Gas fired hot air furnace

Oct. 1, 1957

Filed May 9, 1956

R. C. JAYE ET AL

GAS FIRED HOT AIR FURNACE

2,808,047

Sheets-Sheet 1

<img file="US2808047A_D0001.tif" />

Oct 1, 1957

Filed May 9, 1956

R. C. JAYE ET AL 2,808,047

GAS FIRED HOT AIR FURNACE 5 Sheets-Sheet 2

<img file="US2808047A_D0002.tif" />

chard C. Jay a Jehu T. Hwtz

R. C. JAYE ET AL

GAS FIRED HOT AIR FURNACE

Oct. 1, 1957

Filed May 9, 1956

2,808,047

Sheets-Sheet 3

<img file="US2808047A_D0003.tif" />

Oct. 1, 1957

2,808,047

R. C. JAYE ET AL

GAS FIRED HOT AIR FURNACE

Filed May 9, 1956

Sheets-Sheet 4

<img file="US2808047A_D0004.tif" />

Oct. 1, 1957

2,808,047

R. C. JAYE ET AL

GAS FIRED HOT AIR FURNACE

Filed May 9, 1956

Sheets-Sheet 5

<img file="US2808047A_D0005.tif" />

Jahn T. Hintz

<img file="US2808047A_D0006.tif" />

United States Patent Office

2,808,047

Patented Oct. 1, 1957 ώ

2,808,047

GAS FIRED HOT AIR FURNACE

Richard C. Jaye and John F. Hirtz, Watertown, Wis., assignors to Syncromatic Corporation, Watertown, Wis., a corporation of Wisconsin

Application May 9,1956, Serial No. 583,863

Claims. (CI. 126—116)

This application is a continuation-in-part of our copending application entitled Gas Burner, Serial No. 247,716, filed September 21, 1951, now abandoned. As in said copending application this invention relates to gas furnaces and has more particular reference to gas fired hot air furnaces for domestic use.

The primary objects of this invention are to provide a highly efficient low cost gas fired hot air furnace which is exceptionally compact and easy to assemble, which requires a minimum number of screws to secure its component parts together, and which further features burner means of improved design to assure quiet and reliable ignition of the furnace at the dictate of automatic controls.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate two complete examples of the physical embodiments of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a front elevational view of the furnace of this invention, portions thereof being broken away and shown in section;

Figure 2 is a vertical sectional view of the furnace taken through Figure 1 along the plane of the line 2—2;

Figure 3 is a plan view of the furnace shown in Figure 1;

Figure 4 is an enlarged cross-sectional view taken through Figure 2 along the plane of the line 4—4;

Figure 5 is an enlarged fragmentary sectional view taken through Figure 4 on the plane of the line 5—5;

Figure 6 is a cross-sectional view taken through Figure 5 on the plane of the line 6—6;

Figure 7 is a group perspective view of the heating unit, showing one of the combustion chambers of the unit before assembly with the front panel of the unit;

Figure 8 is a fragmentary sectional view at an enlarged scale illustrating the type of snap-in connections employed between the combustion chambers and the front &lt; panel of the heating unit;

Figure 9 is a perspective view of the casing with portions thereof broken away and illustrating the manner in which the heating unit and the flue gas collecting and diverting device are assembled in the furnace casing; and * Figure 10 is a fragmentary cross-sectional view illustrating a slightly modified embodiment of the invention.

Referring now more particularly to the accompanying drawings, in which like numerals designate like parts ,. throughout the several views, the numeral 5 generally designates the casing of a furnace, in this instance shown as having superimposed blower and heating compartments 6 and 7, respectively, with the blower compartment 6 located in the bottom portion of the casing. It will be understood however, that this invention does not 5 depend upon any particular relative arrangement of the blower and heating compartments, for those skilled in the ’ art will recognize that the blower compartment may be disposed in various locations relative to the heating compartment, depending upon installation requirements, as 10 for instance the blower compartment may be entirely to one side or rearwardly of the heating compartment, so as to make possible a reduction in height of the furnace, or it may be located at the top of the furnace, above the heating compartment, to save floor space.

