US1984933A - Furnace structure - Google Patents

Description

ro. J. KUENHLD 1,984,933

` FRNACE STRUCTURE Dec. 1s, 1934.;

Filed oct. 17, 1951. 5 ysheets-sheet 1 J mvNTon la?, 'a V BY f l f7@ W o. J. KUENHOLD FURNAGE STRUCTURE:

' Dec. 1s, 1934.l

Filed Oct. 17, 1931 5 Sheetsf'Sh'eet 2 AAfonmew Dec.- A18, 1934. K f o. J. KuENHol-.D 1,984,933

FURNACE STRUCTURE Fled'oct. 17,1931 v '5 sheets-sheet s Mv) l iwi v l '/5 d" l "W M fr@ Dec, 18, 1934. o. J. KuENHoLD FURNACE STRUCTURE l Filed ocmw. 1931 5 Sheets-sheet 4 mvENTQR oww DI., o o o o o. boa ,.owomoo *Loowr wwlowowlllowomaoowwwmo .ullwooowdnlwo wowowowolo momomloooowowowwo 7 b l w, I a v f J w A 5 Dec. 18, I1934. o. J. KUENHOLD .1,984,933

FURNACE STRUCTURE Filed OCL- 17, 1931 5 Sheets-Sheet 5 INVENTOR ATTORNEY,

Patented ose; is, 1934 i UNITED STATES FURNACE s'raUc'rUnE ou J. xuenimla, shaker Heights, ohio, u-

signor to The Forest City Foundries Company; Cleveland, Ohio, a corporation of Ohio Application October 17, 1931, Serial No. 569,433

17 Claims.

My invention relates to Aa furnace structure- '5 domestic coal furnace so as to utilize the same air circulating ducts, -registers, etc.

/The objects of my invention are to provide an auxiliary air heating furnace so constructed as to obtain the highest attainable efficiency combined l0' with compactness to fit restricted quarters; to provide a furnace designed for easeand speed of erection; to provideasingle standard construction which may be assembled to suit location relative to the coal furnace, for instance, right or left- .W hand side, and which will adapt itself to practically any domestic warm air heating plant with -least possible special planning or changes to the existing systemito. provide a furnace that will adapt itself witjfcertalnty of successful .opera- 29 tion and no in rference with the operation of the existing system so that the auxiliary furnace and the existing furnace can be used separately or together; and to providean auxiliary furnace embodying the greatest simplicity as to erection and operation.

Various otherobjects and advantageous features of my invention will be seen in the following description and one embodiment thereof may be seen in the accompanying drawings wherein similar characters of reference designate c orresponding parts, and wherein: 1

Fig. 1 is ,a perspective view showing an auxiliary furnace constructed in accordance'with my invention and connected to a furnace of the coal burning'type; Fig. 2 is a perspective view showin g the opposite sides of the auxiliary furnace from those shown in Fig. 1; Fig. 3 is a perspective view of a motor fan unit for creating a forced draft through the auxiliary furnace; Fig. 4 isa transverse vertical section of the auxiliary furnace shown in Fig 1 and 2; Fig. 5 vis a longitudinal vertical sectio through thecenter of the auxiliary furnace; Fig. 6 is a longitudinal vertical section .through the bottom portion of one of the side drums employed in the auxiliary fumace;r Fig. 'l is a horizontal section through the auxiliary furnace and showing the burner structure in plan; Fig. 8 is a front elevation of a part of the auxiliary furnace showing the fire door in` 59 closed position; rig. s is a view similar to Fig. 8 showing the nre door in open position; Fig. 1 0 is a transverse vertical section of'the lower end of one of the side drums; Fig. 11 is a fragmentary perspective view showing the casing panel assembly; Fig, 12.is.a view showing-the front A(Cl. 126-116) support for the side drums; Figs'. l 13 is a plan view, partLv in section, showing the connections between the side drums and the combustion products exhaust, and the rear support for the side drums and middle drum; Fig. 14 is an enlarged sectional view of the burner structure; and Fig. 15 is an enlarged view of the hot :.iir control gate, showing the gate in closed posi- Referring to the drawings. I have shown one embodiment o f my furnace structure designed to be. used in coniunctlon with a coal furnace of the usual type and indicated by A in Fig. 1, as comprising a casing divided into front and back panels 1 and 2 and two side panels 3 and 4, these 15 panels being joined at their meeting edges by interlocking joints as shown in Figs. 4, '1. and 11. To secure the front and back casing panels 1 and 2 in place, the panels are bent reversely andthen'inwardly to form a portion 5 lthat is 20 L-shaped in cross section, see Figs. 7 and 11. This serves, as one of its purposes, to stiften the front and back panels against bending during erection or handling. The side `panels 3 and 4 are provided yon each of. their edges with inwardlyj extending flanges 6 which interilt with the reversely 'bent lz-shaped portion 5 of the front and back panels. Av brace '7 is spot welded to the front and back vertical edges of the front, back and side panels, and when they are nested as shown in Fig. '1, a single bolt or rivet 8 inserted in matched holes at each joint secures the joints to form a substantial structure, the front and back panels being spaced .apart by the inwardly extending flanges of the L-shaped portions 5 on the front and back panels 1 and 2.

