CA1092923A - Heating apparatus having improved combustion - Google Patents

Abstract

ABSTRACT OF THE INVENTION
A wood-burning heating apparatus, used as a parlor stove, and providing a significant heat output is disclosed. The stove has primary and secondary combustion chambers and a baffling arrangement for directing flue gases along a circuitous path to the exit aperture whereby a significant proportion of the heat of said gases is given up to the apparatus. A vertically oriented downwardly directed baffle separates the combustion chambers. Primary and secondary air paths supply air to the primary and secondary combustion chambers respectively. Each of the supply conduits is pre-heated and the secondary air supply provides oxygen substantially evenly around an opening at a bottom portion of the baffle to increase the efficiency of secondary combustion. The apparatus is further provided with a self-clearing top smoke chamber having a pivotable top cover. A rotatable flue collar is provided for either a horizontal or a vertical connection to the exit flue.

Description

Z~3Z~ ' The invention relates generally to heatiny apparatus and in particular to a wood-burning heating apparatus having a high heat conversion efficiency.
This is a division of copending Canadian Patent ApplicatLon Serial No. 298,366, filed March 7, 1~78.
Wood-burning stoves have been availa~le for centuries. Perhaps the most well--known wood-burning stove is the Franklin stove which, while being practical for i-t~
time, burned wood inefficiently. That stove, like most cast iron stoves available today, provides for upara~t combustion, such as is ound in a fireplace and in which the volatile , .
gases (volatiles) which are driven off as the wood burns are generally left unburned. The unburned volatiles remain .. . .
for two reasons, first because the gases, by the time they have left the wood, are generally too cool or secondaxy combustion and second, because oxygen that is admitted to the stove or fireplace lS usually consumed by the coals at the base of the fire mass, causing the gases to rise through an oxygen-deficient atmosphere. The loss of the volatile 20 gases is a serious problem, because they represent approximatel~ ;
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half of the total heat value of the wood. It is as though one were;to run an open line-of natural gas up a chimney without bothering to ignite it first. In addition, the . ~ - . ~ .
~- volatile gases fiven off from the wood without being ignited ;~ may also condense on the cool sldes of long metal flue pipes and drip out as creosote which may sometimes be inadvertently and dangerously burned, in their sold creosote form, as a chimney fire.

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tZ3 One effective method and apparatus for reduciny the volatiles is found in a horizontal combustion heating appar~-tus wherein the flames move horiæontally in the primary combustion zone. This is radically different from typical updraft com-bustiQn and is the~basis of the mo:re efficient operat~on of a stove manufactured by Vermont Ca~tings, Xnc.,-the assignee of this invention, which has been sold since at leas~ the first q.uarter of 1976 under the trade name 'IDEFI~NT". The DEF~NT
parlor stove aids t~e burnîn~ of t~e ~olatile gases in several ~ays. First, by using horizontal combustion, the ~ases are forced to pass close to t~e hot coals ~h~ch maintain suf~iciently high temperatures to ignite ~hém. In addition, a manuall~
controlled secondaxy air sou~ce, which i5. segregated from primary air sou~ce~ provides aix w~ich. is ducted down a tube integral with the heated fireback of the primary combustion chamber, which.is heated by the hottest.part of the fire on two sides, and this channel preheats the air to maintain the air at the elevated temperatures requirad for combustion~ Thus, oxygen from the secondary source is led into the secondary combustion chamber through numexous air ports to mix with the combustible gases and to provide secondary combustion. In the "DEFIANT", the secondary souxce of air is provided in the secondary combustion chamber.along an outside wall of the chamber, away from the primary combustion chamber.
In addition, behind the fireback which is provided at the back of the primary combustion chamber, a circuitous path is provided by smoke baffles. The circuitous pa-th is comprised of a plurality of smoke passages, which conduct the smoke through the passages back and forth along the back of the apparatus and , , . "

