Abstract: A portable hot water heater for larger-scale applications including emergency use, situations involving hazardous materials, and the like. The hot water heater advantageously efficiently and rapidly heats large quantities of water for providing a stream of hot water for immediate use. The hot water heater includes a pump that can draw water from any suitable water source, a power source, a heating assembly that quickly and efficiently heats the water as it flows through the heating assembly. The heating assembly is attached to a shower head or other fixture.

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: The object is to provide a water heater capable of efficiently transmitting radiation heat of a burner to hot water in a hot water storage chamber, and improving thermal efficiency. In water heater, a second restriction part having a shallower depth than a restriction part is partially arranged along a peripheral edge of a lower mirror plate of a hot water storage chamber, a protrusion part protruding in a ring shape toward the center side of the lower mirror plate is arranged between the restriction part and the second restriction part, and a burner is provided so as to position a burner head of the burner to face the protrusion part.

Abstract: A forward combustion type condensing gas water heater is provided including a burner, a primary heat exchanger, a drain pipe for condensation water, a gathering and discharge device for condensation water, a secondary heat exchanger. The gathering and discharge device and the secondary heat exchanger have center lines different from the primary heat exchanger. Flue gas rises through the primary heat exchanger and passes through the secondary heat exchanger in a direction staggered with respect to the falling direction of condensation water. The condensing gas water heater effectively avoids resistance between the condensation water and the flue gas and prevents the condensation water from flowing to the burner, the combustion chamber, and the ignition pin.

Abstract: A fuel-fired water heater has a single pass condensing-type heat exchanger disposed within its water storage tank portion. The heat exchanger includes a primary non-condensing portion defined by a combustion chamber positioned in an upper interior portion of the tank and having a spaced series of vertical tubes depending therefrom. A secondary condensing portion of the heat exchanger is defined by a plenum having a top side connected to the bottom ends of the vertical tubes, and a bottom side from which a downwardly coiled flue tube depends. A fuel burner generates hot combustion gases that are sequentially flowed into the combustion chamber and then downwardly through the balance of the heat exchanger in a single pass.

Abstract: An arrangement structure of heat exchangers in a condensing gas boiler is provided, which includes a casing provided with a combustion chamber therein, and a gas burner provided in the lower portion of the combustion chamber.

Abstract: A gas water heater includes a power burner, a flue tube, an exhaust plenum, and a draft hood. The flue tube includes a portion that describes at least a 360° loop. Products of combustion are forced through the flue tube under the influence of the power burner, and enter the exhaust plenum. In the exhaust plenum, the pressure of the products of combustion drops such that the products of combustion flow into the draft hood substantially entirely under the influence of natural convection. In one embodiment, the power burner fires down into the flue tube through a side wall of the water heater, the loop of the flue tube is near the bottom of the water heater, and the plenum is in the top of the water heater.

Abstract: The water heater includes a burner and a water tank. Combustion products flow upwardly around the tank through a combustion products path where heat transfer to water in the tank occurs, the path being defined between the outer wall of the tank and a surrounding heat exchanger wall. The combustion products pass through outlet at the upper end of wall, and enter the flue which includes a down flow passage and then pass out through discharge outlet. The down flow passage is defined between a flue outer wall and a thermally conductive partition defining the inner wall of the passage. The partition is adjacent a heated zone of the water heater where stored heat of the water heater is available during quiescent or standby periods when the burner is not operating. The partition between the heated zone and the down flow passage provides a heat transfer path so that heat in the heated zone can transfer through the partition to gases in the down flow passage.

Abstract: An instantaneous type fuel-fired water heater has a variable speed blower that discharges combustion air into a fuel burner utilized to heat water flowing through a heat exchanger portion of the water heater. A portion of the air discharged from the blower bypasses the burner and associated heat exchanger, flows around the heat exchanger, and then mixes with flue gases being discharged from the heat exchanger portion into the flue portion of the water heater. In this manner, such flue gases are cooled by the bypassing blower discharge air to an extent permitting the flue portion to be formed from a low cost plastic material instead of a high temperature metal material such as stainless steel.