vSuitable means are provided for securing the bottom portion of the corner Joints. This means consists of a bottom stiffener angle 9 welded to the front and back casing panels 1 and 2, these stiffeuer angles being-shaped to the bottom of the entire structure and of a size therewith. One. of the" legs on two opposing sides of the stiifener angle is preferably bent upwardly at about a 460 angle priorto assembly, see Fig. 11, whereupon, after the side casing panels 3'l and 4 are propi erly nested with the front and back panels 1v and 2, and alignedand bolted by the bolts 8, these legs 9 may be. bent upwardly to secure the bottom portion ofthe side panels 3\and 4 in proper position relative the front and back panels 1 and 2. Thus, the entire vertical portion of the casing structure may be assembled with the employing of only four .bolts that` are readily accessible, yet a very rigid v structure is provided.` Withthis construction, it will be apparent that the side panels 3 and 4 are interchangeable.

One of the interchangeable side casing panels 3 and 4, in this instance, the panel 3, is provided with an air inlet opening 10 and an air outlet opening 11, the openings being provided with outwardly extending anges 12 and 13 at all edges. A casing top 14 slants upwardly toward the outlet opening 11. The top 14 is provided with upwardly extending iianges ending in hooked shape portions 15 which hook over the top edge of the furnace casing panels as shown in Fig. 4. Thus, a receptacle is formed at the top of the casing which may be filled with sand or other heat retardant and an upper cover 16 is provided for lending the casing structure a neat appearance and, at the same time, add an air space for additional heat insulation. With this construction, the slanting top 12 may be reversed so as to slant upwardly toward the outlet'whether this be on either right or left side as may be required. Each casing panel is provided with an inner lining sheet 1'1 spaced from the panels to provide an air space i'or heat insulation, the air space being open at both top and bottom so as to provide for free circulation between the linings and the outer casing panels. This lining extends upwardly substantially to the level of the lowest portion of the slanting top 12 and is of the same height at the front, back, and sides of the casing with the exception of a cut out portion in one side to receive a hot air gate and control that will be hereinafter described. The interchangeability of the side panels 3 and 4 and reversibility of the top 14 provides an auxiliary 4furnace structure that is well adapted for use on either side of the heating unit of an existing heating system. l Disposed within the casing just described, is a circulating air heating means consisting of a central drum 18 having a burner element 19 therein and two side drums 20 disposed alongside the central drum 18. In this instance, there is one drum 20 on each side of the central drum 18. However, it will be understood that there may be one or more side V`drums on each side \oi.' the central drum, the number being governed by the conditions which the furnace structure i's constructed to meet. The side drums 20 are operatively connected with a central drum by means of tubular connecting ducts 21 which may be of any number desired and the lowermost ends of the side drums 20 connect with a hollow U- shaped vent manifold casting 22 that has its central portion projecting rearwardly through the back casing panel 2 as shown in Figs. 2 and 13 by means of sleeve connections 22. The passages in the vent casting 22 pass diagonally 1 through the casing to the vertical vent duct 23 as shown in Fig. 13. This gives a method of transferring the vent gases from the side drums to the vertical vent pipe having greatest directness and least iiow resistance which is important in securing emcient results. 'Ihis U-shaped manifold casting 22 has an outlet at its top, communicating with the vertical vent passage 23 whichV vents mtoian open draft nood 24 which, in turn, ventsthrough an outlet opening 25 into the chimney by way ot a suitable connecting pipe.

