US3662738A

US3662738A - Compact forced warm air furnace

Info

Publication number: US3662738A
Application number: US49732A
Authority: US
Inventors: James L Solka; Charles A Reichelderfer; John J Dieckmann; Anthony M Castello
Original assignee: Dunham Bush Inc
Current assignee: Dunham Bush Inc
Priority date: 1970-06-25
Filing date: 1970-06-25
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: GB1310740A

Abstract

A furnace for a forced warm air heating system capable of multipoise installation, including an outer jacket, an inner jacket, a heat exchanger within the inner jacket enclosing a combustion zone, and a burner assembly producing combustion within the heat exchanger. A supply air blower is arranged within the outer jacket to propel return air along a return path beside the inner jacket through the space between the inner and outer jackets and circulate the air within the inner jacket along a supply path in counterflow relation to the return air path. A combustion air blower may be driven from the same shaft as the supply air blower to provide air for the burner assembly.

Description

United States Patent Solka et a1. [45] May 16, 1972 [54] COMPACT FORCED WARM AIR 3,481,321 12/1969 Reichelderfer ..126/116 x FURNACE [72] Inventors James L Solka Bridgewater Charles A FOREIGN PATENTS OR APPLICATIONS Reiche'derter, Harrisonburg; John J. 1,196,671 5/1959 France 126 I0 AA Dieckmann, l-larrisonburg; Anthony M. c n Harrisonburg, a of Primary Examiner-Charles J. Myhre Attorney--Mason, Fenwick & Lawrence [73] Ass1gnee: Dunham-Bush, lnc., Harrisonburg, Va.

22 Filed: June 25, 1970 [571 ABSTRACT 21 APPL 49 732 A furnace for a forced warm air heating system capable of multipoise installation, including an outer jacket, an inner jacket, a heat exchanger within the inner jacket enclosing a [52] US. Cl ..126/1l0 R comb'ustion zone and a burner assembly producing [51] Int. Cl ..F24h 3/02 bustion within the heat exchanger A Supp, air blower i an [58] Field 0 Search 10, B, 116, ranged within the Outer j k to p p l return i along a 126/ l 16 A return path beside the inner jacket through the space between [56] References Cited the inner and outer jackets and circulate the air within the inner jacket along a supply path in counterflow relation to the UNITED STATES PATENTS return air path. A combustion air blower may be driven from the same shaft as the supply air blower to provide air forth 2,658,503 11 1953 Sch'eurer..... ..126/110 bumerassembly 2,089,407 8/1937 Norris ..l26/l10 2,263,098 11/1941 Mueller ..126/110 6 Claims, 4 Drawing Figures PATENTEBMY 16 I972 3.662. 738

SHEET 1 BF 3 JoHNJ'. DECKMANN ANTHoNYMCAs-rc-LLo m J ATTORNEYS PATENTEunmewrz 3.662.738

SHEET 2 OF 3 INVENTORS JAMES L.SOL.KA, CHARLES A-EEKZHELSERFEQ, Joan J-DECKMANN vii/ANTHONY M-CAs-rE LLO Was fw i'wdxQJ Wee ATTORNEYS PATENTEDMAHSIQn SHEET 3 [1F 3 S s R Y m R m m E m V F m a 0 M AE L A K0 L LLNE omuwem QWKAMHALKS aEcM. m M DY a?" m 0 v QNH J AH YM Ho CIA W The present invention relates in general to forced warm air furnace systems, and more particularly to a compact high velocity forced warm air furnace having relatively restricted combustion space, especially designed for use with a high velocity system including a larger diameter plenum pipe and relatively small diameter flexible air ducts with an unencumbered outlet and close coupled attenuator such as disclosed in co-pending application Ser. No. 866,052, now U.S. Pat. No. 3,575,234 filed Aug. 22, l969'by John J. Dieckmann, one of the joint inventors named in the present application.

Design of compact furnaces which will provide efficient heating, particularly for combustion of natural gas, wherein the furnace is of low cost construction, compact configuration,-and is simple and easy to install, making it especially suitable for use in modular homes or factory built home construction, has been recognized as a desirable and needed objective. However, furnace construction heretofore has been relatively larger in size or overall dimension and oftentimes complex and not particularly suitable for such installations or adaptable to the easily installed high velocity small duct system and require different models for different positions.