Abstract: A water heater comprising a tank defining a water chamber, a water inlet and a water outlet communicating with the water chamber, and a combustion tube extending generally vertically through the water chamber and having an upper end. The water heater also comprises a coil surrounding the combustion tube and having inlet and outlet ends, a second tube communicating between the combustion tube and the inlet end of the coil, and an exhaust outlet communicating with the outlet end of the coil. The water heater further comprises a gas burner firing into the upper end of the combustion tube, and at least one expansion volume between the upper end of the combustion tube and the inlet end of the coil for attenuating noise.

Abstract: A condensation heat exchanger adapted to interface with a gas or fuel-oil burner, the condensation heat exchanger including two coaxial tube bundles placed end-to-end, one of which acts as primary exchanger and the other of which acts as secondary exchanger. Each of these bundles include at least one of a tube or of a group of tubes arranged end-to-end, forming a helical coil, in which the wall of the tube(s) is produced from a material that is a good conductor of heat and has a flattened, oval cross section, the major axis of which is perpendicular or approximately perpendicular to the axis of the helix. The width of the gap separating two adjacent turns is constant and smaller than the thickness of the cross section, the bundles being mounted securely inside a gas-impermeable jacket.

Abstract: A fuel-fired water heater has a three-pass condensing type heat exchanger disposed within its tank and having a central vertical first pass flue pipe separated into upper and lower portions by an internal dividing structure. Respectively coupled to the upper and lower first pass flue pipe portions are circumferentially spaced series of vertical second and third pass flue pipes which circumscribe the central flue pipe within the tank. During firing of the water heater, combustion gases from a power burner are sequentially forced downwardly through the upper portion of the first pass flue pipe, upwardly through the second pass flue pipes to an upper plenum external to the tank, and then downwardly through the third pass flue pipes and the lower central pipe portion into a bottom plenum external to the tank for discharge from the water heater.

Abstract: The invention concerns a heat exchanger comprising at least one helically bound bundle of tubes, whereof the thermally conductive wall has a flattened and oval cross-section, whereof the main axis is perpendicular to that (X-X?) of the helix, while the width of the interstice separating two adjacent turns is small and constant, said bundle being fixedly mounted inside a casing (1) fitted with a pipe for evacuating gases generated by a burner (6), means being provided for circulating cold water inside said bundle, said exchanger being further designed so that the hot gases pass radially through the bundle via the interstices of the turns. Said exchanger is characterized in that the casing is made of heat-resistant plastic material and means are provided for ensuring mechanical containment of the beam in the axial direction, and for damping the thrust loads resulting from the fluid internal pressure, preventing their being transmitted to the casing.

Abstract: The invention relates to a heat exchanger comprising a pair of tube bundles (21, 31) through which the fluid to be heated flows, one primary bundle (21) surrounding a cylindrical burner (40) and the other secondary bundle (31) on which the water steam contained in the combustion gas exhausting from the primary bundle is condensed, whereby the tubes forming the bundles have a flattened section and a helicoidal shape, such that the combustion gas flow between the coils, from the inside to the outside for the primary bundle (21) and in the reverse order for the secondary bundle (31), both bundles being arranged inside a same shell (1). Said heat exchanger is characterised in that the axial dimension (l2) of the secondary bundle is substantially smaller than the axial dimension (I1) of the primary bundle, such that an available space for an exhaust trunking (7) is provided at the end of said secondary bundle (31).

Abstract: A fuel-fired commercial water heater has upper and lower communicated tank portions which are separated by a plenum forming a vertically intermediate portion of a dual pass condensing type heat exchanger. A lower portion of the heat exchanger is defined by a series of vertical flue tubes extending through the lower tank and intercommunicating the plenum with a combustion chamber disposed beneath the lower tank and having a fuel burner with a discharge portion communicated therewith. An upper portion of the heat exchanger is defined by a vertical flue pipe, disposed in the upper tank, that extends upwardly from the plenum and then coils downwardly around itself and horizontally exits the upper tank. During firing of water heater the burner flows flue gases sequentially through the lower tank flue tubes, the plenum, and the upper tank coiled flue pipe structure.

