Note: Descriptions are shown in the official language in which they were submitted.
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HEATING APP~TUS ~I~VING IMP~OVE:D COMBUSTION
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The inventi~n relates generally to heatiny apparatus
and in particular to a wood-burning heating apparatus having
a high heat conversion efficiency.
BACKGROUND OF THE INVENTION
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Wood-burning s~oves have been available for centuries.
Perhaps the most well-known wood-burning stove is the Franklin
stove which, while being practical Eor 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.
~rhe 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 fixeplace is usually consumed
by the coals at the ~ase of the fire mass, causing the gases
to rise through an oxygen-deficient atmosphere. The loss of the
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 hothering to ignite it first. In addition, the
volatile gases given off from thR wood without being ignited
may also 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 sold creosote form, as a
chimney fire.
One effective method and apparatus for reducing the
volatiles is found in a horizontal combustion heating apparatus
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wherein the flames mov~ horizontally in -the primary combustion
zone. This is radically difEerent from typical updraft combus-
tion and is -the basis of the more efficient oper~tion of a
stove manufactured by Vermont Castings, Inc , the assignee of
this invention, which has been sold since at least the first
quarter of 1976 under the trade name "DEFIANT". The DEFIANT
parlor stove aids the burning of the volatile gases in several
ways. First, by using hori~ontal combustion, the g~ses are
forced to pass close to the hot coals which maintain sufficiently
high temperatures to ignite them. In addition, a manually con-
trolled secondary air source, which is segregated from primary
air source, provides air which 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 tempera-tures required for combustion. Thus, oxygen
from the secondary source is led into the secondary combustion
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chamber through numerous air ports to mix with the combustible ~.
gases and to provide secondary combustion. In the "DEFIANT", ;~;:
the secondary source of air is provided ;n the secondary com~
bustion chamber along an outside wall of th.e chamber, away from
the primary combustion chamber.
. In addition, behind the fireback which is provided
at the back oE the primary combus-tion chamber, a circuitous
path is provided by smoke baffles. The circuitous path is
comprised of a plurali-ty 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, signi~icant heat
transfer occurs from the flue gases to the surfaces of the
stove, which in turn is given o~f into the room rather than
being lost up the chimney. In addition, the circuitous
path aids in maintaining higher temperature in the com-
bustion 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 con-
trolled by not only the structure of the apparatus but by athermostatically controlled input port which supplies the
primary air.
Even though, the "DEFIANT" promotes secondary com-
bustion in the secondary combustion chamber, it is still
desirable to increase t~q 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 ob~ect of this
invention to provide a heating apparatus ha~ing 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.
A wood-burning apparatus according to the
invention features a heat-conducting frame member enclosing
a primary combustion chamber, a secondary combustion chamber
in gaseous communication with the primary combustion chamber~
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and a baffling arrangemerlt is gaseous communication with
the secondary combustion chamber for providi~g a long
internal flame pa-th. A vertically oriented downwardly
directed baEfle separates the primary and secondary com-
bustion chambers. A portion of the baffle is 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 combustion chamber. A secondary air supply
path extends at least along the downwardly directed baffle
for providing preheated air to the secondary combustion
chamber at said opening. A combustion product exit aperture
at a top portion of the frame and in gaseous communication
with the baffling arran~,ement, provides an exit port for
the combustion products.
In an illustrated embodiment of the invention there '~-
is featured a pivoting top cover for providing a smokeless
loading aperture in the frame top when the top cover is
pivoted to an open condition.
In another aspect of the invention there is featured
a rotatable flue collar for providing in one position a top
exiting heating apparatus and in a second position a rear
exiting heating apparatus. ''
In ,yet another aspect of the invention, a thermo-
statically controlled inlet port is provided in the frame
for supplying air to the primary and secondary supply paths.