An object of the present invention is the provision of a novel forced warm air furnace construction, particularly for use in high velocity air conditioning systems, which will be compact and of low cost and relatively simple construction, and wherein the design of the furnace and all controls are such that the same unit, without modification ondesign changes, can be used inmultipoise configurationsmhat is the furnace can be installed as an upflow, a counterflow, or a horizontal unit.

Another object of the present invention is the provision of a compact forced warm air furnace which includes an integral compartment providing the necessary cavity for optionally sliding in a cooling coil assembly when desired to provide both a heating and cooling system.

Another object of the-present invention is the provision of a compact forced Warm air furnace, particularly for use in high velocity heating systems, wherein the furnace provides an integral return air duct or drop by bringing return air over the outside of an enclosed heat exchanger compartment, the return to the furnacebeing-on top of the unit adjacent to the discharge or supply connection.

Another object of the present invention is theprovision of novel compact forced warm air furnace 'wherein the burner is readily adaptable for providing sealed combustion, wherein the combustion air for the burner may be brought in through a separate blower which provides for connecting to a completely ducted system from the outside of the room in which the furnace is installed, commonly outside air.

Another object of the present invention is the provision of a novel compact forced warm air furnace wherein the burner and blower components are designed to be usedwith a compact heat exchanger such as the type disclosed in U.S. Pat. No. 3,481,321 granted to Charles A. Reichelderfer, one of the joint inventors of the present application, providing a furnace characterized by extreme compactness and highly efficient combustion characteristics.

Another object of the present invention is the provision of a compact formed warm air furnace wherein, by nature of the return air system provided, the furnace has a .built in filter system so that no external filter rack or filter grille isrequired.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a fragmentary perspective view, illustrating a furnace constructed in accordance with the present invention and fragmentary portions of the return air drop and the supply duct components to be assembled therewith;

FIG. 2 is a perspective view of the furnace, with portions of the side walls broken away, illustrating the internal components thereof and the circulation of air through the interior of the furnace housing;

FIG. 3 is a fragmentary perspective view, to enlarged scale, with portions broken away, illustrating the supply air blower, the combustionair blower, the burner assembly and the heat exchanger, with arrows indicating combustion air circulation and supply air circulation therethrough; and

FIG. 4 is a vertical section view through the blowers and the motor therefor, taken along the line 4-v-4 of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT While the forcedwarm air furnace of the presentinvention is suitable for operation in any direction of air flow, upward, downward-or horizontal, forpurposes of convenience of illustration and to describe its operation in the most simple manner, the following description is directed to an embodiment wherein the air flow is vertically upward.

Referring to the drawings, wherein like reference characters designate corresponding parts throughout'the several figures, the furnace, generally indicated by the reference character 10, forms a hot air generator and employs an essentially airtight outer jacket or wrapper l l enclosing three sides of the generator 10, having

side panels

12 and 13, rear panel 14, top panel 15 and bottom panel 16. The front or fourth side of the enclosure isprovided with upper and lower front panel sections 17Aand 17B, and a readily dismountable, louvered access panel 17C in the vertical midregion thereof. Within the outer jacket 11, a horizontal partition 18 extends from approximately the lower edge of the removable access panels 17C to.the midregion of the jacket, to underlap the horizontal surface portion of the corner recess or rabbit 19 of an inner jacket or enclosure casing 20 which forms an enclosure for a heat exchanger unit 21. The enclosure defined by the casing 20 is of inverted L-shaped configuration, providing an upper lateral extension 20A projecting forwardly to the front panel 17A of the jacket. The inner casing 20 additionally includes a lower front wall section"20B, which may be spaced rearwardly slightly from a vertical mounting plate 22 on ,which the burner assembly 23, to be later described, is supported,.and includes a rear wall 20C spaced inwardly from the rear panel '14 ofthe outer jacket, and side walls 20D and 20Erespectively spaced inwardly from the

side panels

12 and 13 of the jacket 11. The bottom of the depending leg portion of the intermediate casing 20 defined by the walls 20D through 20E is also closed by delivered to the jacket 11 through a return air duct or drop 25,

shown here of rectangular cross-section near the furnace,

. which is sealed to a rectangular return air. opening 26 inthe toppanel 15 so that the return air is delivered downwardly through the outer jacket or wrapper 11 to the lower region thereof by being returned over the outside of theinner jacket or enclosure casing20 enclosing the heat exchanger compartment. The heat exchanger 21 is preferably of the construction disclosed in said earlier U.S. Pat. No. 3,481,321 granted Dec.

