Abstract: An intermediate housing that is, preferably, developed as a cast part and combines several functions and objectives in itself. The intermediate housing not only houses a driving motor for a combustion air blower and a heating air fan, but the driving motor is also disposed by means of a circumferential support developed in the intermediate housing which, at the same time, serves as a stop during the mounting. By means of an elastic bearing of the driving motor, structure-born noise transmission can be avoided. On one side, a combustion air intake connection piece, a fuel supply pipe receiving opening and an exhaust gas outlet connection piece are integrally formed. For the mounting of the heater at a mounting arrangement, the intermediate housing also has passages for fastening screws that are accessible from the direction of the top side of the heater.

Abstract: A direct-fired make-up furnace comprises a cabinet which houses an air blower. A gas fired burner located in a sloped passage, which is formed by walls of a return air compartment and a by-pass air compartment, radiates heat at an angle relative to the blower. The return air compartment substantially blocks direct radiation of the burner. An exit opening of the by-pass air compartment is located between the burner and the blower.

Abstract: A heater for combustion of carbonaceous fuels comprising a casing which surrounds and contains the fuel immediately prior to and during combustion and a heat exchanger of unique design which is positioned within the casing. The efficiency of the heater may be increased by providing an improved system for supplying pre-heated secondary air for more complete combustion of partially combusted fuel in the general vicinity of and/or within the heat exchanger. The heater may be of the self-feeding type for combustion of solid fuels such as wood and, in this embodiment, preferably the casing is generally cylindrical and the heat exchanger is approximately centrally located within the casing whereby it extends generally along the casing axis and is spaced a substantial distance from the casing wall.

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 heater, especially a fuel-operated vehicle heater, is provided with a cylindrical insert that supports the flame in a combustion pipe delimiting the combustion chamber of the heater. The insert is arranged in such a way that an annular space is formed between the inside wall of the combustion pipe and the outer wall of the insert by the insert being located concentrically in the combustion pipe so as to project into the combustion chamber. This insert permits a concentration of the flame in the combustion chamber in the proximity of the burner of the heater, resulting in a burning under more favorable conditions and in a more complete burning.

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

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

Abstract: An improved vaporized liquid fuel combustion apparatus of the type including a cylindrical combustion chamber, a blower, and end plate located between the combustion chamber and the blower and a heat exchanger for heating air by utilizing thermal energy generated in the combustion chamber is disclosed. The combustion chamber, the blower, the end plate and the heat exchanger are separable components and the blower and the heat exchanger are firmly assembled together by tightening bolts at a single flange connection with the end of the combustion chamber making gastight contact with the peripheral end part of the end plate. The one end part of the combustion chamber, the peripheral end part of the end plate are formed and the one end part of the heat exchanger are formed to mate together.

Abstract: A portable LP gas heater includes a combustion chamber the discharge end of which is open and unobstructed and the inlet end of which is defined by a rear head plate having a central primary air inlet into which projects, to a limited degree, a cylindrical fuel nozzle. The projected extremity of the nozzle which positions within the combustion chamber mounts a transversely disposed baffle which is parallel to and spaced preferably about one inch from the rear head plate. Fuel exits from and about the nozzle immediately adjacent and upstream of the baffle. The baffle has a size which permits it to be introduced to and removed from the combustion chamber by way of the primary air inlet. The rear head is further distinguished by a single group of apertures located adjacent its outer periphery in a substantially ring-like pattern.

Abstract: There is disclosed a heating appliance comprising an enclosed housing, a combustion chamber disposed in said housing, and a heat exchanger unit disposed within the housing upon the combustion chamber and dividing the chamber into a cool air plenum zone and a hot air plenum zone. The heat exchanger comprises a plurality of rows of spaced tubular conduits preferably having spaced heat conducting fins disposed thereon and having inlet ends communicating with the combustion chamber and through which combustion gases pass and outlet ends communicating with an exhaust manifold for conducting effluent combustion gases out of the heating appliance housing. An air intake opening is disposed in the housing adjacent the heat exchanger and the cool air plenum zone to permit movement of air into the cool air plenum zone and into contact with the heat exchangers.