The entire drum assembly is supported by the front and back casing panels 1 and 2, and the side drums 20 are secured to themiddle drum by means of the communicating ducts 21, cross plates 26 at the front of the casing which bolt to the iront casting 28, and rear cross supporting members 27, see Figs. 4. 7, I2 and 13. Such rear cross supporting member 27 is bolted to the vent manifold casting 22 with which the side drums are assembled and through the middle drum and the rear lining plate 29 of such middle Idrum. The rear vent manifold castingA 22 rests on the rear casing panel through which it projects. As to the front casting 28, this is securely bolted to the middle drum before assembly of the furnace, and when the furnace is assembled it is bolted to the front casing panel so as to support the weight of the front end of the entire drum assembly. The above described drum assembly including drums 18 and 20 and the rear vent 'manifold casting 22 may be secured to the end shipped as a unit apart from the casing panel.

The side drums 20, which have sheet metal sides and ends, have the lowermost edges of the sides as well as the front end bent inwardly as shown at 30 in Fig. 10. A bottom casting 31 is provided to receive the sheet metal sides and ends and a series of toggle clamps 32 (see also Fig. '7) hold the sheet metal in engagement with the casting 31. That is, when the nuts-on bolts 33' e tightened the toggle clamps not only pull th sheet metal into firm engagement with the casting 31 but also pushy the sheet metal outwardly and tightly against vertical ianges 34 on the casting 31. As shown the bolt holes in the casting 31 have a vertical extension '35 that is suilciently high to be above any possible water line and thereby 'prevent leakage of water of condensation from the drums at this point. The tops of the middle drum 18 vand the side drums 20 have a similar construction except that the top castings 36 are level across the entire length of the drum. However, the bottom castings 31 are pitched downwardly toward the rearward ends of the drums for drainage purposes, see Fig. 6, the bottom of the U-'shaped vent casting 22 being lower than the bottom castings 31 of the side drums so that moisture will drain into the vent casting and then out of a drainage opening 36' provided therein for such purpose, see

Fig. 13. This opening provides a drain for the entire combustion system.

As hereinbetore stated, the middle drum 18 vis provided with a burner 19 that is preferably a one-piece cored casting having ame jets 37 on the top thereof, thecasting being symmetrical about its vertical transverse, and longitudinal centraliplanes and having supporting lugs 38 at its ends, see Fig. 5. At the rearward end of the burner, the lug 38 tits into a socket 39 in the rear lining casting 29 while, at the front, the lug 38 fits in a socket 40 that takes the form of an inverted U. Thus, to secure the burner in place, the burner is first seated in the rear socket 39 and then the front end of the burner is moved upwardly so that the front burner lug 38 will ilt in the inverted U socket 40. A screw 41 projects through the front 'casting 28 and below `the front burner lug 38, see Fig. 5, to hold the burner securely in place. The lugs 38 are preferably of rectangular cross section so as to prevent rotative movement ot the burner after the lugs are disposed in the sockets, and a mixer 42 is secured to the burner with its outer end ntting within a recess 43, see Fig. 9. in the front casting 28. The above described method of securing the burner in place permits the fuel control valve to be screwed into the end of the mixer and fuel pipe connection to be made directly thereto without other means of support.

To protect the side sheets of the middle drum :gaseosa I8 from excessive heat radiation at points adja' cent the burner element therein, lini'ng plates 44, preferably o f cast iron, are adjacent the burner, see Figs. 4` and '7. To retain the linings in place during shipment and use,- -a sheet messi strip 4s is 'welded ir-riveted to the sides@ of the middle drum whereby'the top endl of this strip may be bent'over the side liningsae in- Fig. 4. This method is employed because it' affords easy replacement 'of 'the side linings incase of their cracking or warping or in case'of internal explosion. With this construction, the

side linings canbulge outwardly without tear-v ing loose from its fastening means or cracking the side lining plates. Likewise, a fi'ontend lining 46 is provided to correspond tothe rear end lining 29 hereinbefore mentioned.

To achieve the desired distribution ir-sir tc all name jets of the burner element 19, thealr openings around the burnerare relatively nar-v row. 'Ihat is, the side combustion chamber'linings 44 have inward extensions 48 that extend' Y passages of the burneris provided with afname;

' an unusual high furnace einciency for 51 which closes the lopening between the pas-'f' .sages except-for very narrow slots 52 o'n 'each side of the baille. By separating 'the Atwo coredlon;H

gitudinal passages of the burner` and the baille 5l in between with a narrow air slot'v on each' side, the airis guided toward the passs in such manner as to prevent the flames of the two longitudinal-parts of the, burner from draw' ing together and merging.'