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upwardly toward the exit at the flue collar. Since the heat of the flue gases is considerable, significant heat transfer occurs from the flue gases to the surfaces of the stove, which in turn is given off into the room rather than being lost up the chimney. In addition, the circuitous path aids in maintaining higher temperature in the combustion chamber which aids in burning the volatile gases driven off from the wood. Thus, in the "DEFIANT", a large heat output is available.
In addition, the fire is controlled by not only the structure of the apparatus but by a thermostatically controlled input port which supplies the primary air.
Even though, the "DEFIANT" promotes secondary combustion in the secondary combustion chamber, it is still desirable to increase the efficiency of the unit by whatever - means are needed. Thus, while the "DEFIANT" has been hailed as a significant advance in the art of building wood-burning stoves, there should always be room for further improvement.
It is therefore a principal object of this invention to provide a heating apparatus having improved secondary combustion.
Yet further objects of the invention are to provide a wood-burning apparatus which is reliable, which provides efficient operation, which is capable of long-term operation with a single load of wood, which has a high heat output.

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29~3 According to the present invention there is provided a wood-burning heating apparatus having a heat conducting frame member enclosing a primary combustion chamber and a secondary combustion chamber in gaseous communication with the primary combus-tion chamber. A
baffle arrangement is in yaseous communication with the secondary combustion chamber for providing a long inkernal flame path. A vertically oriented, downwardly directed baffle is provided for separating the primary and secondary combustion chambers, a portion of the baffle being spaced from a bottom surface of the frame for providing an opening connecting the primary and secondary combustion chambers for providing the gaseous communication therebetween. A
primary air supply path provides air for promoting combustion in the primary combusti~ chamber, the primary air path in the primary combustion chamber being defined by a slotted air tube conduit including, in cross section, a J-shaped horizon-tally directed portion extending from a vertical wall of the frame and an upwardly directly vertical portion directed to intersect, if extended, the J-shaped portion. A conduit products exit aperture is provided at a top portion of the frame and in gaseous communication with the baffling arrange-ment for providing a~ exit port for combustion products.