In any event, the furnace casing is comprised of opposite upright side walls 9 and a back wall 10 connected i across the rear edges of the side walls and which, if desired, may be formed integral with them. In the present case, the casing is open at its top and its front, and it is 20 provided with a horizontal shelf 12 fixed to the side and back walls of the casing at an intermediate level in the casing, to divide its interior into the lower blower compartment 6 and the heating compartment 7 thereabove.

As is customary, an inner shell 14 may be secured to 25 the casing to provide inner walls in spaced relation to the side and back walls and cooperating therewith to define a shallow air space in which air may be circulated to prevent the outer walls of the furnace from becoming excessively hot. .

The heating compartment 7 is defined in part by the shelf 12 and by vertical flanges 16 secured to the inner surfaces of the side walls 9 a short distance rearwardly of their front edges 17. These flanges extend continuously from the upper surface of the shelf 12, upon which their °⁵ lower ends rest, to the top of the casing where their upper ends abut the undersides of narrow horizontal ledges 18 turned inwardly from the upper edges of the side walls 9. The inwardly projecting upright flanges 16 lie in a common plane parallel to the back wall 10 of the casing, 40 and as best seen in Figure 4, the inner shell 14 which overlies the side walls of the heating compartment terminates rearwardly of these flanges.

The front of the heating compartment 7 is closed by an upright panel 20 of a height equal to that of the heating 45 compartment and of a width such as to overlie the front surfaces of the outer marginal edge portions of the flanges 16. Elongated vertical strips 21 are secured to the rear of the panel 20 and have continuous finger-like free edge portions 22 overlying the upright marginal edge portions 50 of the panel. Preferably, the outer or free end portions •22 of these strips comprise spring fingers which are resiliently biased toward the rear surfaces of the panel 20, to thus form a slideway therewith in which the inner edge portions of the flanges 16 are tightly received and which 55 constrain the panel to vertical motion relative to the casing so that it must be assembled thereon through the open top of the casing and slid downwardly on the flanges until its lower edge abuts the shelf 12.

It is one of the most important features of this inven60 tion that the heat exchanger 24, which is accommodated in the heating compartment 7, is formed as a sub-assembly with the panel 20 by which the front, of the heating compartment is closed, and that the heat exchanger, so assembled to the panel, is inserted into the heating com⁶⁵ partment through the open top thereof to greatly facilitate the assembly of the furnace. Figure 9 shows the panel 20 and the heat exchanger 24 sub-assembled thereto and partially in place within the heating compartment 7.

The heat exchanger comprises several substantially flat upright combustion chambers 26, the number of such chambers being determined by the heating capacity of the

2,808,047 ranged in the form of a rectangle at a level below the shelf 12 and removal'of the knock-out thus enables an air inlet to the blower compartment to be provided in either side of the casing. Air to be heated may of course 5 be led into the blower compartment by means of a duct 48 having its discharge end fixed in one of the knockout openings, and a filter 49 extending diametrically across the adjacent corner of the blower compartment is employed to clean all· of the air thus entering the blower 10 compartment.

Each of the combustion chambers is provided with a burner unit 51, like that forming the subject matter of our copending application, Serial No. 247,716, filed September 21, 1951. Since the three burner units are iden15 tical, a description of one will suffice for all.

Each burner unit is a casting having a straight , but rearwardly tapering tubular burner section 52, received wholly within the lower portion of its combustion chamber, a straight but forwardly tapering tubular mixing sec20 tion 53 with a mixing chamber 54 at its outer end portion, arid a transversely-enlarged igniter section 55 coaxially joining the rear end of the mixing section with the forward end of the burner section and providing communication between their hollow interiors. The rear 25 erid of the burner section is closed and has supporting feet 57 which project from opposite sides thereof to rest upon indentations 58 in the opposite side walls of the combustion chamber near the rear thereof. At their front ends the burners are supported by a transversely extending 30 manifold 59 extending horizontally in front of the heating compartment arid fixed thereon in any suitable manner, and this manifold and the feet 57 thus cooperate to mount each of the burners in a horizontal position in the lower portion of its combustion chamber.