Provision of these.. restricted air' inlets and the" distribution of air resulting therefrom results ir` the aeration of the flames being more uniform from front to back of the burner in spite of the fact that the air, in the preferred construction, enters the space dsbelow the burner only'at one end. That is, the airentering the combustion' space 54 around and above the burner is di-` verted slightly toward the flames where needed;

but not so much as to cause blowing of the flames and the flames are shorter and snappiex' than they would be otherwise. Needless surplus air is eliminated giving combustion prducts. of higher temperature 'and making possible greater heat transfer. from the amount of heating surface employed, 'and results in the exhaustion o'f the vent combustionproducts at va temperature safely above the'condens'ation point yet with .that combustion products temperature. In order to'have the auxiliary furnace ilt any domestic warml air heating plant; for example, a coal furnace, regardless of whether the coal fur# nace has a cold air intake duct leading1 from the outside or takes its'cold air directly from the basement, the auxiliary furnace .is arranged to receive its cold air supply from-*the base ofthe coal furnace and discharge heated air into the upper part of the coal furnacecsing'as shown' in Fig. 1.

'Io stimulate the air circulation, I provide va motordriven fan including a motor 55 and f an blades 56, of such 'capacity that itwill easily overcome the added resistance to the -air llo'w brought about by transferring the heated air 'tothe coal furnace instead of passing it to the warm air ducts' from the furnace top but not'of great enoughl 'capacity to pull the heated air downwardly within the casing of `.the coal furnace. asiae anditsspeedmaybevariedinproportion .to the warm air exhaust capabilities of the furnace. If this latter eifect Atook place, the entire casing ofthe coalv furnace would become warmed and 'radiate heat into the furnace room. Of course, such heat radiation might at sometimes be desirable. 'In other words, the air delivery capacity of the fan is proportioned so that, aided by the natural draft in the,

auxiliary furnace casing, it will deliver hot air into the. dome of the coal furnace substantially as fast as the warm air pipes leading to the various registers can 'accept' it and no faster. In accomplishing the above circulation, a second essential is also accomplished by withdrawing the cold air from the base of the coal furnace fast enough to prevent the entering cold air from being 'drawn upwardly in the coal furnace casin g, mixing -with the 'heated air in the upper parts of the casing, and impalrins the air circulation through the warm air ducts to the room. With my construction. the circulating -power-of thefanmaybesoadjustedthattheairinthe .motorffan be readily accessible and easily removable.

As shown in Fig. 3, the motor fan is mounted upon a sliding drawer 57 that may be inserted into its desired location through an opening in the c'old air transfer duct 58 provided between the coal furnace and the auxiliary furnace. Strap clamps 59 are provided to hold the motor 55 securely'on the drawer, `a sheet metal Aguard il'protects' the motor from heat radiation by intercepting heat rays and dissipating them by convection, and the motor fan is supported on a flexible member 6l attached to the drawer or slide 57 to absorb vibration of the motor fan.v ,A protecting tube 62 maybe provided for car rylns the current conducting wires 63 to the motor in order to protect them from injury.

On the motor fan drawer being disposed in a provided opening in either the front or back of the cold. air 'duct 56, a vertical panel 64 closes the opening and'vertical flanges 65 on the panel serve to hold the entire assembly in vertical alignment. A handle 66 is provided on the panel 64 for `convenience in withdrawing the motor fan assembly fx'oiri the cold air duet.

Since the cold air duct- 58 may be on either the' rightor left side of the auxiliary furnace depending on whichside of the coal furnace the auxiliary furnace is located andas the motor fan must in either case propel air toward the auxiliary furnace, the motor and fan are so mounted thatV they may be withdrawn from the clamps 59 and be again inserted lwith the fan blades 56 facing in the opposite direction. This reversible feature 'is necessary to adapt the motor ffan unitto the reversibility or-interchange ability-of the side panels 3 and 4 as hereinbe- That is,` the'motor driven fan is of' tendency to pass either up or' inl fore described to adapt the auxiliary furnace to either side of the existing heating unit. It is the airfstream will be properly distributed within the auxiliary furnace.

In order to direct the horizontally incoming air stream, forced into the auxiliary furnace bythe motor fan unit Just described, upwardly and divide it properly into the upward air passages between and around the heating drums 18 and the drum 20, two curved longitudinally disposed air deectors 67 are placed as shown in Fig. 4. These defiectors are secured at the lower end of the middle drum 18 and are provided as a unit with cross members 68 so that when the furnace is assembled the deectors may be placed to face the motor fan unit regardless of whether the latter is to the right or the left side of the existing heating unit. These air defiectors not only deflect the air streams upwardly with Ithe least possible loss of kinetic energy, but spread the air out, prevent backwash of air on either side of the motor fan, and divide the air stream so that relative amounts flow into the various vertical passages proportional to the amount of air heating possible to be done in each passage whereby the air will issue from the vertical passages at substantially an equal temperature.

