CA1076441A - Heating apparatus having improved combustion - Google Patents

Abstract

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 baffle system for directing flue gases along a circuitous path from the secondary combustion chamber to an 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. First and second air paths supply air to the primary and secondary combustion chambers respectively. The air provided by the supply conduits to the respective combustion chambers is preheated and the air provided through the second path promotes secondary combustion of the flue gases to thereby increase the overall efficiency of the stove.

Description

IIE~T~NG APPARATUS fl~VI~G IMPROVED COMBUSTION

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 baffle system for directing flue gases along a circuitous path from the secondary ;~
combustion chamber to an exit aperture whereby a significant proportion of the heat of said gases is given up to the apparatus. A vertically oriented downwardly . . .~ .
10 directed baffle separates the combustion chambers. First and second air paths supply air to the primary and secondary ~ -~
combustion chambers respectively. The air provided by the ~;
supply conduits to the respective combustion chambers is preheated and the air provided through the second path '~
promotes secondary combustion of the flue gases to thereby ._., , - 1:' -increase the overall efficiency of the stove.

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The invention relates generally to heating apparatus and in particular to a wood-burning heatiny apparatus having a high heat conversion efficiency.
This is a division of copending Canadian Patent Application Serial No. 298~050, filed March 2, 1978.
Wood-burning stoves have been available for centuries. Perhaps the most well-known wood-burning stove is the Franklin stove which, while being practical for its time, burned wood inefficiently. That stove, like most cast iron stoves available today, provides for updraft combustion, such as is found 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 for secondary combustion and second, because oxygen that is admitted to the stove or fireplace is 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 hot, unburned volatile gases is a serious problem, because they represent approximately 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 given off from the wood without being ignited may condense on the cool sides of long metal flue pipes and drip out as creosote which may sometimes be inadvertently ~ ~`
and dangerously burned, in their solid creosote form, as a chimney fire. -It is therefore a principal object of this ;
invention to provide a heating apparatus having improved combustion efficiency ~, ' '"' ' - 1 - , sb/~

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Yet further objects of the invention are to provide a wood-burning apparatus which is reliable, which is simple to operate, which is capable of long-term `
operation with a single load of wood, which has a high heat output.
According to the present invention, there is provided a wood-burning heating apparatus having a heat conducting frame member enclosing a primary combustion chamber, a secondary combustion chamber in gaseous communication with the primary combustlon chamber, and a baffle system in gaseous communication with the secondary combustion chamber, for providing a long internal flame ;
path. A vertically oriented, downwardly directed baffle is provided for separating the prlmary and secondary combustion chambers, the baffle being in combination with ithe frame member for providing an opening connecting the primary and secondary combustion chambers and for providing the gaseous communication therebetween. A primary air supply path provides preheated air for promoting combustion , ~ .
in the primary combustion chamber. There is provided a pivoting side door, and baffle means for providing a smoke- -less loading aperture in the frame member when the door -is pivoted to an open condition. A combustion products ; ;
exit aperture is provided at the top portion of the frame ~-and in gaseous communication with the baffle system for providing an exit port for combustion products.
In a specific embodiment of the invention, the baffle means includes a vertical panel extending parallel to a side of the frame member between~the primary chamber and a back wall of the frame member, the panel being positioned adjacent the side having the door.

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10~441 DESCRIPlION OF TIIE DRAWINCS

Other features, objects, and advantages of the invention will appear ~rom the following description of a preferred embodiment taken together with the drawings, : ~ :
in which:
Figure 1 is a front perspective view of a heating apparatus according to the invention;
Figure 2 is a back perspective view of the heating apparatus of Figure l;
Figure 3 is a cut-away front perspective view::
of the heating apparatus according to the invention;
Figure 4 is a cross-sectivnal view taken along lines 4-4 of Figure 3; and Figure 5 is an enlarged view of the circled are~ of Figure 4. ~ :

