CA1076443A - 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

The invention relates generally to heating apparatus and in particular to a wood-burning heating apparatus having a high heat conversion efficiency.
This is a division of copending Canadian Patent Application Serial No. 298,050, ~iled March 2, 1978.
T~ood~burning stoves have been available for centuries. Perhaps the most well-known wood-burning stove is the ~ranklin stove which, while being practical ;~
for its-rtime,~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 resons, 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 vo].atile ~ases is a serious i~
problem, because they represent approximately half of the total heat value of the wood. It is a though one were to ~un an open line of natural gas up a chimney without bothering to ignite it first. In addition, the volatile gases given off f~om the wood without being ignited may i condense on the cool sides of long metal flue pipes and ;~
drip out as creosote which may sometlmes 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 i~ o~e~d ~combustion efficiency.

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--` 10~6~3 Ye~ further vhjcc~s o.E the invelltioll arc-~ to provide a wood-blJrnincJ apparatus whieh .i.~ reliable, which is simple to opera~e, whi.ch is eapable of long-term operation with a single load o~ wood, whieh has a hi.gh heat output.
Aeeording to the present invention, there is provided a wood-burning heatiny apparatus including a heating eonducting frame member havi.ng a plurality of exterior pane:Ls assembled to enclose a primary eombustion ehamber, a secondary eombustion chamber in gaseous eommunica-tion with the primary combustion chamber, and a baffle system in gaseous communicatlon with the seeondary eombustion ehamber, for providing a long internal flame path. The panels being intereonnected along their edges with channeled construetion. A vertieally oriented, .:~
down~ardly direeted baffle is provided for separating the primary and seeondary combustion ehambers., the baffle in eombination wi.th the frame member providing an opening -~
eonneeting the primary and seeondary eombustion ehambers for the gaseous eommunieation therebetween. A primary air supply path i.s provided for preheating air for promoting eombustion in the primary comhustion ehamber, and a combustion products exit aperture is provided at a top portion of the frame and in gaseous eommunication with the baffle system for providing an exi-t port for ombustion . ~-products. :

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O~h~r fea~lres~ objec~s, and advan~ages of the inven~ion wil] appear frc~m thc~ ollowing description of a preferred em~odiment taken together with the drawings, in which:
Figure 1 is a fron~ perspective view of a heating apparatus according to the invention;
Fi.gure 2 is a baclc perspective view of the . ~:
heating apparatus of Figure l; . `~
Figure 3 i.s a cut--away front perspective view of the heating apparatus according to the invention;
Figure 4 is a cross-sectional view taken alon~ .
lines 4-4 of Figure 3; and Fig~re 5 is an enlarged view of the circled area of Figure 4.
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DESCRIPTION OF A PREFERRED EM~ODIMENT
General Description Referring to Figure 1, a 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 ~oined in a channeled construction to form an integral, air-tight unit. The front pivoting doors 12e, 12f, allow the heating apparatus to be opened from the front for both loading of wood and for viewing the fire when the heating apparatus ls used as a fireplace. A pivoting side door 14 of the apparatus, has hinges 15a, 15b which allow it to pivot about a vertical rotation axis, whereby wood may be loaded into a primary combustion chamber i6 (Figure 3) from the side of 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 tFigures 3 and 4) whose position is controlled 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. Illustrated top member 12h supports a cast iron cooking surface 21.
Referring to Figures 2 and 3, air isssupplied to the primary combustion chamber 16, through a primary inlet port 22, by a primary air supply flow path having branches 24a, 24b (Figures 3 and 4). Inlet por-t 22 is thermostatically controlledbby a thermostat covering an aperture 30 in the back frame member 12g. Thermostat 26 ~0'7tj~3 is for example an 8" coil oE bimetallic materlal connected 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 (Fgiure 3) through a secondary air flow path 37.
Referring to Figure 3, primary air entering through aperture 30 travels through primary air supply paths 21~a, 24b and is heat~d 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 baffle 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 frame member panels, and a vertically oriented interior panel 40 which separates the primary combustion chamber from the secondary combust~on chamber 36.
The secondary combustion chamber is connec-ted to and is in gaseous communication with the primary combustion chamber th~ough 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 frame members.
The secondary combustion chamber is bounded by the vertically oriented panel 40 in combination with frame members 12b, 12c, 12g, 12h, and 12i. As noted above, the secondary combustion chamber receives preheated air from the air inlet port 35 . .
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10'î ~3 through the secondary air supply flow path 37. The flow path 37 comprises an imperforate section 48 which extends between the inlet port 35 and panel 40, a~d 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 c rcuitous path from the secondary combustion chamber to the flue exit 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 flueecollar 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 frame.nmembers, 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 escaplng from the burning wood.
The illustrated flue collar 5~ is attached to the top panel 12h and provides a vertical or top exi-t for the spent flue gases. In othereembodiments 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 Elue gases.
-The Prim_ry Air ~low 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 immediately 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 of 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 holes 66 extending therethrough for providing preheated primary air to the back of the primary combustion chamber. Illustrated enclosing memb~r 64 i9 a cast iron plate and branch 24b has a substantially constant cross-sectional area along its length. ~ ~;
Tha-t 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 baffle (Figure 3) and is directed into the primary combustion chamber along a periodically slotted conduit 68 which extends from baffle -~
38, along side wall 12a tbelow 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 area which is substantially cons-tant and is partially open at end 70. Primary air is thus provided to promote a uniform flow of combustion supportingi~oxygen across the entire primary combustion chamber.