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~0~3329~3 DESCRIPTION OF T~LE DRAI~INGS
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Other features, objects r and advantages of the invention will appear from the following description of a preferred embodiment taken together with the drawings, in ~hich:
Figure 1 is a front perspective view of a heating apparatus according to the invention, Figure 2 is a rear perspective view of the heatiny apparatus of Figure l;
Figure 3 is a cut-away front perspective view of the heating apparatus according to the invention;
Figure 4A is a cross-sectional schematic view of the rotatable flue collar in the rear exit position;
Figure 4B is a cross-sectional schematic view of the rotatable flue collar in the top exit pos~-~ion; ;~
Figure 5 is a cross~sectional view facing the back of the fireback baffle along lines 5-5 of Figure 3;
Figure 6 is a cross-sectional view taken along lines 6-6 of Figure 5.
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~: ~ 2a Figure 7 is a cross-sectional view taken along lines 7~7 of Figure 3; and Figure 8 is a cross-sectional view taken along lines 8-8 of Figure 5.
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~Z9~3 DESCRIPTION OF A PREFER~ED EMBODIMENT
... .. . . _ Referring to Fi.gure l,the wood-burning heating apparatus 8 has an exterior frame member 10 preferably comprised of a heavy-duty cast iron. The sides 12a, 12b, front 12c with doors 12e, 12f, back 12g, top 12h, and bottom 12i of the frame member are joined to form an integral air tight unit. The front pivoting doors 12e, 12f, allow the heating apparatus to be opened Erom the front for both loading of wood and for ~iewing the ire when the heating apparatus is used as a fireplace. A top cover 14 of the apparatus, has hinges 15a, 15b which allow it to pivot to an upward position, whereb~ wood may be loaded into a primary comkustion chamber 16 (Figure 3~ through a smokeless loading aperture 1~.
The aperture size is designed to sweep the openiny clear of smoke when the top cover is pivoted to an open condition.
Preferably the ratio bf aperture cross-sectional area to the flue gas output exit c~oss-sectional area is about three to oneO Thus, e~en when the stove is in operation, firewood ~ may be reloaded merel~ by droppong wood into the primary 20.~ combustion chamker. An asbestos seal around aperture 17 . .
provides an air tight fit between cover 14 and the frame member.
Referring to Figures 2 and 3, air is fed to the primarX comkustion chamber 16 through a primary inlet port 18 and a primar~ air supply flow path 20 (Figure 3~. Inlet port 18 is thermostatically controlled by a thermostat 21 which operates a damper 22 covering an aperture 23 (Figure 6) in the back frame member 12g. Thermostat 21 is for example an 8" coil of bimetallic material connected to damper 22 b~
a flexible chain 24. Heating apparatus 8 is also provided with a damper control lever 25, a rotatable flue member 26, and tm/ 6 .l~g~23 n~mually controlled night air inl~t port 27 in side m~mb~r 12a.
ReEerring to Figure 3, primary air extending through aper hlre 23 travels through primary air supply path 20 and is heated ~
by the fire which sur.rounds the tubes. m us, the prim~ry air is preheated and helps to keep a hotter fire going with less air and wood consurned.
r~he primary combustion cha~ber is bounded b~ the substantially ver~ieally oriented downwardly extending fireback baffle 28, the side walls 12a rmd 12b of the frame m~mber, the front doors 12e, 12f and front wall 12c of the frame me~ber and the top 12h and bottom 12i frame member Ekanels.
A right-hand portion 29, of baffle 28 further provides a partial separation between the primary combustion chamber 16 and a secondc~ry c~bustion ehamber 30. rrhe secondary ccmbustion chamber is connected to and is in gaseous cGmmunication with the primary ccmbustion chamber through an opening 31 in baffle 28 . A secondary air supply flow path 32 is provided, for the secondary ccmbustion,chamber f~om thermostatically controll~d inlet port 18, and comprises an imperforate section 36 (Figure 5) which e~tends from the inlet port 18 to substantially the beginning of the secondary oombustion cha~ber and a perforate or apertured conduit 38 which extends within the secondary ecmbustiol.l chamber along a bottQm section of baffle 29 around open~i~ 31. The detailed nature of the secondary air supply is descriked in ~ ~ more detail below.
: There is further provided a third air supply path 40 which,may be used to provide air from manually con-trolled inlet 27 to the seeondary ccmbustion chamber during night or other selected periods of low heat ~ output operation. Air supply path 40 further provides additional oxygen : for secondary ccmbustion in the secondary .
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~O~Z923 ,combustion chamber.
Behind the firehack baffle 28 are a plurality o~
connecting smoke passages 104, 106, 108 lFigure 5). These passages direct the spent flue gases from the secondary combustion chamber to the left encl of the apparatus, ~lookiny from the front), then into an upper channel or passage 41b and back toward the right portion of the sto~e, and then further up into an uppermost passage 41c and back toward the left portion of the stove, where the~ finally exit through the flue collar 26. The secondary combustion chamber, taken together with the smoke passages, make up the flarne path.
Since the heat of the flue gas is considerable and is trans-ferred to the surfaces of ~he stove as the flue gases traverse the passages, a significant amount of heat is given of~ to the room rather than being lost up the chimney. In addition, 9 ' .
since the passayes are adjacent to the primary combustion chamber higher temperatures are maintained with;n the fire mass itself, which aids in burning the vola-tile gaseous products from the burning wood.
~The heating apparatus, which is described above : . . . , -and incorporates the pivoted top cover, i~ also disclosed and is claimed in copending Divisional application Serial .
No. 351,033, filed May 1, 1980.
Re~erring to Figures 4A and 4B, flue collar 26 is preferably rotatable to allow operation o~ the apparatus with either a horizontal exit ~Figure 4A) or a vertical exit (~igure 4B) position. The flue collar is attached to an inclined back portion 50 which is securely positioned on the back and top frame portions of the apparatus. The flue cbr/~S