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

Abstract: In an arctic vehicle having a heater for the passenger compartment, it is oposed to add an external heat exchanger to remove (condense) moisture from air flowing through the heater. The relatively dry air discharged from the heater into the passenger compartment is less likely to produce fogging or icing on interior surfaces of the vehicle windows. Eliminating or minimizing the fogging-icing condition improves passenger visibility. The invention has special application to military vehicles.

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: Vehicle heater with a tubular combustion chamber and with a pot-shaped heat exchanger crimped over the combustion chamber leaving an annular space, said heat exchanger deflecting the combustion gases in an axial direction. In order to improve the efficiency of such a vehicle heater and to keep the manufacturing and material costs as low as possible, a coaxial, double-walled pot is provided in such a vehicle heater, leaving an annular space between it and the heat exchanger, said pot having an opening in its bottom area and being connected at that point to the annular space between the combustion chamber and the heat exchanger in such fashion that the combustion gases are guided in the chamber between its inside wall and its outside wall and are from there conducted away by an exhaust pipe.

Abstract: In a combustion type heater for an automotive room heating system including a box-like casing which accommodates a combustor, an air blower for feeding air to the combustor, a fuel pump for feeding fuel to the combustor, a heat exchanger, etc., an outside air inlet port is formed in that portion of at least one side wall of the casing which is adjacent to the fuel pump. Air taken in through the outside air inlet port is caused to flow toward the fuel pump to cool it.

Abstract: A warm air blow-out device for box-shaped stove is disclosed, which comprises a casing having a warm air flow-out path formed in an upper portion of the casing interior and air withdrawal openings formed in a bottom and a front wall lower portion of the casing and a cross flow fan extending horizontally in an upper portion of the casing interior and rotated by a motor. The opposite sides of the bottom of the casing are provided with respective legs, which include permanent magnets which can be held attracted to the top of the stove. Behind the legs, support members are provided to be in contact with the rear wall of the room heater casing for supporting the casing of the device.

Abstract: Vehicle heating unit comprising an air intake connection and an exhaust connection, which connections are communicable with corresponding inlet and outlet ducts through the vehicle bottom. In order to perform, in such a vehicle heater, the disassembly of the heating unit, even after several years of operation and consequently corroded coupling clamps for the exhaust manifold and the air connection pipe, a coupling unit attachable to the vehicle bottom is provided. The coupling unit comprises plug couplings or contact pressure couplings, equipped with gaskets for receiving the connections, and, associated therewith, coupling pipe sections oriented toward the outside. The exhaust manifold and the air intake manifold can be attached in the usual way to these coupling pipe sections. However, these manifolds need no longer be detached for the dismounting of the heating device. The coupling unit can be mounted within or externally of the vehicle.

Abstract: A heater including a generally cylindrical shell defining its housing arranged in a very closely spaced relation to the outer periphery of its combustion chamber assembly and its fan device as it bounds a plenum chamber therebetween. The combustion chamber assembly has its discharge end adjacent the discharge end of the shell. The relative configuration of the outer peripheral surface of the combustion chamber assembly and that of the discharge end portion of the shell creates therebetween a passage through which the fan device, on energization thereof, produces a very high velocity flow of a thin layer of air which, on discharge, is throttled and abruptly and sharply driven into the center of the flow from the assembly. The effect of this is to moderate and influence a relative uniformity of the temperature of the discharge and rapidly project it outwardly of and considerably beyond the heater.

Abstract: A power gas burner of the gun type. The burner embodies an air tube that is mounted on the appliance with which the burner is to be used. Primary and secondary air is supplied to the air tube by a blower of the turbo-compressor type that is driven by a motor through an adjustable speed drive. Fuel gas is supplied to the air tube through an eductor tube. Gas is supplied to the eductor at regulated pressure through a metering orifice. The discharge end of the eductor is open and is located on the axis of the air tube and in the throat of a venturi that is also mounted on the axis of the air tube. Air supplied by the blower flows at high velocity through the throat of the venturi on the exterior of the eductor, resulting in a reduction in pressure in the venturi at the discharge end of the eductor. This primary air is mixed in the venturi with gas discharged from the eductor.

Abstract: A safety apparatus for shutting down a room heating device upon detecting incomplete combustion in the burner of the heating device. A detecting element is arranged to provide an output to a setting circuit. When the output changes due to a change in combustion, the circuit cuts off fuel supply. Additional circuitry is provided to vary the predetermined operation level of the circuit depending on whether a room air circulation fan is operating or not.