passagesZlA extending vertically therethrough open at the bottom and the top and bounded'by corrugated walls as disclosed in said earlier patent. The air passages 21A are located in one of the leg portions of the generally U-shaped configuration defined by the middle air passage 21A (the one to the left of the passage 21A. as viewed in FIG. 2) while the other leg to the near or right hand side of the passage 21A as viewed in FIG. 2 communicates with the burner assembly 23.

As the inner jacket 20 forming the enclosure for the heat exchanger compartment is spaced inwardly from the walls of the outer jacket or wrapper 11, the return air descending through the return air duct 25 and opening 26 is conveyed downwardly through the outer return compartment defined in the space between the jackets 1 l and 20 to the lower chamber 27 of the furnace below the partition 18 and the bottom 20F of the inner jacket 20. This serves the dual purpose of providing a film of air near room temperature adjacent to the walls of the outer jacket 11, making it possible to design for zero clearances without the need for insulation at additional cost, and also gives good acoustical attenuation to minimize the transmission of noise and thus enhance the acoustical characteristics of the unit without significantly increasing the size of the unit.

Mounted on the underside of the horizontal partition 18 and within the lower chamber 27 is a supply air blower 28, comprising a conventional blower scroll 29 having its discharge outlet portion 29A communicating with an opening 29B in the wall of the comer recess or rabbit 19 of the inner jacket 20 for passage of the supply air streams generated by the rotary impeller 30 of the blower 28 to the space within the inner jacket 20 below the heat exchanger 21 for passage of the supply air upwardly about the outer walls of the heat exchanger 21 and also through the

air passages

21A and 21A thereof. The blower scroll 29 is provided with the usual circular air inlet 29C concentric with the axis of the impeller to draw the return air from the lower chamber 27 into the center region of the blower scroll and discharge the same as supply air through the discharge outlet portion 29A and opening 298 into the inner jacket 20. The impeller 30 is supported on a vertical shaft 31, which is driven by an electric motor 32 supported in depending relation below the scroll 29, as by supporting bracket members or straps 33.

A combustion air blower 34 is mounted on the upper surface of the horizontal partition 18, and is also driven by the same motor 32 to reduce the number of operating units in the system, improve service reliability, and help give a more compact unit. To this end, the impeller 35 of the blower 34 is mounted on an upper portion or extension 31A of the shaft 31 which rises through an opening in the horizontal partition 18, and is located within a blower scroll 36 mounted on the horizontal partition 18, having a circular air inlet 36A in the upper wall portion thereof concentric with the projected axis of the shaft 31 and having an air discharge outlet 36B connected to an air tube or conduit 37 which supplies the pressurized combustion air stream to the burner assembly 23.

The burner 23 may be of conventional construction having an air inlet plenum 23A communicating with the air tube 37 for supplying the combustion air to the burner which receives fuel through a fuel supply conduit 233. The upper burner portion may, for example, be of cylindrical configuration of the construction illustrated in the co-pending patent application Ser. No. 738,920 filed June 21, 1968 by Charles A. Reichelderfer and Frederick L. Runninger.

By virtue of the compact heat exchanger 21 and the power burner 23 supplied with combustion air under pressure, the furnace can utilize a very small diameter venting system, for example a two inch flue exhaust, as indicated at reference character 38, extending from the front wall portion of the heat exchanger to the left of the medial axis or air passage 21A thereof, as viewed in FIG. 2, through the vertical mounting plate 22 and outwardly through one of the walls of the outer jacket 11, for example the side wall 13. The small diameter vent 38 gives reduced stack losses as compared to the usual four or inch vent which would be employed for the same size conventional furnace, and also provides significant cost savings to the installer.

