus receives combustion gases from the apparatus for recovering heat and recirculates a portion of the combustion gases to a burner of a boiler and transmits the remaining portion of the combustion gases through a flue that communicates with the atmosphere.

Abstract: The inside of the metallurgical container is connected to a fan (105) through an exhaust duct (102). An additional gas is introduced in the intake part of the fan (105) preferably through the duct (102). The additional gas introduction flow is regulated in such manner that the gas pressure in the intake part of the fan (105) is maintained at a fixed value, via an adjusting valve (108) preferably placed in an additional duct (107) connected to the exhaust duct (102). A control system (110) regulates the opening and closing of the adjusting valve (108) in such manner as to maintain the gas pressure in the intake part of the fan (105) constant.

Abstract: A biomass fuel gasification chamber, blast tube, and heat exchange chamber are interconnected horizontally and subjected to negative drawing pressure by a large variable speed chimney fan. An auger with an air lock feeds biomass fuel automatically into the gasification chamber. Fuel is moved across the gasification chamber on a partially serrated sloping grate. Three stages of fuel activity are created: anaerobic heating for pyrolysis, combustion, and incandescent charcoal oxydation for gasification. A variable speed fan, variable flue, and directional air duct and baffles control the stages with underfire air. A programmed auger in an airtight chamber removes ash automatically. In large systems a hydraulic moving wedge floor assists the fuel feeding auger and a moving sloping grate moves the fuel. A fan and long preheating duct with baffles and fins inside the gasification chamber preheat and direct air into a blast tube leading from the gasification chamber.

Abstract: The present invention provides a water heater capable of exhausting flue gases from an interior space of a building to an exterior space and is adapted for installation through an upstanding wall. The water heater has an insulated tank with a water inlet and a water outlet together with a flue pipe opening at one end thereof beneath the tank upon a combustion chamber containing a fuel burner. The other end of the flue pipe opens at the top of the tank upon a flue gas collector and has a flue gas restricter for restricting the outward flow of flue gases from the flue pipe. The collector includes a collector box connected to the top of the water heater above and in alignment with the flue pipe, a blower and a low temperature flue gas exhaust line. The collector box has at least one air inlet for mixing air from the interior space of the building with flue gases exiting the flue pipe to inhibit condensation and reduce the temperature of the flue gases flowing through the exhaust line.

Abstract: A draft inducer having a pair of arcuate semi-scrolls within a cylindrical housing defined by a circular inner end plate and a circular outer end plate vertically spaced by a sidewall. A metal conduit element is connected concentrically to the inner end plate and an electric motor is connected adjacent the outer end plate. A fan blower wheel is disposed in the housing coaxially with the conduit element and is drivingly connected to the motor. The semi-scrolls define curved air passages with twin, oppositely directed outlets for discharging fluid flow outdoors at rates minimally effected by ambient wind conditions.

Abstract: An improved unit (10) which supplies combustion air (A) to a furnace (100) or hot water heater (200) is described. The unit includes a switch (59) which continues the operation of motor (14) and fans (12 and 15) in unit (10) until the hot flue gases (H) are vented and to cool exhaust gas pipe (22) after the furnace and/or hot water heater cease to operate to produce heat.

Abstract: A filter apparatus for use with smokestacks, comprising: a smoke collector mounted opposite and spaced from the chimney outlet to collect the smoke emitted from the chimney. A turbine draws the smoke from the collector and feeds it to a circuit where the smoke is first washed by water jets, then by steam jets then again by water jets and is then filtered in an electrostatic filter. If the gases contain living microorganisms, these are killed in a burner. If the gases are not clean enough, they can be recirculated. If the apparatus fails, the gases are safely discharged by the chimney.

Abstract: Electronic control system for a gas-fired/hot air furnace includes a primary control unit which controls the flow of fuel to the furnace. The furnace has heating and cooling space thermostats and a comfort fan to supply heated or cooled air to the space being monitored by the thermostats and an induced draft blower which supplies combustion air into the furnace for heating. A first switch and associated relay drive selectively energizes the comfort fan for low speed heating operation and a second relay switch and associated relay drive selectively energizes the comfort fan for high speed cooling operation. Actuation of the heating thermostat energizes a third switch and associated relay drive which energizes the induced draft blower. A high temperature thermostat located to sense excessive furnace temperatures is also connected to actuate the third relay to energize the induced draft blower in an excessive temperature condition.