As a further means for properly dividing the incoming air stream, the middle drum 18 is lower than the side drums, see Fig. 5. In fact, the lowermost end of the middle drum 18 is prefer'- ably on a level with the vertical middle of the air inlet duct 58 whereby it will intercept and divide the incoming air stream with one-half of the air stream passing upwardly on one side of the drum 18 and the other half passing upwardly on the opposite side of the drum. Further, the side drums 20 have their bottom portions above the air intake opening so that no matter on which side the air intake may be located there with be an ample inlet passage and proper division of the air. This feature enables the maximum heating surface to be properly distributed within the available vertical space in the auxiliary furnace.

To control the circulation of air through the auxiliary furnace and into the coal furnace in such manner .that the auxiliary furnace may be Anace to the top of the coal furnace.

segregated from the coal furnace and the coal furnace used alone, a hot air gate 691s provided in the hot air passage 1l from the auxiliary fur- This air gate is pivoted as at 70 with the pivot rod extending outward on each end and a lever 'I1 keyed to one of the extending ends and projecting upwardly in the plane of the gate 69. A tension spring 72, attached to vone end of the lever 71, is anchored to one of the bolts 8 that holds the upper ends of the casing panels together. When the air gate is in its open position, the spring '72 exerts maximum leverage to hold the gate in such position and when the hot air gate isl in its closed postion as shown in Fig. 15, the spring is substantially in alignment with the gate and the spring anchor whereby it exercises insufficient leverage to lift the hot air gate and the gate remains in its closed position. The lever 'il is also used as a hand lever for moving the air gate from closed to open position and vice versa and the 1,9s4,ess

air gate is necessarily reversible, end for end so that it may be adjacent the coal furnace regardless of whether the hot air outlet 11 is on the right or left side of the auxiliary furnace. To effect this, the side anges of the hot air opening are such that the pivot extensions of the air gate may be easily removed therefrom.

As a safety means, a thermostatic means is provided for partly opening the air gate 69 should the air gate be in closed position with the'burner 19 in operation. This takes the form of a thermometal strip '73 that is secured at its lower end and has its free upper end disposed between the outer face of the air gate 69 and the hot air outlet That is, the strip projects upwardly sumciently so that the hot air gate will lie against it when closed, see Fig. 15. .Should the hot air gate be in closed position and the furnace be lighted, the trapped air within the upper end of the casing will heat the thermometal strip 73 and cause it to ben/d' inwardly toward the center of the auxiliary furnace which will push the air gate 69 outwardly sufficiently for the spring 'I2 to exert sumcient force on the lever 71 to completely open the gate. The provision of this' thermostatic gate opening means prevents overheating and possible damage or fire in the event the air gate 69 should be left closed when the auxiliary furnace is placed in operation by lighting the burner 19. Such thermometal strip may be 1ocated` at any point longitudinally of the air gate 69 but is preferably located opposite one of the cross tubes 2l where it will receive maximum heat when the furnace is in operation. However, the location of the thermometal strip is such that heat from the coal furnace does not reach the strip sufficiently to cause it to trip the air gate 69.

'A gas burner valve '14 of the ordinary tapered plug variety, in which a 90 turn of the valve handie '15 moves the valve rotor from full oif to full on position, is provided as a fuel control means.

At the inner end of the plug, an arm 76 is secured and a link 77 connects the end of this arm to a second arm 18 which is keyed to a rock shaft '79.

This rock shaft extends through to the rearward As shown in Fig. 5, the link 8l extends upwardly from the end of the arm 80 and has its upper end connected to a draft control damper 82 located in the vent duct 23 and pivoted at or near its center as at 84. In my construction, another link 85 connects the draft damper 82 to another damper 86 which provides an air control gate to control the volume of air entrained into the vent pipe leading from the collar 25 to a chimney.

With this construction, the draft damper and air control gate operate simultaneously with the burner valve in such manner that when the burner valve is closed the draft damper 82 and air control gate 86 will be in closed position. Reversely, when the burner valve is open, both the draft damper 82 and air control gate 86 will be open as shown in Fig. 5. Likewise, the draft damper and air control gate will assume positions proportional to the degree of movement of the burner valve.