Reviewing the overall air flow patterns through the furnace, the return air descending through the return air duct 25 enters the opening 26 and is diverted laterally and rearwardly as indicated by the arrows 39 to the sides and rear of the inner jacket 20 forming the enclosure for the heat exchanger compartment, providing a film of return air near room temperature inwardly along the side and rear walls of the outer jacket 11. The outer return compartment defined between the walls of the outer jacket 11 and the inner jacket 20 also minimizes direct radiation or transmission of noise from the furnace itself and gives good acoustical attenuation. Further improvement in the acoustical characteristics can be obtained, if desired, by coating the insides of the walls of the jacket 11 with sound deadening material. Also, the disposition of the

blowers

28 and 34 deep inside the unit with no direct communication to outside openings eliminates direct noise transmission.

The return air descending below the bottom of the inner jacket 20 into the lower chamber 27, as indicated by arrows 40, is drawn upwardly through the air inlet 29C of the supply air blower scroll 29 and impelled by the impeller 30 as a supply air stream, indicated by arrows 41, through the discharge outlet portion 29A and opening 298 into the interior of the inner casing 20 to rise about the outer walls of the heat exchanger 21 and through the

air passages

21A, 21A to be heated by thermal exchange with the heat dispensing gas stream within the heat exchanger. The thus heated supply air, indicated by the arrows 42 pass through the upper compartment or cavity within the inner jacket 20 and above the heat exchanger 21 into the supply air duct 24, which may for example be a 7 inch diameter supply duct, which delivers the heated air to a distribution system, such for example as a plenum distribution box 43 and branch air conveying ducts 44 delivering the high velocity conditioned air to terminator devices in the rooms or spaces to be conditioned. The total configuration of the power burner with small diameter vent, compact heat exchanger, low stand by losses, and low casing losses due to return air coming over the outside of the heat exchanger enclosure gives a significantly higher overall efiiciency compared to conventional systems. A heat transfer combustion efficiency of about percent in actual operation is obtainable, compared to about 75 percent for conventional gas fired heating systems. With such a design, the compact heat exchanger and burner assembly can be made out of stainless steel, which is prohibitively costly in the larger less compact conventional designs. It will be appreciated by those skilled in the art that the use of stainless steel for these components would give longer life and eliminate corrosion problems and future field replacement.

The design provides a compartment or cavity above the heat exchanger and within the enclosure defined by the inner jacket 20, which may optionally accomodate a cooling coil assembly when it is desired to provide both a heating and cooling system served by the conditioned air generator 10.

The combustion air supply for the burner assembly 23 may be either drawn from the environment in which the furnace is installed by drawing air through the louvered access panel 17C and the inlet 36A of the combustion air blower scroll 36, or the inlet of the blower scroll 36 can be connected through an optional separate air duct to air originating outside of the room in which the furnace is installed, commonly outside air, for providing sealed combustion. For example, combustion air for the burner may be brought in through a completely ducted system from outside of the furnace room, for example a ducted system which receives outside air and delivers it to the inlet of the combustion air blower 34. There are advantages for such sealed combustion in the modular home and the mobile home industries, and where local codes dictate that combustion air should not be brought from the environment in which the furnace is installed.

The design of the present furnace also reduces to a minimum the time required to install the furnace, because of the simple supply and return connections, which are made at the top of the unit in the upflow position. Conventional upflow furnace configurations typically have a long return air drop to the bottom of the unit that must be provided adjacent to the furnace, whereas the length of the air drop is greatly reduced by the present furnace design.

The present furnace is characterized by a very low amount of floor space to be consumed for installation, which makes it particularly suitable for modular and mobile home construction where space saving is especially important. Typically, a 60,000 Btu per hour input unit would have about 2% square feet of floor area, while 80 and 100,000 Btu per hour input units would consume about 2.8 square feet of floor space. The depth of the unit is minimized to about 23 inches, and as such it can be put into closets and vestibules that are common to the mobile home industry.

It will be apparent that while the foregoing description has been directed to a gas fired unit, the basic design can be employed for oil fired or electrical power heating systems, and the furnaces with this basicdesign may be employed in low velocity more conventional types of heating systems as well as to high velocity air heating systems.