_7--107~443 The air provided by primary flow branches 24a and 24b thus enters the primary combustion chamber along the bottom back and bottom left-hand boundary surfaces of the chamber (looking from the front), and provides combustion along the entire bottom of the wood supply.
Upon reaching the right-hand portion of the primary combustion chamber, the air flow tnow containing volatiles) continues 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 baffle system 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 trans-verse 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 and 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).
Triangular plate 94 provides a barrier to prevent flue gases in the space behind the fireback from escaping through an opened side door.
The above-described heating apparatus having the baffle means for providing a smokeless loading is also described and is claimed in copending division application Serial No. 330,771, filed June 28, 1979.

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:10~ 43 The upper baEfle g2 extends above baffle 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 -~
fireplace 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 18 ensures that the flue is closed befoxe 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 engages 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 co-pending divisional application Serial No. 330,772, filed June 28, 1979.

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In an embodiment of the invention, the opening 44 has a height of between 3 and S inches and is preferably 4 1/2 inches high. It has been found for the particular apparatus depicted in Figure 3, that the height of opening 4~ is important and a he~ght sub_ stantially greater than 4 1/2 inches increases the heat output of the apparatus and also its conversion efficiency.
To further control combustion within the heating apparatus, the illustrated frame members of the present invention are interconnected along their edges in a channeled construction (Figure S). The channeled con-struction consists of a cast groove 130, at the edge 131 of one of the joining members, which receivesaa~ayer 132 of plastic sealing material, for example an asbestos gasketing material, and the other joining member 133.
This construction provides an airtight, physically secure and rigid structure.
Thus the present invention provides an effective ;-apparatus for reducing the volatiles found in typical updraft combusion 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 efficient 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 temperatures to ignite them. In addition, the manually controlled in~let port 35, wh~ch is segregated from the primary âir source, : ~
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provides air which is ducted down a path integral with the heated back wall and which is heated by the flue gases.
This channel preheats the air to maintain the air at the -elevated temperatures 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 combustible 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 op~ration).
In addition, behind the fireback which is provided at the back of the primary combustion chamber, the circuitous p~th 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 of the flue gases is considerable, significant hea-t 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 tempera-ture 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 w~ich supplies the primary air.
There is thus provided a wood-burning heating apparatus having an exceedingly h~g~ ePficiency due both to its secondary combustion chamber and the secondary air supply supporting it, as well as to its long flue gas flow --11-- , 1076~43 p~]l allcl llori.~.on~ l colnl~usl:ic)r O~:ller el~1bot'~ t ll~s of ~ e i.nven~:ion~ inc~.udirlg additiolls, subt:rac tions, de:l.eti.ons, and ot:her modificat:ions ~ .
of tl~e preerred embot]iment of t::he -inventiorl will be obvious to one skilled in ~he art and are wiLhin the scope of thé
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 heating conducting frame member having a plurality of exterior panels assembled to enclose 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, said panels being interconnected along their edges with channeled construction, 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, 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.