Abstract: A fan accessory for recovering heated air generated by a heater in which ambient and heated air are induced to enter inlets into a housing, are blended within the housing, and are directed from the housing into an area to be heated.

Abstract: A fan accessory for recovering heated air generated by a heater in which ambient and heated air are passed through a housing in separate passageways and wherein the ambient air flowing through its passageway provides an aspirating effect on the heated air to increase the flow of heated air through its passageway and out of the housing and to facilitate blending of the ambient and heated air outside the housing.

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: A heating system in which the rpm of the combustion air blower can be selectively decreased by an especially simple and economical arrangement and is achieved by selectively connecting an incandescent plug, utilized for igniting the fuel-mixture only during the starting period, as a series resistor to the electric motor driving the combustion air blower after completion of the starting period. In accordance with a preferred embodiment, connecting of the incandescent plug as a series resistor is produced by way of a relay operated contact and an actuating circuit therefor, a selectively closable switch and a contact of a combustion monitoring thermostat being located in the actuating circuit for controlling activation of the relay operated contact.

Abstract: A temperature responsive blower control attachment for a wood-burning stove. The attachment is mountable to or seatable on a heated external surface of the stove and provides thermostatically regulated operation of an electrically operated blower or fan that circulates air heated by the stove. Temperature is sensed through an element which is in contact with the heated surface of the stove, but the other circuit elements of the attachment are isolated from and are not subjected to the potentially damaging temperature of the stove surface.

Abstract: A portable heater comprising a housing composed of separate parts including a lower part having a bottom and side wall portions defining a trough, components of said heater including a combustion chamber assembly and a support, said support positioning in a sense transverse to said lower part, said combustion chamber assembly and said support having in connection therewith means for seating to and interfitting with means in connection with said side wall portions of said lower part in a drop fit thereof to said lower part, said support mounting thereon a motor and a fan blade assembly for powering said heater and developing therein a pressured flow of air to and about said combustion chamber assembly and means for delivering fuel and igniting the fuel in delivery thereof to the combustion chamber of said assembly, said interfitting means being constructed and arranged to position said combustion chamber assembly and said support and said fan blade assembly in a substantially direct alignment on and within sai

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

Abstract: A portable heating unit comprising a heater and a low velocity blower, an elongated lightweight collapsible flexible heat carrying duct and an intermediate high velocity intake fan unit for mixing the low velocity heated air from said portable heater with ambient air and introducing the mixed air streams into the inlet end of said flexible duct. The intake fan unit includes a venturi for assuring adequate mixing of the air within the elongated flexible collapsible tube to provide a high velocity flow of air at a substantially constant temperature level along the length of the flexible tube. The tube is provided with a plurality of openings arranged in spaced intervals to eject high velocity jets of heated air at locations where they may be used most effectively.The unit is designed to be positioned upon the ground and the remote end is sealed and preferably staked or otherwise held to the ground to prevent undue movement.

Abstract: An improved heat arrester boot interposed between sections of a smoke pipe or like conduit means for extracting heat from waste gases and smoke. The heat arrester boot includes an inner core which can be easily removed for the purposes of cleaning when coated with creosote and the like while the remainder of the heat arrester boot remains in place.

Abstract: An auxiliary heater device comprises a tubular combustion chamber surrounded by a heat exchanger 50 as to define a gap therebetween. The peripheral wall of the combustion chamber is provided with a plurality of circumferential projections that extend into the gap in a manner that reduces direct contact heat exchange between the combustion gases flowing through the gap and the peripheral wall by blocking axial flow of the gases along the wall in contact therewith and by deflecting these gases toward the heat exchanger pipe.

Abstract: A maximum efficiency stove or furnace for heating homes or other buildings. The stove includes a primary combustion area for burning a primary fuel, such as wood, and secondary combustion areas for burning the gases of combustion after they leave the primary combustion area. The combustion chambers and areas are at least partially surrounded by air heating enclosures through which ambient room air is forced, preferably by a fan, for heating. Air for sustaining combustion is preheated in a preheating chamber and fed through separate intakes to both the primary and secondary combustion areas. A single draft control is provided to control air flow through the preheating chamber and to simultaneously control the flow of preheated air to and through both said primary and secondary combustion air intakes.