What is claimed is:

l. A furnace for a forced warm air heating system comprising an outer casing having first and second ends perpendicular to an axis and sides paralleling said axis defining a first enclosure, said first end having an air return opening therein, an inner jacket defining a second enclosure having end and side panels spaced inwardly from said ends and sides providing a return air inlet chamber and a second chamber adjacent said first and second ends, respectively, and side enveloping passages therebetween for conveying return air along first flow paths paralleling said axis from said inlet chamber to said second chamber, a heat exchanger located within said jacket having heat exchange walls forming an enclosure about a combustion zone, a burner assembly for producing combustion of fuel and air mixture in the combustion zone, a supply air duct communicating through said first end with the adjacent end panel of said inner jacket for conveying heated air from the inner jacket to rooms to be heated, a motor driven supply air blower having an inlet communicating with said second air chamber and an outlet communicating with the interior of the inner jacket for impelling return air along said first flow paths to said second chamber and circulating the same within said inner jacket along counterflow paths relative to said first flow paths adjacent said heat exchange walls to heat the air and discharge the heated air through said supply air duct, a combustion air blower having a rotary impeller communicating with air externally of said second chamber and with said burner assembly for supplying combustion air under pressure to the burner assembly, said supply air blower including a rotary impeller in said second chamber supported on a common axis of rotation with the impeller of the combustion air blower, and a single motor connected to both of said impellers for concurrently rotating the latter. I V

2. A furnace as defined in claim 1, wherein said heat exchanger is of generally box-like cubic configuration having outer side walls spaced inwardly from the side panels of said inner jacket for flow of blower discharge air therebetween and having intermediate flue channels therethrough for passage of the blower discharge air through the flue channels in intimate thermal exchange relation with flue-bounding walls generally paralleling said outer side walls.

3. A furnace for a forced warm air heating system comprising an outer casing having a top wall, a bottom and vertical side walls defining a first enclosure, said top wall having an air return opening therein connected to a return duct and having a supply duct extending therethrough, an inner jacket defining a second enclosure having top, bottom and side panels spaced inwardly from the top, bottom and sides of the outer casing and defining a blower chamber below the jacket, the side walls and side panels defining uninterrupted air channels therebetween substantially coextensive with said side panels for downward flow of return air to the blower chamber from said return duct along downward flow paths enveloping three sides of the jacket as a film of return air, a heat exchanger located within said jacket having heat exchange walls forming an enclosure about a combustion zone, a burner assembly for producing combustion of fuel and air mixture in the combustion zone, said supply duct communicating with the top panel of said inner jacket for conveying heated air from the inner jacket to rooms to be heated, a motor driven supply air blower having an inlet opening into said blower chamber to receive air therefrom and a scroll discharge outlet communicating with the interior of the inner jacket for circulating return air along said return flow paths to said blower chamber and propelling the air in upward counterflow paths within the jacket relative to said downward flow paths for passage into thermal exchange relation with said heat exchanger and discharge through said supply duct, a combustion air blower having a rotary impeller communicating with air externally of said blower chamber and with said burner assembly for supplying combustion air under pressure to the burner assembly, said supply air blower including a rotary impeller in said blower chamber supported on a common axis of rotation with the impeller of the combustion air blower, and a single motor connected to both of said impellers for concurrently rotating the latter.

4. A furnace as defined in claim 3 wherein said heat exchanger is of generally box-like cubic configuration having outer side walls spaced inwardly from the side panels of said inner jacket for flow of blower discharge air therebetween and having intermediate flue channels therethrough for passage of the blower discharge air through the flue channels in intimate thermal exchange relation with flue-bounding walls generally paralleling said outer side walls.

5. A furnace for a forced warm air heating system comprising an outer casing having a top wall, a bottom and vertical side walls defining a first enclosure, said top wall having an air return opening therein connected to a return duct and having a supply duct extending therethrough, an inner jacket defining a'second enclosure having top, bottom and side panels spaced inwardly from the top, bottom and sides of the outer casing and defining a blower chamber below the jacket, the side walls and side panels defining uninterrupted air channels therebetween substantially coextensive with said side panels for downward flow of return air to the blower chamber from said return duct along downward flow paths enveloping three sides of the jacket as a film of return air, a heat exchanger located within said jacket having heat exchange walls forming an enclosure about a combustion zone, a burner assembly for producing combustion of fuel and air mixture in the combustion zone, said supply duct communicating with the top panel of said inner jacket for conveying heated air from the inner jacket to rooms to be heated, a motor driven supply air blower having an inlet opening into said blower chamber to receive air therefrom and a scroll discharge outlet communicating with the interior of the inner jacket for circulating return air along said return flow paths to said blower chamber and propelling the air in upward counterflow paths within the jacket relative to said downward flow paths for passage into thermal exchange relation with said heat exchanger and discharge through said supply duct, wherein said inner jacket is of inverted, substantially L-shaped configuration in side elevation having an upper horizontal leg portion substantially coextensive in length to the fore-and-aft depth of said outer casing and a depending vertical leg portion extending therebelow of a considerably shallower for-and-aft depth disposing the rearmost vertical surfaces thereof in vertical alignment and defining a burner chamber between front wall portions of said vertical leg and outer casing, said heat exchanger being located wholly in said depending vertical leg portion, and said horizontal leg portion providing a cavity for reception of a cooling coil assembly in said upward counterflow paths of air propelled by said blower.