The burner vvalve is of preferably such nature.

fuel begins to issue from the burn'er. This feature assures sulcient damper and air control gate opening when the burner is turned. on only part way and the parts may be so adjusted that the damper and air control gate are opened proportionate to their needs. This is due to the fact that a larger damper opening relative to volume of fuel burned is necessary when the burning is at a low combustion rate because of the slower travel of the combustion products. l

Thus, turning of the rotor of the burner valve 74 automatically controls the combustion products draft openings and hence the volume of combustion products passed into the vent pipe to the chimney is in approximately correct propor` -tion to the amount of gas being burned in the auxiliary furnace. This reduces excess of air in the combustion products passing to the vent pipe and hence prevents a large drop in emciency when the burner valve is. turned on only part way. Likewise, the air gate, by reducing the amount .of opening to suit the immediate needs, reduces the entrained air at the draft hood 24 when' the burner valve is turned on only part way which tends to reduce condensation .in the vent pipe by reducing chilling of the combustion products owing from the auxiliary furnace to below the dew point due to excess air intermixture. When the burner valve is completely turned off, both dampers are simultaneously closed with no attention necessary by the operator which prevents escape of hot combustion products retainedin the drums 18 and 20 so that their contained heat v may be passed into the air which circulates through the auxiliary furnace.

Automatic closure of the air gate 86, when furnace is not in operation, stops inflow of air through the draft hood 24 and into-the vent pipe to the chimney which prevents chilling of the vent system during ofl' periods if the system is under thermostatic control, and, when the auxiliary furnace .is vented into the smoke pipe of the coal furnace as is preferred, prevents checking of the coal furnace draft when the auxiliary furnace is not being4 used. Thus, the draft for the coal furnace is not impaired when the coal furnace is used alone., The' fact that the draft f position. This is an added safety feature.

'The air gate 86, shown in its extreme open position in Fig. 5, also acts as a down draft baille to prevent downward drafts through the smoke pipe from reaching the `outlet of the vertical vent duct 23. This air gate with the open bottomed hood 24 forms a rectangular-shaped draft hood having well vknown functions but with the added feature of having a closable outlet. 'I'his is accomplished by combining air ,gate and baille in one member. I

As hereinbefore stated, a single gas valve is provided and; for convenient lighting, the hereinbefore described burner is located immediately Iinside a fire door 87 with the burner top level with the bottom of the iire door. Ordinarily, an operthe'l ator turns on full gas supply when lighting the burner which causes flaring out of the flame through the nre door. Therefore, means are provided which makes it impossible to turn on full gas supply while the fire door 87 is open. 'This means consists of afbell crank 88 pivoted at some point on the burner valve rotor with a link 89 connecting one end of the bell crank to the fire door, the connection being located at the proper distance from the hinge axis of the door to provide a lever which, when the ilre door 87 is opened, moves the bell crank 88 about its axis by means of the connecting link 89. 'The bell crank is so arranged that one arm `90 thereof will then be movedy so that it interferes with and prevents full movement of the arm 78 connected to the burner valve rotor and which is actuated by turning the burner valve rotor through the arm 77 attached thereto as lhas previously been described. n

In my preferred construction, the arm ,78 is provided with a projecting lug 91 in which an by interference by the lug 91 with the arm 90.

Further, this adjustment may be such that the burner valve may be turned just sufficiently for .proper ignition without havingthe flame from the burner nare out at the fire door. After ignition, the fire door is closed whereupon the belll crank arm 90 will be moved out of interference as shown in Fig. 8 and the burner valve can be turned on in full. Such construction compels a safe and ,proper ignition of the burner and the construction maybe varied so long as a means is provided for interfering with full burner valve opening until the nre door 87 is closed.

In the operation of this auxiliary furnace, secondary air for combustion enters the -space below the burner through the air inlet opening below the mixer, this air being drawn from without the gas furnace structure. The air enters the space 53 below the burner 19 and travels upwardly through the restricted slots 49, and 51 to feed the flame jets issuing from the burner. Of course,

Vit will be understood that fuel issuing from the burner has previously been ignited and the draft dampers are in open position. Combustion takes' placein the space 54 above the burner, and the products of combustion pass upwardly in the middle drum 18, divide at the top into the tubular connecting ducts`21 through which the products pass into the side drums 20.

In the side drums, the products of combustion contract and become heavier as they give up their heat, gradually gravitating to the bottom, with two o`r more side drums tending to balance. That is, if one side drum loses more heat than the other, more products of combustion gravitate throughlit` and the temperature of the burned gases at any given level are substantially alike in both side drums and are of progressively lower temperatures at lower levels.

When the combustion products are sufficiently coolto reach the bottom of the side drums 20. they pass from the bottom rear ends of the side drums into the hollow vent manifold casting 22, thence 'upwardly through the vertical vent passage 23 which vents into the open draft hood 24, and thence through an outlet opening 25 into a vent pipe that leads to the chimney of the coal furnace.