Abstract: Virtually complete bonding of salt-forming agents to solids during the combustion of fossil fuels, waste or the like by adding basic solids, in particular CaCO.sub.3 or MgCO.sub.3, can be achieved by the following process steps:the moisture content of the fossil fuels, the waste or the like is adjusted to 10 to 35% by weight;the basic substances are added to the fossil fuels, the waste or the like in the most uniform distribution possible, the stoichiometric ratio of basic substances to salt-forming agents being less than 5:1;after the basic substances have been added, the fossil fuels, waste or the like remain in an essentially sealed container, so that a state of water vapor saturation is obtained;the mixture is then burnt at a fuel bed temperature below the thermal dissociation temperature of the compounds resulting from the basic substances and the halogens.

Abstract: A water heater having an insulated water tank with a cold water inlet line, a hot water outlet line and a baffled flue pipe extending vertically through the tank is provided. The flue pipe extends from a combustion chamber housing a burner located beneath the tank, to a flue gas collection chamber positioned above the tank. The collection chamber is in fluid communicatioon with a blower and a flue gas exhaust line for conveying the flue gases through the exhaust line to a direct through-the-wall vent. Control apparatus is provided for sensing the temperature of the water in the tank and controlling the amount of fuel supplied to the burner in response thereto. The control apparatus turns on the blower when fuel is being supplied to the burner and turns off the blower when no fuel is being supplied to the burner.

Abstract: A method of providing an air circulation and exhaust control system for an oven (20) includes an oven enclosure (24) having a conveyor (40) mounted therein for transporting food products through the oven. A plurality of ribbon burners (100) are mounted within the oven interior (32) adjacent the path of the conveyor to heat the interior of the oven. Heated gases generated by operation of the ribbon burners are received through inlet plenums (140) under operation of a circulation fan (146) and are discharged through discharge tubes (154) extending adjacent portions of the conveyor (40) remote from the locations of the ribbon burners (100). Exhaust gases are removed from the oven interior through discharge ports (180) by exhaust blower assemblies (184) which are operated to remove exhaust gases from the oven interior at a rate proportional to the flow rate of combustion air and gaseous fuel into the ribbon burners.

Abstract: The system comprises a pyrolysis chamber having a tire carcass inlet port and communicating with at least a duct for supplying combustion air, the pyrolysis chamber further communicating with s steam generator and having a stationary bottom of frustum of cone shaped coaxially communicating with the combustion air duct, rotating arm members being moreover provided, associated with the stationary bottom, adapted to cause waste unburnt material to be discharged from an outlet port formed through the stationary bottom.

Abstract: An auxiliary flue is disclosed to vent contaminants from a regenerative burner furnace during secondary operations so as to avoid damage to the burners from such contaminants.

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: An oven (20) includes an oven enclosure (24) having a conveyor (40) mounted therein for transporting food products through the oven. A plurality of ribbon burners (100) are mounted within the oven interior (32) adjacent the path of the conveyor to heat the interior of the oven. Heated gases generated by operation of the ribbon burners are received through inlet plenums (140) under operation of a circulation fan (146) and are discharged through discharge tubes (154) extending adjacent portions of the conveyor (40) remote from the locations of the ribbon burners (100). Exhaust gases are removed from the oven interior through discharge ports (180) by exhaust blower assemblies (184) which are operated to remove exhaust gases from the oven interior at a rate proportional to the flow rate of combustion air and gaseous fuel into the ribbon burners.

Abstract: An incinerator system utilizes recovered heat from the incineration of wood waste left by harvesting of forests to dry green wood products. An automatic feeder loads waste wood into a furnace which discharges combustion gases through a stack wherein a spiral air flow is induced to separate a portion of the gas carrying cinders and sparks from the axial movement of the remainder of gas. The cinder laden hot gases pass through a precipitation chamber where the cinders are recovered and returned to the furnace. The de-cindered gas is then admitted to a kiln via a modulating damper to dry wood.