As best seen in Figures 2 and 4, the mixing section of each burner unit projects a substantial distance forwardly beyond the secondary air inlet opening 32 provided by the mouth of the duct-like extension at the lower end portion of the combustion chamber, so that the mixing 40 chamber 54 of the burner unit is located a substantial distance ahead of tlie'front panel 20 of the heating compartment. The inner end portion of the mixing section 53 of the burner unit extends a substantial distance into the interior of the combustion chamber, and the trans45 versely enlarged intermediate sections 55 of all of the burner units alig'n transversely of the heat exchanger with oval shaped outwardly extending bosses 61 in the sides of the combustion chambers. These bosses have their longest dimensions arranged vertically, and they engage ⁵⁰ with one another, as at 62, -to hold the combustion chambers spaced the desired distances apart so that air to be heated may be circulated upwardly through the heating compartment between the chambers. Each of the bosses is apertured, as' at 63, -to communicate adjacent chambers ⁵⁵ with one another,'arid the abutments of the bosses, al!

around the'holes-63 in them, precludes mixture of gases from the chambers with air to be heated flowing thereacross. These apertured bosses thus cooperate to form duct-like members connecting such adjacent chambers ⁶⁰ laterally with one another, and, as will be brought out at greater length hereinafter, the transversely enlarged intermediate sections 55 of the burner units project laterally into these duct-like portions on the sides of the combus(55 tion chambers to facilitate ignition of all of the burners from a single pilot burner 65, in this case shown mounted on a center burner unit.

The top wall 67 of the burner section is flat and has a fuel discharge portion extending for the full length of the 70 burner section and which preferably consists of a series or row of closely adjacent cross-slots 68 each of which opens to the interior of the burner section. The mixing chamber 54 on the forward or outer end of the mixing section 53, as is customary, forms a venturi, the mouth 75 of which is adapted for connection to an inlet nipple 70 furnace, three being shown in the present instance. These combustion chambers are secured to theHack of the panel 20 and project rearwardly therefrom toward the back wall 10 of the heating compartment, in laterally spaced relation to one another. 'Each of the combustion chambers, as best seen in Figures 3 and 4, is formed of sheet metal and comprises a pair of complementary pan-like sheet'metal stampings 27, having outwardly directed rim portions 28 which abut one another and which are permanently secured together with a welded seam extending continuously therearourid except for short duct-like extensions which project forwardly from the upper and lower portions' of the combustion chamber, as at 29 and 30, respectively.. The lower forwardly projecting ductlike extensions provide inlets through which secondary combustion air may be introduced into the combustion chambers, while the upper'forwardly projecting duct-like extensions 29 provide flue gas ports through which combustion gases 'may he exhausted from each combustion chamber.

It is another highly important feature of this invention that the duct-like extensions 29 and 30 on each of the combustion chambers engage in holes 31 and 32 in the upper and lower portions, respectively, of the panel with a snap-in connection by which the combustion chamber is secured to the panel 20 which closes the front of the heating compartment. Referring to Figure 8, it will be noted' that the marginal edge portion of each of the holes in the upper and lower portions of the panel 20 is bent outwardly at an angle of: approximately 45 degrees, and that the wall of each duct-like extension'has a groove-like deforma’ion extending entirely therearourid to provide a seat 35 which tightly receives the outwardly directed marginal edge portions of the opening in which it fits. It is understood, of course, that the openings, while having the same shape as the cross section'of the duct-like extensions 29 and 30, are slightly undersized, as seen in Figure 8, so that when the duct-like extensions are forced into the openings, from the back of the panel, the .panel flexes slightly and the marginal edge portions of the openings snap into the deformations 34 to securely hold the combustion chambers on the rear of the panel.

While the attachment of the panel 20 to the flanges 16 on the casing, side walls in the manner described serves to tightly hold' the panel ' in place, closing .the front of the heating compartment, and also'provides all of the support necessary for the bank of combustion chambers, of which the heat exchanger is comprised, the heat exchanger may be additionally supported by having the lower rear portion of each combustion chamber rest upon the upstanding flange of an angle ’iron 37 secured to the upper surface of the shelf 12 near the rear wall 10 of the casing and substantially parallel thereto. Also, if desired, the upper'edge of the angle iron may be notched to receive the rim portions 28 on the bottoms of the combustion chambers to thus prevent lateral motion of the rear portions thereof,

With the type of furnace chosen for illustration, the shelf 12 supports'a blower 39, at its underside, the mouth of the blower being received in and fitting a hole '41 in the shelf. Air to be heated is thus blown upwardly into the heating compartment to flow over all of the wall surfaces of the combustion chambers 26 therein, and the heated air. discharges through the open top of the heating compartment, through a short upstanding neck 42 formed on the upper edges of the side and back walls inwardly of the horizontal- ledges -18 thereon. The fourth side of the neck is formed by an-upwardly “projecting flange 42' on the top of the-panel 20. It will be understood that the neck 42 merely provides for the connection of a heating duct 43 to the top of the heating compartment so as to enable the heated air to be distributed to the space of spaces to be heated.