Abstract: A fuel-fired heating appliance has multiple premix type fuel burners horizontally disposed in a row in its combustion chamber and operable in a staged manner. The burners are upwardly spaced apart from a rigid fiberboard insulation panel structure extending along the bottom interior side of the combustion chamber. Sandwiched between and contacting the bottom sides of the burners and the top side of the fiberboard panel is a blanket of resilient ceramic fiber insulation material which functions to (1) prevent uncombusted fuel from firing burners from being circulated under non-firing burners, (2) increase the operating temperatures of bottom sides of the burners during firing thereof to lessen thermal stresses in the firing burners, (3) resiliently permit differential thermal expansion of the burners, and (4) reduce harmonic resonance of the burners, and associated operational noise of the appliance, during firing of the burners.

Abstract: A water heater which includes a heat exchanger having a first passage and a second passage connected with the first passage, a gas burner mounted within the first passage, a push blower having an outlet conmected with the gas burner for forcing air into the gas burner, and a water reservoir mounted surrounding the heat exchanger, whereby when the gas burner is turned on, the push blower will be turned on to force air into the gas burner thereby forcing combustion air generated from fire of the gas burner to move along the first passage and meanwhile the pull blower will be turned on to extract the hot air out of the second passage.

Abstract: The present invention relates to a heat exchanging type boiler that includes: a water retaining reservoir 10 in which a predetermined amount of water is charged; and a combustion chamber 33 for emitting heating gas at a high temperature to the water in the water retaining reservoir 10 through a heating gas supply pipe 20 such that the water in the water retaining reservoir 10 is raised to produce steam at a high pressure, the boiler characterized in that a water discharging film 32 disposed between the heating gas supply pipe 20 and the water and having a plurality of fine through holes such that the water in the water retaining reservoir 10 is not leaked to the combustion chamber 33 and at the same time the heating gas emitted to the water by means of the heating gas supply pipe 20 is distributed in substantially small bubble form.

Abstract: A combustion chamber for a gas-fired hot water heater comprises a top wall which is defined by a bottom wall of an inner tank. A flue extends through the inner tank bottom wall. A circumferential skirt is disposed about the combustion chamber. The combustion chamber is supported elevated from a support surface by a bottom pan assembly of a hot water heater housing. A combustion air inlet means leads to the combustion chamber. A floor shield is supported above the bottom wall and spaced below a gas burner assembly. The circumferential skirt and/or the floor shield are coated on at least one surface thereof with refractory paint to reflect radiant heat inwardly in the combustion chamber whereby to maximize heat transferred to the inner tank and to minimize heat loss through the skirt and floor shield.

Abstract: A condensing gas boiler having a corrosion prevention structure of preventing corrosion caused by using heterogeneous metal is provided, which includes a casing provided with a combustion chamber therein; a present heat exchanger arranged in the casing, which includes a first tubular tube made of a copper material having a plurality first thermal pins formed by processing an outer circumferential surface; a latent heat exchanger disposed at a distance from the present heat exchanger, which includes a second tubular tube whose inner portion is made of a copper material and whose outer portion is made of aluminum, having a plurality second thermal pins formed by processing an outer circumferential surface; end plates contacting and engaged with each other while the present heat exchanger and the latent heat exchanger are fixedly arranged in respective rows and installed in the casing; and a plurality of connection tubes which are mutually connected through a connection portion so that water can circulate throug

Abstract: A portable instant water heater. Water is delivered to a base unit of the instant hot water heater by a pump that draws water from a reservoir through a flow control valve. The water flows into a pre-heater that wraps around a base of the burner and that is heated by the burner. Water is heated in a heat exchanger and then exits the base unit through an outlet spout that swings out from the base unit to dispense water and that may be stored and locked into position in a handle for the base unit. The flow control valve may lower the flow of water through the heat exchanger, so the water has more time to absorb heat and to get hotter. The base unit includes a single control knob that turns on the pump and the burner and operates the flow control valve.

Abstract: The invention relates to an equipment to be used in a gas-fired water heater which equipment contains a combustion chamber (2) and a heat exchanger (1). Accordingly the combustion chamber (2) is made of a ceramic material and provided with slots (3) for crossing the heating elements (4) of the heat exchanger (1) through the opposite walls (5,6) of the combustion chamber (2).

Abstract: A small and compact boiler for providing hot water for indoor heating and domestic hot water and method of operation are provided. The boiler includes a three way valve configured to circulate boiler water through a heating circuit when indoor heat is required, and bypass the heating circuit and circulate the boiler water through the heat exchanger to enable production of domestic hot water.