Abstract: A boiler air flow controlling apparatus for feeding air in a desired air flow to a boiler by cooperation of a first fan for feeding air to the boiler with a second fan for sucking air from said boiler. The apparatus includes means for varying, when the number of poles of at least one of motors for the two fans is changed over, the opening of a damper located in an air course in order to restrict a variation of the inner pressure of the boiler upon such changing over to a value within an allowable range.

Abstract: A combustor including a combustion chamber having two paths for removing combustion exhaust gases, a valve in one path, and means to provide, when the valve is in a closed position, pressure at a downstream side of the valve higher than the pressure inside the combustion chamber to prevent leakage of combustion gases from the combustion chamber through the valve.

Abstract: A ventilator comprising a rotating plate provided on its lower surface with blades forming a centrifugal turbine surmounting the mouth of a ventilation duct or ducts in whose axis said turbine creates an ascending vortex effect. The aspiration to which the main duct or ducts are subjected is obtained by the rotation of a turbine (4a) comprising a flange (4) and a plurality of blades (10) fastened to lower surface of flange (4). The blades have a trough shape facing away from the direction of rotation of the turbine, the blades having an inner edge that makes an angle of less than 90 degrees with the flange.

Abstract: A power venter for connection to an appliance vent system to provide draft and gas flow and which has components mounted exteriorly of a building wall and components extending through the wall, with the latter components including an inner pipe connectable to a vent pipe of a vent system and an outer pipe surrounding the inner pipe in spaced relation functioning as a heat shield and providing an annular space therebetween. The outside components include a vent hood with a blower housing mounted interiorly thereof and having a blower with an inlet communicating with an outside end of the inner pipe and having a blower outlet to atmosphere. An orifice plate is associated with the blower to separate positive and negative pressure areas and has an orifice opening leading to an eye of the blower, with the blower rotatable about an axis offset from the longitudinal axis of the inner pipe to provide a desired blower diffuser angle.

Abstract: An in-line power venter insertable into a vent pipe and having a housing attachable to the vent pipe. The housing has separate negative and positive pressure chambers provided by a separator plate positioned within the housing and having an opening for flow of gas to a blower wheel in the positive pressure chamber. The separator plate has a pair of generally semicircular, oppositely-extending sections disposed above the housing for insertion into the vent pipe to positively separate negative and positive pressure zones within the vent pipe. A flow-regulating plate for draft control is mounted within the housing and is manually-adjustable externally of the housing for movement toward and away from an opening in the separator plate to control the flow rate through the opening to the central area of the blower wheel.

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: An improved design associated with the fabrication and construction of a chimney stack wherein the liner material utilized as the inner liner of the stack which comes into direct contact with the flue gases being conveyed by the chimney stack to the outside atmosphere comprises erodable material having embedded therein a resistance type electrical or thermal conductivity type alarm system capable of detecting the degree of erosion of the erodable liner of the chimney stack thereby providing the ability to monitor when reconditioning of the inner liner of a chimney stack is required. Additionally, there is also incorporated the utilization of turbine blades positioned within the stream of gas flow within the chimney stack such that the flue gases cause the turbine blades to rotate, said rotation then being converted into the generation of electrical energy for utilization outside of or in accordance with the operation of the chimney stack.

Abstract: An apparatus and method for burning fuel in a combustion chamber having an exhaust port. The invention includes a combustion device having a burner head for burning fuel to produce a volitilization zone of high heat. The burner head is positioned in the combustion chamber directly beneath the exhaust port to assure a substantially vertical flame. The upright flame produces a zone of volatilization that continuously contacts the fuel on the burner to vaporize or volatilize a higher percentage of the fuel than in previous combustion apparatuses.

Abstract: A boiler having a discharge gas duct divided into a plurality of passages, respective passages having reheaters and superheaters therein. Gas flow controllers are provided for adjusting combustion gas flow through the respective passages. Evaporators are provided in the passages which have reheaters therein, the convective evaporators being downstream of the respective reheaters.

Abstract: An auxiliary exhaust system for use with a flue includes a conduit communicating at one end with an opening formed in the flue wall and a blower operable to introduce auxiliary air into the flue through the conduit. The conduit is angled so that the auxiliary air enters the flue with a velocity component extending in the downstream direction of the flow of the products of combustion to aid in venting the combustion unit. A damper located within the conduit operates an on-off switch in a blower control circuit which starts and stops the blower when the damper is opened and closed, respectively. The blower control circuit also includes an automatic combustion control which is responsive to flue temperature to increase the speed of the blower whenever the flue temperature is below a predetermined value and to decrease the blower speed whenever the flue temperature is above a predetermined value. The blower includes an access port which enables a fire extinguishing chemical to be introduced into the flue.