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_. , ' , ` ~ ', ' ' ' _ 3 _ ; , , 10~76441 DESCKIPTION OF A PREFERRED EMBOl)IMENT
_ General Descr_ ~tion Referring to Figure 1, a wood-burning heating apparatus 8 has an exterior frame member 10 pre~erably 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 in a channeled -construction to ~orm an integral, air-tight unit. The front pivoting doors 12e, 12f, allow the heating apparatus to be opened from the ront for both loading of wood and for viewing the fire when the heating apparatus is used as a fireplace. A pivoting side door 14 of the apparatus~
has hinges 15a, 15b which allow it to pivot abou~ a vertical rotation axis, whereby wood may be loaded into a primary ~ ~
combustion chamber 16 (Figure 3) from the side o the ~ -apparatus. In its closed position, door 14 seals against a gasketing material such as a one-quarter inch diameter asbestos rope sealing member. Door 14 interlocks with a damper 18 (Figures 3 and 4) whose position is controlled - 20 by a handle 20 so that the door can be fully opened only when the apparatus is in an updraft combustion configuration .
as described in more detail below. Illu$trated top meniber 12h supports a cast iron cooking surface 21.
Referring to Figures 2 and 3, air is supplied to the primary combustion chamber 16, through a primary inlet port 22, by a primary air supply flow path having branches 24a, 24b (~igures 3 and 4). Inlet port 22 is thenrlostatically controlled by a thel-lTIostat 26 whieh operates a pivoting damper 28, removably covering an ~ 30 aperture 30 in the back frame member 12g. Thermostat 26 ' _ 1~7 ~

is for example an 8" coil of bimetallic material connectecl to damper 28 by a flexible chain 32. Heating apparatus 8 also has a damper control lever 34 for regulating thermostat 26. A manually controlled night/
secondary air inlet port 35 in side member 12a provides the air inlet for air supplied to a secondary combustion ~ ;
chamber 36 (Figure 3) through a secondary air flow path 37.
Referring to Figure 3, primary air entering through aperture 30 travels through primary air supply paths 24a, 24b and is heated by contact with the hot walls which define the supply paths 24a, 24b. Thus, the primary air is preheated and therefore helps to keep a hotter fire going with less air and wood being consumed. The primary combustion chamber is bounded by the substantially ;
vertically oriented downwardly extending fireback baf~le 38, side door 14 and side wall 12a of the frame member, the -front doors 12e, 12f and front wall 12c of the frame member, the top 12h and bottom 12i ~rame member panels, and a vertically oriented interior panel 40 which separates the primary combustion chamber rom the secondary combustion chamber 36. ;;
The secondary combustion chamber îs connected to : ;
and is in gaseous communication with the primary combustion `~
chamber through an opening 44 in panel 40~ Illustrated opening 44 is defined by the panel 40 in combination with the frame members, here the bottom and front rame members.
The secondary combustion chamber is bounded by the vertically oriented panel 40 in combination with fraTne members 12b, 12c, 12g, 12h, and 12i. As noted above, the secondary combustion chamber receives preheated air from the air inl~t port 35 , . . .
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~ ` 1076~1 through the secondary ai.r supply flow path 37 The flow path 37 comprises an imperforate section 48 which .
extends between the inlet port 35 and panel 40, and a perforate section 49 extending from panel 40 into the secondary combustion chamber.
The Flame Path Behind the fireback baffle 38 are a plurality of connecting smoke passages 50~ 52 which provide a circuitous path from the secondary combustion chamber to the flue . ~;
ex;t opening at flue collar 58. These passages direct ~ ~
the spent flue gases from the secondary combustion .~ -chamber-to the left end of the illustrated-apparatus through passage 50, then upward into the upper channel .
or passage 52 back toward the right-hand portion of the :~
stove, where they exit through the 1ue collar 58~
The secondary combustion chamber, taken together .. with .the smoke passages, make up the flame path. Since .,,, ,.: :
the heat of the flue gases is considerable, and is trans-ferred to the surfaces of the stove as the flue gases traverse the passages, a significant amount of heat is given off to the room, especially through the side and back rame members, rather than being lost up the chimney In addition, since the passages.are adjacent to the primary combustion chamber, higher temperatures are maintained within the fire mass itself, which aids in burning the `
volatile gaseous products escaping rom the burning wood.
The illustrated flue collar 58 is attached to the .
top panel 12h and provi.des a vertical or top exit for the .
spent flue gases. ~n other embodiments of the invention~
the flue collar can be attached, for example, to an upper - 6 - :