Each side wall 9 of the casing may be provided with knock-out portions 45 defined by perforations 46 ar2,808,047 on the manifold or supply pipe 59. The nipples 70, of course, are equipped with the customary gas jets (not shown) through which the gas enters the mixing section of each burner unit to be commingled with the air drawn into it through the mouth of the mixing chamber. 5 .Heretofore, where the burner unit was not provided with means to assure quick ignition, the velocity of the fuel mixture entering the burner section from the mixing section often was so high that the gas would rush out of the fuel discharge ports which are remote from the pilot 10 flame thus starving those ports nearest the pilot flame and as a result the ignition of the burner was often characterized by a severe flash-back and sometimes a serious explosion.

With the present invention such objectionable conse- 15 quences are avoided through the provision of a special igniter port 72 in the top wall of the hollow transversely enlarged section 55, and a baffle or abrupt constriction 73 at the front end of the burner section, i. e. directly downstream of the igniter port, and in line with the rear trans- 20 verse wall of the igniter section 55.

The presence of this baffle or constriction diverts a portion of the gaseous fuel mixture flowing through the burner unit into the hollow transversely enlarged section 55 and out of the igniter port 72. Thus, as soon as the 25 fuel mixture reaches the burner section it begins to discharge from the igniter port 72 to be ignited by the flame from the pilot burner 65 in juxtaposition thereto.

The baffle or construction 73 also effects a turbulence of the gaseous fuel mixture as it enters the burner section ³⁰to thus assure discharge of such gaseous fuel mixture from that portion of the fuel discharge port, i. e. the row of slots 68, nearest the igniter port; and since the top wall of the section 55 is preferably coplanar with the top wall of the burner section so that the igniter port may ³⁵be close to the fuel discharge port, the fuel issuing from the igniter port and the nearest portion of the fuel discharge port readily commingles. The fuel issuing from the fuel discharge port is, therefore, promptly ignited with the ignition progressing along the length of the ⁴⁰burner section toward the back end thereof as the fuel mixture comes into the burner section.

This arrangement assures rapid and quiet ignition of the fuel issuing from a single burner unit and by virtue of the transverse enlargement of the hollow section 55 and 45 the fact that the igniter port in the top wall thereof extends to the very transverse extremities of this section along the widest portion of the transversely enlarged igniter chamber, the side by side disposition of the several burner units comprising the assembly with their sections 50 55 in close juxtaposition results in a substantially continuous igniter port extending transversely across the entire assembly, through all of the combustion chambers. The gaseous fuel mixture issuing from the igniter ports of adjacent burner units thus commingles to form in effect 55 one continuous fuel jet which may be ignited at any point along the length thereof so that all of the burners can be quickly and easily ignited.

As is well known to those skilled in the art the pilot burner is connected with the source of fuel supply through 60 a supply tube 75, and the individual burner units are supported at their inlet ends by means of the nipples 70, the legs 57 serving to hold the units against rotating about the nipples 70.

The front of the casing is closed by upper and lower 65 doors 77 and 78, respectively, the upper door 77 having a length to extend a short distance beneath the shelf 12 from the extreme top of the casing, and the lower door 78 being of a size to close the front of the blower compartment beneath the shelf. The upper door 77 rests 70 upon the forward edge portions of the narrow horizontal ledges 18 on the casing side walls and, for this purpose, it is provided with a rearwardly bent flange 80 along its upper edge, the opposite end portions of which are received upon the flanges 18. After assembly of the door 75 to the front of the casing, holes may be drilled through the overlapped portions of the flange 80 and the ledges 18 for the reception of sheet metal screws 81 which thereby rigidly connect the upper front portions of the casing sides together through the door. The two screws 81, one at each upper front corner of the casing, plug two other screws to be described later, are all that are required in the assembly of the component parts of the furnace casing.