Abstract: An energy recovery system for an incinerator. Hot flue gases from the incinerator are discharged into a vertical stack and the lower end of the stack is connected through an auxiliary conduit to a heat exchanger, such as a steam or hot water boiler. An induced draft fan draws the hot flue gases through the conduit and boiler to generate steam or hot water and a damper is located within the conduit. A fuel burner is connected in the conduit and operates to supply heat to the boiler during periods when the incinerator is not operating. A first flow sensing mechanism is located in the conduit upstream of the boiler, while a second flow sensing mechanism is positioned in the stack downstream of the connection of the stack and the conduit.

Abstract: A new and improved incinerator steam generation system subjecting to combustion debris such as municipal waste, utilizing the heat derived therefrom to produce steam for steam boiler, electrical generating facilities, heating facility for industrial or commercial plants, and so forth. This is provided with a series of boilers and controls, both manually adjustable and also automatic, whereby the possibility of fire dangers are minimized, created temperature ranges of boiler gases are constrained to desirable limits, dump stack facilities are automatically controlled as to particular effectiveness for differing types of operating conditions, and where safety features are incorporated to shut down gas flow through the boiler during periods of boiler-water deficiency, excess steam generation relative to demand, and other conditions. Within the furnace area proper the pressure conditions are predetermined and are controlled during operation for desired efficiency, vapor removal, and materials' combustion.

Abstract: An aspirating device for the ejection of gases or fumes has dynamic primary and static secondary extraction means. The static secondary means has lower and upper elements configured in pseudo-frustoconical forms. The upper and lower elements are rigidly fixed to one another. The dynamic primary means are active or passive dependent on the desired level of flow of the ejected fluid.

Abstract: A new and improved incinerator steam generation system subjecting to combustion debris such as municipal waste, utilizing the heat derived therefrom to produce steam for steam boiler, electrical generating facilities, heating facility for industrial or commercial plants, and so forth. This is provided with a series of boilers and controls, both manually adjustable and also automatic, whereby the possibility of fire dangers are minimized, created temperature ranges of boiler gases are constrained to desirable limits, dump stack facilities are automatically controlled as to particular effectiveness for differing types of operating conditions, and where safety features are incorporated to shut down gas flow through the boiler during periods of boiler-water deficiency, excess steam generation relative to demand, and other conditions. Within the furnace area proper the pressure conditions are predetermined and are controlled during operation for desired efficiency, vapor removal, and materials' combustion.

Abstract: A firebox has a liquid or gaseous burner and also a solid fuel grate assembly associated with a solid fuel inlet above the grate assembly for dropping solid fuel particles thereon. The grate assembly includes upper and lower bar type members and an intermediate member of expanded metal. A blower is mounted under the grate assembly and in combination with the latter provides an even pressurized draft for burning solid fuel particles. A sweeping bar on side runs is capable of sweeping clinkers and ashes from the grate assembly. A bottom auger receives the clinkers and ashes and carries them out of the firebox. A forced air inlet directs a flow of air down on the solid fuel inlet to prevent combustion gases from traveling reversely through the solid fuel inlet. A heat exchange chamber includes a plurality of reversely turned tubes arranged in a plurality of paths and connected by end housings capable of removal for inspection and cleaning.

Abstract: Fluid flow in parallel-connected conduits is regulated by sensing the pressures and/or temperatures at the junctions of the conduits, and regulating the supply of power to a fluid propelling means operable in one of the conduits in accordance with a signal which is representative of the sensed pressure drop and/or temperature drop between the junctions. In a furnace installation having an air preheater (14) in a duct (12) and a parallel-connected by-pass duct (18), the pressure difference and/or temperature difference between the junctions (19, 20) of the ducts (12, 18) is/are employed to generate a signal which regulates the supply of power to an induced draft fan (17) in the air preheater duct (12). The damper (21) normally provided in the by-pass duct (18) may be removed or set at its open position.