portion of back panel member 12g to provide a rear '~
exit for the El~e gases.
The Primary Air Flow Path As noted above~ the thermostatically controlled inlet port 22 supplies air for the primary air flow path.
Ambient air enters the apparatus through aperture 30 in frame back wall 12g and almost iT~nediately divides between the side branch 24a and the back branch 24b. That portion of the incoming air which passes into the back branch 24b is directed along the back o fireback baffle 38 and is ;
constrained to follow a path adjacent to the fireback , baffle by an enclosing member 64. Fireback baffle 38 ,~
has a plurality of ho~e~ 66 extending therethrough for providing preheated primary air to the back of the primary ' combustion chamber. Illustrated enclosing member 64 LS a ,, cast iron plate and branch 24b has a substantially constant cross-sectional area along its length. ','~
That portion of the ambient air passing through ''-aperture 30 which follows side branch 24a passes through the baffle 38 at a lower section of the baf1e' (Figure 3) and is directed into the primary combustion chamber along ~ ,' a periodicall~ slotted conduit 68 which extends from baffle 38, along,side wall 12a (below side door 14) and for ', approximately one-fifth the distance along a bottom section of front wall 12c. The slotted conduit has a cross-sectional ar,ea which is substantially constant and ispartially open at i~
end 70. Primary air is thus provided to promote a uniorT,n ~ ~ -flo~ of combustion supporting ox~ygen across the entire primary combustion chamber.
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1~7 ~ ~41 I~e air provide~ by primary flow branches 24a and 24b thus enters the primary combustion chamber along the bottom back and bottorn le~t-hand boundary surfaces of the cha~ber (looking ~rom the front), and provides combùstion along the entire bottom of the wood supply.
Upon reaching the right-hand portion o~ the primary combustion chamber, the air flow (now containing volatiles) continùes through opening 44 into the secondary combustion ~ :
chamber and exits through the circuitous flow path provided ~ -by the back baffle system arrangement extending between ~:
baffle 38 and rear wall 12g. ~ .
Details of the Back Baffle System Referring to Figures 3 and 4, the back bafflesystem for directing the flue gases along the circuitous path through the space between baffle 38 and back wall 12g .. consists of a lower baffle 90, an upper baf1e 92, and a vertical plate member 94. Illustrated lower baffle 90 consists of a cast plate member which extends in a :
transverse direction between the fireback 38 and the back wall.of the frame. Illustrated baffle 90 extends ~:
lengthwise from the substantially triangular shaped, - :-vertical plate member 94 to the vertical panel 40.- Plate member 94 extends transversely between the fireback 38 an~
back wall 12g and vertically from a level near the bottom : ~:
of door 14 (preferably from lower baffle 90) to a :
position above the top of door 14 (and preferably to the upper baffle 92). Triang-~lar plate 94 provides a barrier to prevent flue gases in the space behind tlle fil.ebaclc from escaping through an opened side door.