Abstract: An energy storage and distributing device having a heat storage chamber arranged for retaining heat which can be received from a solar collector arrangement or from a furnace or furnaces disposed within the chamber itself. Mounted on the chamber is a plenum arrangement disposed for directing warm fluid to a space to be heated, such as a room or rooms of a house, while a fluid distribution system is associated with the plenum and the chamber for alternately directing a fluid current directly into the plenum and directly into the chamber, and thereby supplying the plenum selectively with warm fluid from one of the chamber or from a source disposed outside the chamber. In this manner, solar energy, and the like, can be fed directly to the plenum, or stored in the chamber, or if solar energy is not available for whatever reason, and insufficiient heat energy is present in stored form within the chamber, a furnace or furnaces can be employed to supply the requisite heat energy.

Abstract: A heat exchanger assembly for an undercounter furnace includes first and second complementary, flanged sidewalls shaped to provide a fire chamber. Integral lower combustion air intake and upper exhaust flue are formed from the same sheet metal as the sidewalls. The width of the fire chamber is less than its height and length. A circulating fan is located behind the fire chamber and between the intake and flue ducts, taking room air from the rear of the casing and forcing it forwardly to sweep over both sidewalls and into the room to be heated. The heat exchanger is mounted to a removable chassis.

Abstract: A stove having an external casing provided with an opening and a cylindrical fire chamber disposed within the casing and provided with a hole arranged adjacent to and in communication with the opening of the casing. Arranged extending transversely across the cylindrical fire chamber is a grate, while a door assembly is disposed removably covering the opening provided in the external casing. Included in the door assembly is a hinged cover provided with a vent for controlling draft in the fire chamber, and with a lock which releasably secures the cover to a cowl of the door assembly on which the cover is hingedly mounted.

Abstract: A thermostat controlled window furnace for heating a room features a construction wherein the air required for its operation is comprised on the one hand of outside air used solely for combustion purposes, to service a heat transfer component, and on the other hand of air drawn from the room, to be heated in passage through the heat transfer unit and returned to the room to elevate its temperature. The arrangement provided for inflow of room air insures that it will exhibit the general temperature of the room. The furnace not only provides for an effective separation therein of outside air and room air which is utilized thereby but for a return to the room of heated air in a manner to inhibit a chance or premature intermingling thereof with that portion of the room air being drawn into the furnace the function of which, in part, is to signal the general temperature of the room to a furnace thermostat.

Abstract: Disclosed is a means for heating a space with hot air comprising essentially first and second enclosures, the second enclosure being completely surrounded by and spaced apart from the first enclosure to form an air chamber for the circulation and heating of air. Energy for heating the air is supplied by burning fuel (wood, coal, etc.) disposed on a plurality of spaced apart, grate forming, tubelike members lying in a common plane positioned inside of the second enclosure. A terminal portion of one end of the tubes bridge across the air chamber and the tubes terminal edges are exposed to the space sought to be heated; terminal edges of the other end of the tubes are exposed to and communicate with the air chamber.

Abstract: A wood burning stove for providing heated air to a room or similar area includes a fire chamber, a hearth in the forward portion of the fire chamber, draft inlet means at the front of the fire chamber and a flue at the rear of the fire chamber. Between the hearth and the flue is an enclosed air chamber having front and rear walls; the air chamber communicates at its bottom with the ambient air and at its top with one or more air pipes which extend to the front of the stove and there open to the ambient air. A baffle plate is positioned between and spaced from the air chamber and the flue. Ambient air is heated by passing it through the air chamber and air pipes after they have been heated by hot gases rising from a fire burning on the hearth; the hot gases contact the air pipes and the front wall of the air chamber and, because their normal path of travel to the flue is altered by the baffle plate, contact the rear wall of the air chamber as well.

Abstract: The stove combustion chamber is lined with a layer of refractory material. Above this a baffle extends at an angle upwardly from the rear wall of the stove part way toward its front wall. Three tubular heat exchangers open at their forward ends on a grill on the front of the stove, and extend rearwardly over the combustion chamber and baffle to a duct mounted on the rear of the stove. The refractory material and baffle help retain heat in the stove to keep the heat exchange tubes warm, and a blower, which is connected to the duct and is controlled by a thermostat, blows warm air from inside the tubes outwardly through the grill into the room containing the stove.