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Referring to Figure ~A, an extended portion 60 of the flue collar contact vertically oriented section 62 of the back portion 50 for additional orientation and alignment support. By removing the flue co:llar bolts, (Located on opposite sides of the flue~, and rotating the flue collar 180t the orientation shown in Figure 4B may be obtained.
This oxientation provides the top exiting stove and is main-tained by replacing the bolts 56. The ext~nded portion 60 of the flue collar 26 is now positioned against the horizon~
-tally oriented section 64 of portion 50.
The heating apparatus, which is described above and incorporates the rotatable flue collar is disclosed and is also claimed in copending Divisional Application Serial No. 351,034, filed May 1, 1980. ~ .
Referring to Figures 5 and 6, the thermostatically controlled inlet port 18 preferably supplies air for both the primary and secondary air flow paths. Ambient air enter~
through aperture 23 in frame back wall 12g and is almos-t immediately divided between the primary and secondary flow paths by a dividing plate member 70. That portion of the .
incoming air which passes into -the secondary flow path 32 is .
~ directed along the fireback baffle 28 and is constrained to - . ~ . .
follow a path adjacent to the fireback baffle by an enclosing .member 72. Enclosing member 72 not only directs the secondary : air flow toward opening 31 in baffle 28, but, in order to : provide a substantially uniform flow of air into opening 31, .
the cross-sectional area of the supply path defined by en-closing member 72 in combination with baffle 28 increases substantially as the path approaches the opening, as shown in :~ :
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~2~23 Figure 5. This provides the necessary volume distribution of the flow to promote substantially uniform air flow in the opening. At the opening 31, the enclosing member 72 ends in a substantially spaced apart parallel alignment with the baPfle 28, for example at 80 (Figure 3) so that the flow of secondary air is substantially unimpeded into the secondary chamber at opening 3]. The secondary air supplied at opening 31 is also preheated due to its proximity with baffle 28 so that the efficiency of the secondary combustion chamber is increased.
The heating apparatus which is disclosed above and incorporates the preheated secondary air supply path is also disclosed and is claimed in the above-identified parent application Serial No. 298,366.
That portion o~ the ambient air passing through aperture 23 which follows primary flow path 20 according to the present invention, passes through the baffle 28 near the lower base of the baffle ~Figure 3) and is supplied to the primary combustion chamber along an open ended slotted conduit which extends from baffle 28, along side wall 12a, and for approximately one-fifth the distance along the bottom of front wall 12c. The slotted conduit has a cross-sectional area which is substantially constant (Figure 7). The conduit comprises a horizontally extending J-shaped element 84 and a vertically upwardly extending cast member 86 which together define the elongated slot 88. Primary air is thus provided to promote a uniform flow of combustion supporting oxygen across the entire depth of the combus-tlon chamber.
Thus the air provided by primary flow path 20 enters :
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~ )9~Z3 the primary combustion chamber along the bo-t-tom left-hand surface oE the chamber (looking from the front), and traverses the chamber toward the right-hand side panel 12b, providing combustion along the entire bottom of the wood supply. Upon reaching the right-hand portion of the apparatus, the air flow .~s directed toward and through opening 31 and exits thxough the circuitous flow path provided hy the ba~fle arrangement extending between baffle 28 and rear wall 12g.
Referring to Figures 5 and 8, the baffle arrangement . for directing the flue gases along the circuitous path through the space between baffle 28 and back wall 12g comprises a lower baffle 90 and an upper baffle 92. Lower baffle 90 is comprised of two cast plate members 94 and 96 which meet along their length to form baffle 90 when the fireback baffle 28 is put into position. Baffle 90 extends substantially from side wall 12b to a position near side wall 12a. Baffle 92 extends above baffle 90 and comprises a pair of tabular cast supporting members 98, 100 which support a baffle plate 102 ~ axtending substantially from side wall 12a to a position near side wali 12b. The flue gases thereby are directed from a ~ first horizontally directed passage ].04 to a second horizon-.: tally directed passage 106 and then to a third horizontally directed passage 108 from which they exit through flue collar 26.
The heating apparatus is also provided with a damper 110 which enables the apparatus both to be used as a parlor stove and as a fireplace. In the position shown in Figure 8, the apparatus can be used as a fireplace with the flue gases exiting from the primary combustion chamber along a path , .