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1()7~41 The upper baEfle 92 extends above baff].e 90 and consists of a cast plate member extending from vertical baffle 40 to a position near side wall 12a. Baffle 92 thereby creates an aperture 96 so that the flue gases pass from the lower horizontally directed passage 50 through aperture 96 to the upper horizontally directed passage 52 from which they exit through flue collar 58.
The Damper The damper 18 of the heating apparatus enables the apparatus to be used both as a parlor stove and as a fireplace. When the damper is in the substantially vertical position shown in Figure 4, the heating apparatus operates as a stove and the flue gases exit substantially as shown by the arrow 98 (Figure 3). When the damper is placed in . :
a substantially horizontal position indicated by dotted lines 100 (Figure 4), the apparatus can be used as a fire~
placed with the flue gases exiting from the primary combustion chamber along a path generally indicated by arrow 102. This provides updraft combustion.
When fuel is loaded into the apparatus through :
side door 14, the flue must be in the closed position (the damper in a horizontal position) or otherwise, smoke will pour out of door opening. An interlocking arrangement between the door 14 and the damper 1~ ensures that the flue is closed before the side door 14 can be fully opened. The illustrated arrangement consists of a handle 20 on the damper which is in the vertically downward position and engayes door 14 if the door is opened and the flue is not closed. Other arrangements can also be used.
The above-described heating apparatus having the pivotable damper is also described and is claimed in copending divisional application Serial No. 330,772, filed June 28, 1979.
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In an embodirnen-t of the invention, the opening 44 may have a height of between 3 and 5 inches and is ~ -preferably 4 1/2 inches high. It has been found for the particular apparatus depicted in Figure 3, that the heiyht of opening 4~ is important and a height substantially greater than ~ 1/2 inches increases the heat output o~
the apparatus and also its conversion efficiency.
To further control combustion within the heating apparatus, the illustrated frame members are interconnected along their edges in a channeled construction (Figure 5).
The channeled construction consists of a cast groove 130, at the edge 131 of one of the joining members, which receives a layer 132 of plastic sealing material, for example an asbestos gasketing material, and the other joinîng member 133. This construction provides an airtight, physically secure and rigid structure.
The above-described heating apparatus including the channeled construction is also described and is claimed in copending divisional application Serial No. 330,773, filed June 28, 1979.
The present invention provides an effective apparatus for reducing the volatiles found in typical up-draft combustion by providing a horizontal combustion heating apparatus wherein the flames move horizontally in the primary combustion zone. This is radically different from typical updraft combustion and provides more ef~icient operation of the stove. The apparatus thus aids the burning of the volatile gases in several ways. First, by using horizontal combustion, the gases are forced to pass close to the hot coals which maintain sufficiently high temper-atures to ignitie them. In addition, the manually con-trolled inlet port 35, which is segregated from the primary air source, ;

't sb/l~, ~ 10~64~1 providcs air ~hicll is dl~c~ed clo~7n a path intcgral ~7i~h tlle heated l)ack wall and which is hecl~cd by ~he flue gases.
This channel preheats ~he air to maint:ain the air a~ the ;~
elevated tempera~ures required for secondary combustion Thus, oxygen from the secondary night inlet port 35 is directed~
into the secondary combustion chamber through numerous air ports to mix with the combustiblP gases and to provide secondary combustion. (During night operation when the ~ - , thermostat is turned down and damper 18 is closed, the ~;
secondary/night inlet port provides sufficient air to maintain a self-regulating cyclic operation.) In addition, behind the fireback which is provided at the back of the primary combustion chamber, the circuitous path consisting of passages 50, 52 conducts the smoke back and forth along the back of the apparatus and upwardly toward the exit at the flue collar 58. Since the heat o ;~
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 a higher temperature in the combustion chamber which aids in burning the volatile gases driven off from the wood. Thus, a large heat output is available~
In addition, the fire is controlled by not only the structure ~ ;
of the apparatus but by the thermostatically controlled `
input port 22 which supplies the primary air.
There is thus provided a wood-burning heating apparatus having an e~ceedingly high efficiency due both to its secondary combustion chamber and the secondary air supply supporting it, as well as t:o its long flue gas flow - 11 - ~,.
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~ 64~1 path and horizontal combustion.
Other embodi~)ents 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 (2)

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 baffle system 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, said baffle in combination with said frame member providing an opening connecting said primary and secondary combustion chambers for providing said gaseous communication therebetween, a primary air supply path for providing preheated air for promoting combustion in said primary combustion chamber, a pivoting side door, barrier means for providing a smokeless loading aperture in said frame member when said door is pivoted to an open condition, and a combustion products exit aperture at a top portion of said frame and in gaseous communication with said baffle system for providing an exit port for combustion products.

2. The apparatus of claim 1 wherein said barrier means comprises a vertical panel extending parallel to a side of said frame member between said primary chamber and a back wall of said frame member, and positioned adjacent said side having the door.