In order to provide a secure connection between the upper door 77 and the side walls of the casing by which the door further serves to reinforce the casing at the front thereof, the door is provided with continuous flanges 82 bent rearwardly from its upright marginal edge portions, the flanges being received in narrow outwardly opening vertical slits 83 provided by channel-shaped formations 84 formed integrally on the front edges 17 of the casing side walls. The flanges 82 fit snugly in these slits to thus tie the side walls of the casing together at its front and ticking noises which might otherwise result during expansion and contraction of the casing walls are thus precluded.

Near its upper portion, the front door 77 is provided with a series of horizontal vents or louvers 86, and it has a second set of horizontal vents or louvers 87 in its lower portion, the latter providing for the admittance of both primary and secondary combustion air into the space between the front door and the panel 20, ahead of the mouths of the lower duct-like extensions on the combustion chambers and the mixing chambers 54 of the burner units.

The space between the upper door 77 and the upright panel 20 at the front of the heating compartment also accommodates automatic control valves (not shown) which govern the flow of gas to the manifold 59 and, during operation of the furnace, assuming the pilot burner to be lighted, the gas issuing from the burner sections of each burner unit burns in a substantially continuous flame along the length of each burner unit in the lower portion of its combustion chamber. The combustion gases rise to the top of the combustion chambers and issue therefrom through the forwardly projecting ducts 29 at the upper ends of the chambers, into a combination diverter and flue gas collector 89 mounted in the top front portion of the casing, ahead of the panel 20.

The flue gas collecting and diverting device 89 is a box-like structure mounted on the front of the panel 20 in a position covering the mouths of the duct-like extensions 29 on the combustion chambers. It has a bottom wall 90 which slants downwardly and forwardly from a location just beneath the mouths of the flue gas discharge ducts 29 to a point substantially directly behind the lowermost louver of the upper group 86 thereof. This slanting bottom wall 90 also extends nearly across the width of the panel 20. The flue gas collecting and diverting device also has a top wall 92 coextensive in length with the slanting bottom wall 90, at a level just above the ducts 29 on the combustion chambers. A front wall 93 joined to the forward edge of the top wall 92 extends downwardly therefrom close to the rear of the upper door, approximately half-way to the forward edge of the bottom wall 90 so as to leave a generous opening 94 in the front of the unit directly behind the upper louvers 86. A short upstanding flange 96 bent up from the rear edge portions of the top wall extends entirely across the diverter and rests against the front of the panel 20.

The diverter and flue gas collector is also provided with opposite side walls 98 parallel to the opposite sides of the casing and joining the top and bottom walls of the unit, A short vertical duct 99 fixed in a hole in its top wall 92, provides for the discharge of flue gases from the furnace.

Another feature of this invention resides in the fact that the combination flue gas collecting and diverting device is provided with vertical side flanges 100 bent outwardly from the rear edges of its side walls to overlie

2,808,047 flue gas. collecting means into which said flue gas discharge ports in the combustion chambers open; and a plurality of gas burners, one for each of said combustion chambers and mounted in the lower portion thereof, 5 each of said burners comprising an elongated hollow fuel mixing section of substantial length extending rearwardly through the air supply opening in the front of its combustion chamber and having a mixing chamber at its outer end spaced forwardly of the front of the combus10 tion chamber, for connecting the burner with a source of gas and primary combustion air, said fuel mixing section having an outlet at its opposite end located inside its combustion chamber near the duct means which communicates the chambers laterally with one another, an 15 elongated hollow burner section of substantial length located wholly within the lower portion of the combustion chamber and extending rearwardly of said mixing section and having fuel discharge port means opening through its top wall portion along substantially the entire ²⁰ length of the burner section, said burner section being closed at its rear end and having an inlet at its forward end adjacent to said duct means which communicates the chambers laterally with one another, a hollow transversely enlarged intermediate section interposed between ²⁵ and joining said adjacent ends of the burner and mixing sections and located in alignment with said duct means by which the chambers are communicated laterally with one another, said intermediate section providing communication between the interiors of the burner and mix³⁰ ing sections and having spaced upstream and downstream walls projecting abruptly transversely for a substantial distance from the burner unit and into said duct means so that the outer ends of the intermediate sections of burners in adjacent combustion chambers are contiguous ^3u with one another, said intermediate sections having horizontal top walls flush with those of the burner sections and their greatest transverse dimensions being along said top walls thereof, the hollow interior of said transverse intermediate sections defining igniter chambers having ⁴⁰ igniter ports opening through said top walls thereof and extending across substantially the entire transverse dimensions of the latter at a location closely adjacent to the nearest portions of the fuel discharge port means in the burner sections, said igniter ports extending substantially 45 continuously across the plurality of burner units to assure quick ignition of all of the units from a pilot flame located to ignite fuel issuing from the igniter port of any one of the igniter units, and a baffle inside each burner, forming a continuation of the downstream wall of its 50 igniter chamber, for restricting the flow of gaseous fuel mixture into the burner section of the unit so as to assure that a portion of the gaseous fuel mixture initially entering the interior of the igniter chamber will issue from said igniter port therein for ignition before the remainder 55 of the mixture begins to discharge in quantity from the portions of the fuel discharge port means of the burner section remote from said igniter port.