` The downward circulation of products of combustion in the side drums is due mostly to gravity because, the middle and side drums are in communication at the top, and the gases in the side draft in the vertical vent duct 23. It is true that both of these effects help the flow of the products but without a natural gravitational drop this help would not be suiiicient to maintain a free draft starting with a cold furnace, and would not be sufficient to cause movement of the burned gases away from the burner throughout its length fast enough to prevent choking of the flames and impartial combustion. In larger sizes of furnaces, employing more than one down draft drum on each side of the middle drum, andtherefore having a greater proportion of heat transfer surface extracting heat during the downward travel of the combustih products, this gravitational assistance to the normal tendency of combustion products to flow upwardly' is very pronounced.

Further, the free circulation of combustion products through the furnace make it possible to employ a rear vent passage'23 of very small rise, hence the draft hood 24 and vent outlet 25 may be low in elevation. This is important in auxiliary furnace structures because it is desirable to vent the auxiliary furnace directly into the smoke pipe of the main heating unit which is usually at relatively low elevation. This eliminates the need of a separate vent pipe to the chimney. The freedom of draft secured within the furnace makes possible, not only a low rear vent connection capable of being connected to the smoke pipe withan upward pitch between the draft hood and the I smoke pipe, but it also makes possible the restricted secondary air openings at the burner and gives a rapid pick-up of the draft when the burner is started at full capacity.

The circulation of the air to be heated through the auxiliary furnace is in an upward direction between and around the drums 18 and 20 as shown by the arrows 'in Fig. 4, the air being drawn inwardly by the fan structure hereinbefore described and forced outwardly at the top of the furnace through the outlet l1 past the air gate 69 and into the top of the main heating unit or furnace structure. It should be-noted that Just before the combustion products leave the side drums they are exposed to t'ne greatest heat extracting or cooling influence possible, that is, that of the incoming cold air.

The air around the side drums flows in a direction opposite to that of the combustion products within the side drums which results in progressively greater heating influence upon the air as it travels upwardly and progressively greater L cooling influence upon the combustion products as they travel downwardly. Just before the air reaches the furnace structure opening 11, it is exposed to the influence of the hottest heating surface with the result that the greatest average temperature difference exists between .the heating surface and the air which is possible to achieve upon a practical This, in turn, results in the greatest possible heat transfer per square unit of the heating -surface. Such direct and practically unimpeded upward flow of the air to be heated provides a strong air circulation which is a very desirable feature in an auxiliary furnace.

With the construction above described it is possible to use either the main heating unit or the auxiliary furnace alonel or use them simultaneously arid in combination. In using the main heating unit alone the gate controlling the flow of hot air to the main heating unit is closed as well as the combustion draft dampers o f the auxiliary furnace. In using the auxiliary furnace alone, no change is made inthe main heating unit inasmuch as the -iiow of heated air is upwardly and directed into the main heating unit at substantially the point at which heated air is removed from the main' heating unit to be delivered to the room register or other equipment.

What I claim is:

1. In combination with a main furnace of the warm air type, an auxiliaryv warm air furnace comprising a* casing including a front panel, a back panel, interchangeable side panels, said front, back and side panels being adapted to ilt together at their adjoining edges, an air heating means within said casing, and a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace.`

2. In combination with a main furnace of the warm air type, an auxiliary warm air furnace comprising a casing including a front panel, a back panel, interchangeable side panels, 'said front, back and side panels being. adapted to nt together at their adjoining edges, an air heating means within said casing, va warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace, and a closure for said warm air outlet.

3. In combination with a main furnace of the warm air type, an auxiliary warm air furnace comprising a casing including a front panel, a back panel, interchangeable side panels, said front back and side panels being adapted to fit together at their adjoining edges, an air heating means within said casing, a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace, a closure for said warm air outlet, and thermostatic means for causing opening o! said closure under the influence of heat.

4. In combination with a main furnace of the together at their adjoining edges, air heatingmeans within said casing, a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace,y and a cold air inlet in one of said interchangeable side panels.

5. In combination-with a main furnace of the warm air type,. an auxiliary wann air furnace comprising a casing including a front panel, a back panel, interchangeable side panels, said front, back and side panels being adapted to fit together at their adjoining edges, air heating means within said casing, a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace, and a cold air inlet in one' of d interchangeable side panels and adapted for duct communication with the interior of said main furnace.