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Dr SCRIP rloN o~i rHE;_ DR~WINGS
Other features, objects, and advantag~s of -the invention
will appear from 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 rear 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 4A is a cross-sectional schematic view of the
rotatable flue collar in the rear exit position according to
-the invention;
Figure 4B is a cross-sectional schematic view of the
rotatable flue collar in the top exit position according to
the invention;
Figure 5 is a cross-sectional view facing the back of
the fireback ~affle along lines 5-5 of Figure 3;
Figure 6 is a cros.s-sectional view taken along lines
6-6 of Figure 5;
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.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring to Figure 1, the wood-burning heating appar-
atus 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 o~ the frame
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member are joined to form an inte~ral air tight unit. The
front pivoting doors 12e, 12f, allow the heating ap~aratus
to be opened from the front for both loadiny of wood and for
viewing th~ fire when the heating apparatus is used as a fire-
place. A top cover 14 of the apparatus, has hinges 15a, 15b
which allow it to pivot to an upward position, whereby wood
may be loaded into a primary combustion chamber 16 (Figure 3)
through a smokeless loading aperture 17. The aperture size
is designed to sweep the opening clear of smoke when the top
cover is pivoted to an open condition. Preferably the ratio
of aperture cross-sectional area to the flue gas output exit
cross-sectional area is about three to one. Thus, even when the
stove is in operation, firewood may by reloaded merely by
dropping wood into the primary conbustion chamber. 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 prima`ry
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combustion chamber 16 through a primary inlet port 18 and a . : ~;
primary air supply flow path.20 (.Figure 3~. Inlet port 18 :
i5 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
oE bimetallic material connected to damper 22 by a flexible ;~ .
chain 24. Heatin~ apparatus 8 is also provlded with a damper ~`
control lever 25, a rotatable flue member 26, and a manually ~:
controlled night air inlet port 27 in side.memher 12a. :~
Referring to Figure 3, primary air extending through ~:.
aperture 23 travels through.primary air supply path 20 and is ~
heated by the fire which surrounds the tubes. Thus, the .
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primary a.ir is preheate~ and he:Lps to keep a hotter fire going
with less air and wood consumed. The primary combustion chamber
is bounded by the suhstantially vertically orien-ted downwardly
extending fireback baffle 28, the side walls 12a and 12b of
the frame member, the front doors 12e, 12f and ront wall 12c of
the frame member and the top 12h and bottom 12i frame member
panels.
A right-hand portion 29, of baffle 28 further provides,
a partial separation between the primary combustion chamber 16
and a secondary combustion chamber 30. The secondary combustion
chamber is connected to an is in gaseous communication with
the primary combustion chamber through an opening 31 in baffle ~:
28. A secondary air supply flow path 32 is provided, for the
secondary combustion chamber from thermostatically controlled
inlet port 18, and comprises an imperforate section 36 (.Figure
5) which extends from the inlet port 18 to substantially the
beginning of the secondary combustion chamber and a perforate
or apertured conduit 38 which extends with:in the secondary -:
combus-tion chamber along a bottom section of baffle 29. around
opening 31. The detailed nature of the secondary air supply is
described in more detail below.
There is further provided a third air supply path 40
which may be used -to provide air from manually controlled inlet ~;
27 to the secondar~ combustion chamber during night or other
selected periods of low heat output operation. Air supply
path 40 further provides additional oxygen for secondary
combustion in the secondary
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combustion chamber.
Behind the fireback baffle 28 are a pluraliky of
connecting smole passages 104, 106, 108 (E'igure 5~. These
passages direct the spen-t flue gases from the secondary
combustion chamber to -the left end o the apparatus, (looking
from the front), then into an upper channel or passage 41b
and back toward the right portion of the stove, and then
further up into an uppermost passage 41c and back toward the
left portion of the stove, where they finally exit through
the flue collar 26. The secondary combustion chamber, taken
together with the smoke passages, make up the flame path.
Since the heat of the flue gas 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 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 from the burning woodO .
. The heating apparatus, which is described above and
incorporates the pivoted top cover, is also disclosed and is
claimed in copending Divisional Application Serial NoO351,033,
filed May 1, 1~80. . .~.