2. In a gas fired hot air furnace: a casing having upright side and back walls; means cooperating with the 60 casing side and back walls to provide an upright heating compartment in the casing which opens through the top of the casing, said means comprising a panel providing the front wall of the heating compartment and extending across the casing substantially parallel to its back wall 65 but at a location spaced rearwardly from the front of the casing; means mounting the panel on the casing in a position closing the front of the heating compartment, said means comprising interengaging male and female elements on the upright marginal edges of the panel and 70 the adjacent sides of the casing which prevent horizontal movement of the panel relative to the casing but provide for vertically guided sliding motion of the panel through the top of the casing during assembly of the panel into the casing; a heat exchanger in said heating compartment, 75 of a size to readily pass through the open top of the the opposite marginal edge portions of the panel 201 A pair of sheet metal screws 101 passing through these flanges and tapped into the panel 20 and the flanges 16 which it overlies, not only mounts the diverting unit in its proper position within the upper front portion of the casing but also serves to rigidly connect the casing sides together through the panel 20 and to preclude vertical motion of the panel with respect to the casing. The screws 101, together with the two employed to fasten the upper door 77 to the top of the casing, are all that are used in the assembly of the entire furnace casing.

As is apparent, the flue gas collecting and diverting device is essential in any gas fired furnace to prevent back drafts from extinguishing the pilot flame of the furnace. In the event of strong back draft, the slanting bottom wall 90 of the unit directs the draft forwardly out of the front of the furnace through the louvers 86 in the upper portion of the door 77.

It will also be noted that the casing is open at its top, forwardly of the panel 20, for the top wall 92 of the flue gas collecting and diverting unit does not completely close off the space between the side walls, nor does it extend upwardly to the level of the narrow horizontal ledges 18. This arrangement provides a ventilating space at the upper front portion of the casing, which has been found to be desirable.

In the furnace described, the heating unit comprising the panel 20 and the combustion chambers fixed to its rear is insertable through the open top of the heating compartment during assembly of the furnace. In the modified embodiment of the invention disclosed in Figure 10, the heating unit is inscrtable through either the top or the open front of the furnace, of course before the upper door 77 is in place thereon.

As seen in Figure 10, this additional feature is made possible by employing a pair of vertically elongated S-shapcd clips 103 to tightly secure the panel 20 to the flanges 16 on the casing sides. These S-shaped clips have an intermediate or central portion which is flatwise received between the upright marginal edge portions of the panel and the flanges 16, and its outer portions are bent around to overlie the outer surfaces of the panel and the rear surfaces of the flanges. The S-shaped strips, however, arc not installed until the heating unit is in place within the heating compartment, with the panel 20 closely overlying the flanges 16. Thereafter the S-shaped strips may be slid endwise down into interlocking relationship with the overlapped marginal edge portions of the panel and the flanges 16.

The lower door 73 has its upper end portion curled inwardly and downwardly, as at 105, to be supported on a hook-shaped lower edge portion 106 on the upper door 77. It is also provided with side flanges like those on the upper door, which are tightly received in the narrow outwardly opening slits 83 that extend continuously along the entire forward edge portions of the casing side walls.

From the foregoing description taken together with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides an improved and greatly simplified and compact gas furnace which achieves greater efficiencies than have been achieved heretofore.