6. In combination with a main furnace of the warm air type, an auxiliary warm air furnace comprising a casingA including a front panela back panel, interchangeable side panels, said front, backand side panels being adapted to fit together at their adjoining edges, air heating means within said casing, 4a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace, and a cold air inlet in one of saidI interchangeable side panels and adapted for duct` communication with the lower interior of said main furnace.

7. In combination with a main furnace of the warm air type, an auxiliary furnace comprising a casing including a front panel, a back panel, interchangeable side panels, areversible top panel, said front, back and side panels being adapted to flt together at their adjoining edges, an air heating means within said casing, and a warm air outlet in one of said interchangeable side panels adapted for duct communication with the interior of said main furnace.

8. In combination with a main furnace of the warm air type, an auxiliary furnace comprising a casing including a front panel, a back panel, interchangeable side panels. a reversible top panel, said front, back and side panels being adapted to t together at their adjoining edges, an air heating means within said casing, a warm air outlet in one of said .interchangeable side panels and adapted for duct communication with the interior of said mainfurnace, anda cold air 'inlet in said casing.

, 9. In-combination with a main furnace of the warm air type, an auxiliary furnace comprising a casing includingia front panel, a backv panel, interchangeable side .i panels, a top panel, said front, back and side panels being adapted to llt together at their adjoining edges, an ai'r heating -means within said casing and supported exclusively by said front and back panels, and a warm air outlet in one -of said interchangeable side panels and adapted for duct communication with the interior of said main furnace.

10. In combination with a main furnace of the Warm air type, an auxiliary furnace comprising a casing including a 'front panel, a back panel, interchangeable side panels, a top panel, said front, back and side panels being adapted toflt together at their adjoining edges, an air heating means within said casing and supported exclusively by said front and back panels,'a warm air outlet inv-one of said interchangeable side panels and adapted for duct communication with the interior of said main furnace, and a cold air inlet in said casing. y

11. In combination with a mainvfurnace of the Warm air type,an auxiliary warm air furnace comprisinga casing including a frontpanel a backpanel, interchangeable side panels, said front, back and side panels-being adapted to fit together at their ladjoining edges, an air heating means within said casing, a warm air outlet in one of said interchangeable side panels vpanel being inclinedupwardly toward said warm and adapted for duct communication with .the interior of said main furnace, and a reversible closure for said warm air outlet.

12. In combination with a main furnace of the warm air type, an auxiliary furnace comprising a casing including a front panel, a back panel, interchangeable side panels, a reversible top panel, said front, back and side panels being adapted to fit together 'at their adjoining edges, an air heating means within said casing, and a warm air outlet in one of said interchangeable side panels and adapted for duct communication with the'interior of said main furnace, said reversible top panel being inclinedv upwardly toward said warm air outlet.

13. In combination with a main warm air furnace, an auxiliary warm air furnace comprising a casing including a front panel, a back panel, interchangeablev side. panels, said front, back and side panels being adapted to fit together at their adjoining edges, an air heating means within said casing, and a cold air inlet and a warm vair outlet in one of said interchangeable side panels, said warm air outlet having duct communication with the interior Vof said main furnace.

14. In combination with a main warm air furnace, an auxiliary warm air furnace comprising a casing including a front panel, a back panel, interchangeable side panels, said front, back and side panels being adapted to fit together at their' adjoining edges, an air heating means within said casing, and an air inlet and a warm air outlet in one' of said interchangeable side panels, both said inlet and said outlet having duct communication with said main furnace.

15. In combination with a warm air heating furnace', an auxiliary warm air furnace comprising a casingincluding a front panel, a back panel, interchangeabieside panels, said front, back and side panels being adapted to fit' together at their adjoining edges, an air heating means Within said casing, an air inlet and a'warin air outlet in one of said interchangeable side panels, both said inlet and said outlet having duct communication withl said main furnace, and an air moving means in said aix` inlet duct. l

16. An auxiliary .warmvair furnace, comprising a casing including front and back panels, interchangeable side panels of equal height, a reversible top panel, a heating means within said casing, f and a warm air outlet in one of said interchangeable side panels and adapted for duct communication with a main warm air furnace, said top air outlet.

17. In combination with a main warm air furnace, an auxiliarywarm air furnace comprising a casing, an air heating means within said casing, an air inlet to said casing, a warm air outlet therein, ducts connecting said air inlet and said warm air outlet with the interior of said main furnace, and an air flow accelerating means for said auxiliary furnace including a fan structure in said air inlet duct, said fan structure being reversibly mounted on a supporting frame and being withdrawable as a unit from said duct.

l o'r'ro J.- KUENHOLD.

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