Abstract: A heater without a chimney is installed inside of a residence. An induced draft system is installed outside of the residence. The heater exhaust gases are connected to the induced draft system with an insulated through the wall exhaust pipe which is cooled by mixing cool outside air with the exhaust gases as they are exhausted to the atmosphere.

Abstract: An apparatus is disclosed for use in venting the products of combustion from a power combustion system such as an induced draft furnace. The apparatus includes a housing having three openings and a baffle. One opening in the housing receives the gaseous products of combustion from the power combustion system. A second opening in the housing is connected to a flue pipe which directs the products of combustion from the housing to an outlet vent. The third opening in the housing has a spillage damper or movable panel which can cover the third opening. The panel is pivotally connected to the outside of the housing above the third opening. When the pressure within the housing is less than the surrounding atmospheric pressure the panel is forced closed by this pressure. The panel is forced open and the products of combustion in the housing are vented to the surrounding atmosphere when a pressure greater than the surrounding atmospheric pressure is present within the housing.

Abstract: A flow control device is provided for use with a fan to prevent pressure excursions in a furnace or any other hardware equipment to which the fan is connected. The control device is connected in parallel relation with respect to the fan so that a recirculating flow path is formed between an outlet of the fan and an inlet thereof. This recirculating flow path controls the pressure differential produced by the fan. The control device includes duct work and a controlled element, preferably, a damper. In a furnace system, an induced draft fan is connected in series with a furnace and the controlled device is normally in a closed position in parallel with the induced draft fan. Upon the occurrence of one or more predetermined fault conditions, the controlled device modulates open to provide a circulating path through the induced draft fan and rapidly controls the pressure differential between the inlet and outlet of the fan.

Abstract: A roof-mounted apparatus is disclosed for discharging exhaust gas at a high velocity. The apparatus includes a stack having a tapered annular cross-section for achieving a relatively high discharge velocity for exhaust gas so that the effective height of the stack is equivalent to that of a considerably taller conventional chimney. The tapered annular stack preferably includes an outer wall and a coaxial inner wall which tapers outwardly toward the outer wall from the bottom to the top of the stack. An in-line fan having an annular outlet which communicates with the bottom of the tapered annular stack is preferably included for impelling exhaust gas admitted to the inlet of the fan into the stack.

Abstract: The invention relates to a method of operating a furnace with gas turbine exhaust as preheated combustion air, in which a gas seal is used. The gas seal housing may for example be a J-shaped tubular device depending from the duct through which the exhaust air flows to the burners, and is open at one end to the duct and open at the other end to the atmosphere. The variation permissible of duct pressure atop the seal in order to keep the seal intact is a function of the vertical range of the interface between the gases in the device and the difference in density between the two gases and can be controlled by adjustment of the damper setting. In normal operation the hot exhaust air flows to the furnace burners under the suction controlled by the damper. The seal is disrupted when the flow of exhaust air is reduced, the colder atmospheric air then being admitted and flowing to the burners so that the furnace continues in operation.

Abstract: An open sided firebox is provided including an upwardly tapering upper bonnet portion. The lower end of an upstanding flue pipe opens downwardly into the interior of the bonnet portion and the upper end portion of the flue pipe is open for exhausting flue gases above the roof line of a building in which the firebox is disposed. A multi-walled outer housing encloses the firebox and includes a front wall having an opening therein through which the open side of the firebox opens. The upper portion of the housing tapers upwardly in cross section and encloses the bonnet. An upstanding flue liner is loosely disposed about the flue pipe and includes a lower end opening downwardly into the upper portion of the housing and an upper end sealed about the upper end of the flue pipe.

Abstract: A combination powered flue products exhaust and preheated combustion air supply assembly is provided for use in association with a heating furnace so that flue exhaust products are given a positive exhaust to the outside while a balanced pre-heated combustion air supply is simultaneously and positively pulled inside. A compartmented main housing is provided having flue products exhaust and combustion air compartments. A flue products exhaust fan is provided in the flue products exhaust compartment and a simultaneously activated and driven combustion air intake fan is provided in the combustion air compartment. An outside air intake pipe is connected to the main housing so as to deliver combustion air to the combustion air compartment for delivery to the furnace area upon selective activation of the combustion air intake fan.