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~enerally ind.ica-ted by arrow 114. This provides updraE-t combustion. When the damper is closed, that is, placed in a position indicated by dotted line 116, the heating apparatus operates as a stove and the flue gases exit substantially as shown by the arrow 120 (Figure 3). (When fuel is loaded into the apparatus through top cover member 14, the flue must be in the closed position or otherwise smoke will pour out of the aperture 17 in the top panel 12h).
Referring to Figures 2 and 8, back wall member l~g has a series of corrugations 122, 124, 126, which protrude : outwardly from the plane of back wall member 12g. ~hese corrugations provide additional heat radiation surfac~s for the heating apparatus for increasing the heat delivery to the surrounding air.. In addition, the corrugations provide con-venient means for chane]ling "night air" from the manually controlled inlet port 27 to the secondary combustion chamber :~ through night air flow path 40. Thus, the lowermost cor-rugation 126 is blocked off by a plate 130 and is used to ~: ~ channel the ni.ght air into or at least towards the secondary combustion cha~er.
: ~ ~ The heating apparatus, which is described above ~ ~ and incorporating the corrugation shaped back panel is also :
described an~. is claimed in copending Dlvisional application Serial No. 351,036, filed May 1, 1980.

: ~ In the preferred embodiment of the invention, the :
:: opening 31 has a height of between 3 and 4 1/4 inches and :: ~ is preferably 4 inches high.~ It has been found for the : ~ : particular apparatus depicted in Flgure 3, that the height :~: of opening 31 is important and a height substantially greater : cbr/ ~lB

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,, ` . . . -. . .... .. .. .. . .` ' 9~3 than 4 inches increases the he~t output oE the apparatus and also its conversion efficiency.
The described apparatus, while designed primarily for wood-burning applications, can also be adapted for coal burning. A basket-shaped container of coal can be inserted through top aperture 17. The basket rests on the bottom 12i of the frame and the coal is then burned in substantially the same manner as when the stove is used to burn wood.
There is thus provided a compact wood-burning heating apparatus having an exceedingly high efficiency due both to its secondary combustion chamber and secondary air supply supporting it, as well as to its long flue gas flow path and horizontal combustion. It would be obvious to one skilled in the art to apply the various features of the preferred embodiment to a larger wood-burning heating apparatus such as the "DEFIANT" referred to abov~, wherein the secondary combustion chamber exists alongside of and not behind the primary combustion chamber.
~ Other embodiments of the invention, including additions, subtractions, deletions, and other modifications of the preferred embodiment of the invention will be obvious to one skilled in the art and are within the scope of the following claims.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A wood-burning heating apparatus comprising a heat conducting frame member enclosing a primary combustion chamber, a secondary combustion chamber in gaseous communication with said primary combustion chamber, and a baffling arrangement in gaseous communication with said secondary combustion chamber, for providing a long internal flame path, a vertically oriented, downwardly directed baffle for separating said primary and secondary combustion chambers, a portion of said baffle being spaced from a bottom surface of said frame for providing an opening connecting said primary and secondary combustion chambers for providing said gaseous communication therebetween, a primary air supply path for providing air for promoting combustion in said primary combustion chamber, said primary air path in said primary combustion chamber being defined by a slotted air tube conduit comprising, in cross section, a J-shaped horizontally directed portion extending from a vertical wall of said frame and an upwardly directed vertical portion directed to intersect, if extended, the J-shaped portion, and a combustion products exit aperture at a top portion of said frame and in gaseous communication with said baffling arrangement for providing an exit port for combustion products.