Abstract: A water heater apparatus includes a water conduit having an inlet and an outlet. A primary heat exchanger has a water side defining a portion of the water conduit. A burner is operatively associated with the primary heat exchanger for heating water in the water side of the primary heat exchanger. A variable flow blower provides pre-mixed combustion air and fuel gas to the burner at a controlled blower flow rate within a blower flow rate range. This apparatus allows the heat output of the water heater to be continuously varied within a substantial flow rate range having a turn down ratio of as much as four to one.

Abstract: A portable instant water heater. Water is delivered to a base unit of the instant hot water heater by a pump that draws water from a reservoir through a flow control valve. The water flows into a pre-heater that wraps around a base of the burner and that is heated by the burner. Water is heated in a heat exchanger and then exits the base unit through an outlet spout that swings out from the base unit to dispense water and that may be stored and locked into position in a handle for the base unit. The flow control valve may lower the flow of water through the heat exchanger, so the water has more time to absorb heat and to get hotter. The base unit includes a single control knob that turns on the pump and the burner and operates the flow control valve.

Abstract: An indirect fired process heater apparatus and method. The apparatus includes a toroidal shell having an outer cylinder and an inner cylinder forming a fluid tight enclosure. A plurality of helical heat transfer coils have transfer fluid passing therethrough wherein said heat transfer coils form an axial passageway. A burner directs heat into the axial passageway. The toroidal shell is in fluid communication with the heat transfer coils in order to circulate the heat transfer fluid therethrough. A plurality of helical process heating coils pass through the toroidal shell in order to heat process fluid passing through the process heating coils.

Abstract: A hot gas water heater has a housing, and at least a pair of concentric coils in the housing through which liquid to be heated is sequentially passed. Each coil has a helical tube with adjacent turns connected by a web member such that the tube and web member form an imperforate coil wall. Hot gas passes sequentially between the coils in co-current flow with liquid flow in one adjacent coil and counter-current flow with liquid flow in another adjacent coil.

Abstract: A condensing gas boiler, which recollects condensed latent heat by uptrend combustion, is provided. Latent heat exchangers are disposed in the same area as that of a combustion chamber, and perpendicular with the combustion chamber. An exhaust gas guiding member is installed so that the exhaust gas is collected into a place in the rear portion of a latent heat portion to then pass through the latent heat exchangers. The latent heat exchangers are installed slantly in such a manner that re-absorption of the condensed latent heat can be done in the latent heat exchangers under the optimal condition. Thus, the condensing gas boiler, which recollects condensed latent heat by uptrend combustion, can realize a product of a high efficiency, lightness and compactness.

Abstract: A steam generator of water-tubes type for burn fossil fuel where instead of the convective heat transfer of the present day boilers, the water-tubes are heated by means of the mechanism of heat conduction in solids. The water-tubes are embedded in a large piece of a metal or alloy of high thermal conductivity, to which the thermal energy of the combustion gas is transferred from a long horizontal tunnel. Besides, in contradistinction with the present boilers, the water-tubes are straight and of high thermal conductivity.

Abstract: A burner apparatus includes a mounting head having a fuel inlet opening defined in the mounting head for receiving combustion air and fuel gas through the opening. An inner support structure is attached to the mounting head. The inner support structure defines an interior zone communicated with the fuel inlet opening of the head. An exterior layer of flexible woven heat resistant material is received about the inner support structure and defines an exterior flame attachment surface. The mounting head may include a radial opening defined therethrough. An igniter is located outside of the mounting head adjacent the radial opening so that the igniter is proximally spaced from a combustion zone surround the burner apparatus. The burner apparatus may include a plurality of foraminous back pressure plates located in the interior zone distal of the igniter for balancing the pressure of the fuel gas/combustion air mixture along the length of the burner.

Abstract: A combination domestic hot water and space heating system has an instantaneous domestic hot water heat exchanger and a low mass boiler-type heat generator connected in a series by a boiler water flow circuit containing a circulating pump. The boiler-type heat generator has an internal reservoir containing between 10 and 20 U.S. gallons (37.85 to 75 liters) of boiler water, which is sufficient to enable the heat exchanger to supply normal short term demand, yet avoid excessive downtime thermal losses. A three-way diverter valve in the flow circuit diverts boiler water to a second heat exchanger in an air handler unit for space heating. Priority is given to domestic water heating.