Abstract: A scrubber bypass damper comprises a plate pivotally-mounted to a shaft running across the bypass duct transverse to gas flow. The damper plate self-actuates and rotates about the shaft in response to any pressure differential established across it. A scrubber booster fan is disposed in the main flue at a location downstream of the scrubber and upstream of the outlet of the scrubber bypass into the main flue. When the scrubber is in operation, the pressure rise imparted to the flue gas by the scrubber booster fan is adjusted to keep the damper plate disposed transverse to gas flow through the bypass duct thereby preventing gas flow therethrough. When the scrubber is taken out-of-service, the booster fan is shutdown and the damper plate self-actuates, opening in response to pressure forces exerted on it by the induced draft fan, thus preventing over-pressurization of the furnace.

Abstract: The inlet vanes for an induced draft (ID) fan in a power plant boiler are position controlled in accordance with the furnace pressure to limit the potential destructive power developed by the fan. The ID inlet suction temperature is sensed and a control signal is developed as a function of the inlet temperature to limit the opening of the inlet vanes during boiler startup.

Abstract: A gas burner device having a gas supply and a primary air supply and secondary air supply to the burner and a flue gas vent means leading from the burner for venting flue gases to a place of disposal. The device has a power driven fan in the flue gas vent for providing simultaneously a forced flow of flue gases away from the burner flame and of primary and secondary air to the flame, a temperature responsive variable speed control for controlling the power supply to the fan motor and thereby the speed of the fan and the rate of movement of the exhaust gas from the burner and flame and primary and secondary air to the flame in direct proportion to the temperature of the flue gases.

Abstract: A waste heat recovery system and method for recovering heat from exhaust gases flowing through an exhaust stack or flue from a source of heat. The recovery system includes a heat exchanger located within a bypass assembly that includes a pair of conduits connected to the exhaust stack, and a blower for producing a flow of exhaust gases from the exhaust stack through one of the conduits and the heat exchanger and then back to the exhaust stack through the other of the conduits. The method of the present invention includes the moving of at least a portion of the exhaust gases in the exhaust stack through the bypass assembly and returning such portion back to the exhaust stack.

Abstract: An openable rotor chamber structure for a vertical blower which is disposed on a floor provided within the base section of a smokestack or the like to exhaust smoke within a flue and discharge the same up the stack. The rotor chamber structure has a rotor chamber divided into two equal longitudinally extending portions which can be coupled or separated at a transverse dividing plane including the axis of the chamber, the respective parts of the blower being mounted on one of the two casing portions. A support frame is rotatably anchored on the floor by pins and the casing portion on which the parts of the blower are mounted is fixedly secured thereto. A mechanism is provided for moving the other of the two casing portions on which the members of the blower are not mounted in a horizontal direction.

Abstract: A furnace system having a combustion chamber, and heat transfer surfaces, forced and induced draft fans for moving gas through the burner, chamber, and heattransfer surfaces, first controls for maintaining predetermined gas flows and furnace pressure or draft dependent upon the desired normal operating conditions, and second controls responsive to the flow of the gas exterior to the chamber, e.g., at the inlet or outlet of the induced draft fan and, if desired, at the outlet of the forced draft fan, for controlling a damper or dampers in the gas path or the speed of the fans so as to limit the vacuum which can be developed in the chamber by the induced draft fan to a value less than the chamber vacuum withstanding design value. Also, if desired, the second controls at the outlet of the forced draft fan can limit pressure which can be developed in the chamber by the forced draft fan to a value less than the chamber pressure withstanding design value.

Abstract: A water heater having an insulated water tank with a cold water inlet line, a hot water outlet line and a baffled flue pipe extending vertically through the tank is provided. The flue pipe extends from a combustion chamber housing a burner located beneath the tank, to a flue gas collection chamber positioned above the tank. The collection chamber is in fluid communication with a blower and a flue gas exhaust line for conveying the flue gases through the exhaust line to a direct through-the-wall vent. Control apparatus is provided for sensing the temperature of the water in the tank and controlling the amount of fuel supplied to the burner in response thereto. The control apparatus turns on the blower when fuel is being supplied to the burner and turns off the blower when no fuel is being supplied to the burner.