Abstract: This invention relates to a skid-mounted portable heater blower unit for use on the surface to supply high temperature hot air to subsurface installations for the purpose of shrinking heat shrinkable sleeves around splices or other repairs made in underground cable, such heater being characterized by a serially-ducted preheater which draws ambient air in from the outside and warms it by passing it through the ducts back and forth four times in heat exchange relation to the hot products of combustion exiting the unit along the outside of an internal combination combustion chamber and final stage heat exchanger. The preheated air from the final pass through the preheater enters the secondary stage heat exchanger and follows a helical path around the outside of the combustion chamber while flowing in concurrent relation to the flame inside thereof and countercurrently to the products of combustion exiting around the outside.

Abstract: The space heater of the invention features an improved motor-transformer package which may be easily applied to and removed from the heater, as an integrated unit. The design and mount of this package makes it extremely easy to service and insures that in the placement and operation thereof the total package will be surrounded with an insulating flow of air, the cooling effect of which guarantees a longer and more useful operating life for the included components and related apparatus. In the preferred embodiment illustrated, the motor and transformer elements of the package are connected, in a superposed relation, to opposite sides of a mounting plate the design of which essentially dictates the required placement of the package in a heater housing.

Abstract: A forced air room heater for installation in a Franklin stove includes a mounting plate configured for covering the flue opening located in the back wall of the stove and having a central opening passing therethrough. A plenum chamber arranged for placement above the baffle which divides the firebox of the stove has an inlet interconnecting it to the opening in the mounting plate and an outlet opening outside of the stove. An electric motor powered fan is attached to the mounting plate opposite the inlet for forcing air first into the plenum where it is heated, then out of the outlet. In one embodiment the outlet opens out of the stove through its front door opening. In a second embodiment the outlet exits the stove through the mounting plate allowing operation of the stove with its door closed.

Abstract: A heat exchanger comprising a combustion chamber adapted to burn fuel having an inlet at one end for fuel and an outlet at the other end for exhaust gases and wherein a sheath surrounds the combustion chamber to form a chamber for heated air, the combustion chamber having a plurality of radial fins projecting into the heated air chamber. One of the ends of the sheath is axially spaced from the end of the combustion chamber having the fuel inlet and the other end of the sheath extends axially beyond the other end of the combustion chamber to an outlet for discharge of heated air. A second sheath surrounds the first sheath and encloses the combustion chamber and defines an annular space with the second sheath open to ambient air which flows through the annular space and then through the air chamber past the fins to the outlet for heated air.

Abstract: A forced air assembly for attachment to an otherwise unjacketed space heater consisting of a fan or blower centrally mounted in a relatively thin (height compared with width) channel, the channel being adapted to wrap around varying contours of stoves by virtue of a series of cut-out regions in side walls of the channel. Air is forced through the channel, heated, and flows out of the ends of the channel.

Abstract: This heating apparatus includes an air flow chamber having outer and inner, generally cylindrical and parallel walls within which a combustion chamber is nested. The combustion chamber includes means for burning a fuel and has outer and inner parallel, generally cylindrical heat conducting walls. It is coupled to an exhaust duct which has at least a portion thereof surrounded by the inner wall of the air flow chamber. In one form air is driven by an electric fan through the air flow chamber around the combustion chamber and out to a distribution duct. The fan also blows air into the combustion chamber for combustion of the fuel. In another form, a fan is driven by th combustion exhaust gases thereby propelling air through the air flow chamber and into the combustion chamber via a compressor wheel. Other forms include heat-conductive members placed into contact with the exhaust duct or with the air chamber to further heat the air before it enters the distribution duct.

Abstract: A liquid fuel burning heater for vehicles in which the burner unit has a housing which is surrounded by a radially spaced casing, and the heat exchanger has spaced inner and outer jackets axially aligned with the housing and casing, so that the air flows between them past the latter into the former. The casing and at least the outer jacket of the heat exchanger are integral parts of a unitary casting; the burner unit may be a self-contained subassembly, pre-assembled in its housing.