Abstract: There is provided a water heater unit realizing antifreezing of a water tube and the like of a heat exchanger without providing a backwind stopper on an exhaust tube. The water heater unit comprises a heat exchanger for heating water by a combustion heat of combustion means, water temperature sensors for detecting the temperatures of the water tube connected to the heat exchanger and an air supply fan for supplying air to a combustion chamber in which the combustion means is installed. When temperatures detected by the temperature sensors reach a temperature at which freezing of the heat exchanger is expected, the air supply fan is driven to supply air to the combustion chamber and the air is exhausted toward an exhaust port, thereby effecting heat exchange and antifreezing of the water tube.

Abstract: There is provided a water heater unit realizing antifreezing of a water tube and the like of a heat exchanger without providing a backwind stopper on an exhaust tube. The water heater unit comprises a heat exchanger for heating water by a combustion heat of combustion means, water temperature sensors for detecting the temperatures of the water tube connected to the heat exchanger and an air supply fan for supplying air to a combustion chamber in which the combustion means is installed. When temperatures detected by the temperature sensors reach a temperature at which freezing of the heat exchanger is expected, the air supply fan is driven to supply air to the combustion chamber and the air is exhausted toward an exhaust port, thereby effecting heat exchange and antifreezing of the water tube.

Abstract: An improved flue pipe construction particularly adapted for a fuel fired water heater is disclosed which serves to reduce or minimize heat loss when the water heater is in a standby mode. The flue pipe construction comprises inner and outer concentric flue pipes which define an air space therebetween and one or more valve arrangements associated therewith to selectively restrict air flow through such air space. The valve arrangements include a thermally responsive actuator operative to open and close the valve member in response to heat generated by firing of the burner assembly without the need for any external power supply or interlocks.

Abstract: In a water heater, an outer casing includes a hollow flue tube that extends vertically from an inner periphery of a bottom wall thereof, and an outer surrounding wall that extends uprightly from an outer periphery of the bottom wall and that cooperates with the flue tube to confine a receiving space. A heat-conducting unit is mounted inside the receiving space so as to configure the receiving space with isolated first and second chambers. The first chamber is filled with a thermal superconductor material. The second chamber is adapted for holding water therein. The heat-conducting unit includes a plurality of interconnected upright tubular members that cooperate with the outer casing to confine the first chamber therein. The second chamber is disposed externally of the tubular members. A heat-generating source is mounted below the outer casing for heating the water inside the second chamber.

Abstract: A domestic gas storage water heater utilizes a plastic non pressure tank to deliver mains pressure hot water. The heater may be external or internal of the tank and has a heat out put of about 4-10 Mega joules per hour. A pressure transfer module uses the mains pressure of the incoming cold water to deliver hot water from the tank at mains pressure. The tank may be of larger storage capacity than conventional gas heaters and the arrangement ensures that the heated water in the tank is stratified into layers of different temperature. This enables an uninterrupted supply of hot water to be achieved.

Abstract: The present device relates to a combustion boiler having a fan part provided with a driving motor, a suction fan secured on a rotary shaft of the driving motor and disposed on a suction line, for forcedly sucking air in the room or from the outside, and an exhaust fan secured on the rotary shaft of the driving motor and disposed on an exhaust line, for forcedly exhausting an exhaust gas to the outside. Hence, the air in the room or from the outside is forcedly sucked to the suction line by means of the suction fan and the exhaust gas is forcedly exhausted to the exhaust line by means of the exhaust fan. In this way, the flowing of air is constantly kept in all of the suction, combustion and exhaust lines.

Abstract: A steam generator of water-tubes type for burn fossil fuel where instead of the convective heat transfer of the present day boilers, the water-tubes are heated by means of the mechanism of heat conduction in solids. The water-tubes are embedded in a large piece of a metal or alloy of high thermal conductivity, to which the thermal energy of the combustion gas is transferred from a long horizontal tunnel. Besides, in contradistinction with the present boilers, the water-tubes are straight and of high thermal conductivity.