6. A furnace as defined in claim 13, wherein said heat exchanger is of generally box-like cubic configuration having outer side walls spaced inwardly from the side panels of said inner jacket for flow of blower discharge air therebetween and having intermediate flue channels therethrough for passage of the blower discharge air through the flue channels in intimate thermal exchange relation with flue-bounding walls generally paralleling said outer side walls.

Claims

1. A furnace for a forced warm air heating system comprising an outer casing having first and second ends perpendicular to an axis and sides paralleling said axis defining a first enclosure, said first end having an air return opening therein, an inner jacket defining a second enclosure having end and side panels spaced inwardly from said ends and sides providing a return air inlet chamber and a second chamber adjacent said first and second ends, respectively, and side enveloping passages therebEtween for conveying return air along first flow paths paralleling said axis from said inlet chamber to said second chamber, a heat exchanger located within said jacket having heat exchange walls forming an enclosure about a combustion zone, a burner assembly for producing combustion of fuel and air mixture in the combustion zone, a supply air duct communicating through said first end with the adjacent end panel of said inner jacket for conveying heated air from the inner jacket to rooms to be heated, a motor driven supply air blower having an inlet communicating with said second air chamber and an outlet communicating with the interior of the inner jacket for impelling return air along said first flow paths to said second chamber and circulating the same within said inner jacket along counterflow paths relative to said first flow paths adjacent said heat exchange walls to heat the air and discharge the heated air through said supply air duct, a combustion air blower having a rotary impeller communicating with air externally of said second chamber and with said burner assembly for supplying combustion air under pressure to the burner assembly, said supply air blower including a rotary impeller in said second chamber supported on a common axis of rotation with the impeller of the combustion air blower, and a single motor connected to both of said impellers for concurrently rotating the latter.

5. A furnace for a forced warm air heating system comprising an outer casing having a top wall, a bottom and vertical side walls defining a first enclosure, said top wall having an air return opening therein connected to a return duct and having a supply duct extending therethrough, an inner jacket defining a second enclosure having top, bottom and side panels spaced inwardly from the top, bottom and sides of the outer casing and defining a blower chamber below the jacket, the side walls and side panels defining uninterrupted air channels therebetween substantially coextensive with said side panels for downward flow of return air to the blower chamber from said return duct along downward flow paths enveloping three sides of the jacket as a film of return air, a heat exchanger located within said jacket having heat exchange walls forming an enclosure about a combustion zone, a burner assembly for producing combustion of fuel and air mixture in the combustion zone, said supply duct communicating with the top panel of said inner jacket for conveying heated air from the inner jacket to rooms to be heated, a motor driven supply air blower having an inlet opening into said blower chamber to receive air therefrom and a scroll discharge outlet communicating with the interior of the inner jacket for circulating return air along said return flow paths to said blower chamber and propelling the air in upward counterflow paths within the jacket relative to said downward flow paths for passage into thermal exchange relation with said heat exchanger and discharge through said supply duct, wherein said inner jacket is of inverted, substantially L-shaped configuration in side elevation having an upper horizontal leg portion substantially coextensive in length to the fore-and-aft depth of said outer casing and a depending vertical leg portion extending therebelow of a considerably shallower for-and-aft depth disposing the rearmost vertical surfaces thereof in vertical alignment and defining a burner chamber between front wall portions of said vertical leg and outer casing, said heat exchanger being located wholly in said depending vertical leg portion, and said horizontal leg portion providing a cavity for reception of a cooling coil assembly in said upward counterflow paths of air propelled by said blower.