Abstract: The invention relates to a water heater comprised of a cylindrical tank 18 which has a central flue 20 that is mounted with the cylinder axis 40 vertical. The water heater further includes a gas burner 22 provided the base of the tank 18, which burns a gaseous fuel so as to discharge heated gases up through the central flue 20 from the base to the top of the tank 18. A housing 12 surrounds the exterior of the tank and is spaced away from the domed top 34 and side walls of the tank 18, to thereby define a generally annular cylindrical space 36 between the radially outer surface of the tank 18 and the radially inner surface of the housing 12. The annular space 36 is in gas flow communication with the upper end of the flue 20 and is provided with a discharge outlet 48 located at or adjacent the lower most end of the tank 18.

Abstract: A combination space and hot water heater is comprised of an inner tank having an outer casing spaced therebout with insulation being interposed between the casing and the inner tank. The inner tank has a glass-lined inner surface and a heater is provided within the inner tank for heating a same volume of water within the inner tank. An anode is provided within the inner tank. A closed water circulating circuit is connected to the inner tank for circulating hot water from the tank through heat exchange means connected in the closed water circulating circuit. Preferably, but not exclusively, the heat exchange devices are radiators.

Abstract: The water heater includes a water tank, a burner below the tank, a casing around the outside surface of the tank and spaced therefrom so as to define a flue path within the casing and along the outside surface of the tank for combustion products. Multiple flow restrictions are located in the flue path and extending inwardly from the casing towards the outside surface of the tank and forming regions of restricted flow area so that the combustion products flowing along the flue path encounter the flow restrictions and are restricted and disturbed in flow pattern. The first flow restriction which is first encountered by the combustion products is located at a position along the height of the tank no lower than one third of the overall height of the tank up from the bottom of the tank whereby the lower portion of the tank over which combustion products are flowing are substantially completely exposed to the hottest and most turbulent combustion gases.

Abstract: A hot water heater having a housing with a top chamber, a bottom chamber and a main tank. A cold water inlet pipe runs into the top chamber and extends into the tank. The cold water inlet pipe coils inward, beginning at circumference of the top chamber before extending into the tank, thus increasing the distance the water has to travel inside the heater. Contrastly, the hot water outlet pipe runs straight from the main tank through the top chamber and exits therefrom. The bottom chamber has a dome shaped ceiling with peaked apertures. A burner is positioned along the bottom surface and produces a flame that sends heated air upward, through the peaked apertures into connected heat distribution tubes which travel vertically through the tank. These tubes are angled along their length and have cylindrical fins attached. Once the heat from the flame rises through the apertures, it continues upward through the tubes, until it is released into the top chamber and exits trough an exhaust chimney.

Abstract: A water heater includes a water tank, a combustion chamber below the tank and communicating with the flue tube, and a flue system. The flue system includes a flue tube, and V-shaped fins that are metallurgically bonded to the flue tube wall to divide the flue tube into four flue chambers extending substantially parallel to the longitudinal axis of the flue tube. The V-shaped fins include radially extending apertures that reduce the thermal expansion of the V-shaped fins with respect to the flue tube to reduce stress at the joint between the fins and the flue tube. The flue system also includes a removable baffle hanging in each flue chamber. The baffles include adjustable turbulation surfaces to control the quality of combustion in the water heater.

Abstract: A potable water temperature management system includes a device that produces waste heat and that has a primary purpose other than heating potable water. The waste heat from the device is used to heat potable water in a tank. A heat shedding system is activated when the temperature of the potable water in the tank exceeds a selected maximum temperature. An auxiliary energy transfer system may be activated to heat the potable water in the tank when the potable water in the tank falls below a selected minimum temperature. A controller may be used to monitor the temperature of the potable water in the tank and activate either the heat shedding system or the auxiliary energy transfer system based on the potable water temperature.

Abstract: A water heater includes a tank 10 arranged inside a casing 20 with a burner 16 below the tank so that a heat exchange zone 15 surrounding the tank receives the combustion products. The tank 10 is supported on three edge contact projections 26 resting on ledges 27 located a substantial distance up the sides of the tank. The casing 20 narrows in the upwards direction and a heat shield 30 is coaxially located in the lower portion of the casing where the hottest gases are. A downwardly extending flue 49 outside the casing provides a heat trap. The burner 15 has a burner ring 60 with a unique arrangement of burner ports 62 and a secondary air guide 80. The thermostat probe 14 for the gas valve 17 passes through the heat exchange zone 15 to be intentionally affected by the heat and reduce the achieved operating temperature differential.