Referring to Figures 4A and 4B, flue collar 26 is ~ - ;
preferably rotatable to allow operation of the apparatus with
either a horizontal exit (Figure 4A) or a vertical exit
~Flgure 4B) posltion. 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 collar
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is secu~ecl to -the inclinecl surEace 52 of the back portion by
two flue collar bol-ts 56 (only one of which is shown in the
figures). The two bolts are secured on opposed sides of -the
flue collar.
Referring to Figure 4A, an extended portion 60 of
the flue collar contac-ts vertically oriented sec-tion 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
180, the orientation shown in Figure 4B may be obtained. ~.
This orien-tation provides the top exiting stove and is main- :
tained by replacing the bolts 56. The extended portion 60
of the flue collar 26 is now positioned against the horizontally
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 enters .
through aperture 23 in frame back wall 12g and is almost ..
immediately divided between the primary and secondary flow :~:
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paths b~ 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 ~ireback baffle by an enclosing
member 72. Enclosing 72 not only directs the secondary air
flow toward opening 31 in baffle 28, but, in order to provide ~.
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a substantially uniform flow oE air into opening 31, the
cross-sectional area of the supply pa-th defined by enclosing
member 72 in combination with baf~le 28 increases substan-
tially as the path approaches the opening, as shown in 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 substan-
ially spaced apart parallel alignment with the baffle 28,
for example at 80 (Figure 3) so that the flow of secondary
air is substan ially unimpeded into the secondary chamber
at opening 31. The secondary air supplied at opening 31 i~
also preheated due to its proximity with baffle 28 so that
the efficiency of the secondary combustion chamber is increased.
That portion of the ambient air passing through
aperture 23 which follows primary flow path 20, passes ;~
through the baffle 28 near the lower base of the baf~le
(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
~low of combustion supporting oxygen across the entire depth
of the combustion chamber.
Thus the air provided by primary flow path 20 enters
the primary combustion chamber along the bottom left-hand
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surface of the ch~mber (lookiny ~rom -the front), and traverses
-the chamber tow~rd the right-hand side panel 12b, providing
combustion along the entire bot-tom o:E the wood supply. Upon
reaching the right-hand portion of the appara-tus, the air f low
is direc-ted toward and through opening 31 and exits through
-the circuitous flow path provided by the baEfle arrangement
extending between baffle 28 and rear wall 12g.
The heating apparatus, which is described above and
incorporates the slotted air tube conduit with a J-shaped
horizontall~ directed portion, is also described and is
claimed in copending Divisional application Serial No. 351,035,
filed May 1, 1980.
Referring to Figures 5 and 8, the baffle arrangement .
for directing the ~lue 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 baf~le 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 positionO Baffle 90 extends substantially from
side wall 12b to a position near side wall 12a. Baffle 92 `~
extends above ba~fle 90 and comprises a pair of tabular cast
supporting members 98, 100 which support a baffle plate 102
ex-tending substantially from side wall 12a to a position near
side wall 12b. The flue gases thereby are directed from a .,
:Eirst horizontally directed passage 104 to a second horizon-
tally directed passage 106 and then to a third horizontally
directed passage 108 from which they exi.t through flue collar
26.
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The heating apparatus is also provided with a damper ~ ~
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110 which enables the apparatus both to be used as a parlor
stove and as a firepl~ce. 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 generally indicated by arrow 114. ~his provides updraft
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 ~lue 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 12g
has a series of corrugations 122, 124, 126, which protrude
outwardly from the plane of back wall member 12g. These
corrugations provide additional heat radiation surfaces for
the heating apparatus for increasing the heat delivery to
the surrounding air; In addition, the corrugations provide
convenient means for channeling "night air" from the manually
controlled inlet port 27 to the secondary combustion chamber
through the night air flow path 40. Thus, the lowermost
corrugation 126 is blocked off by a plate 130 and is used to
channel the night air into or at least towards the secondary
combustion chamber.
The heating apparatus, which is described above and
incorporating the corrugation shaped back panel is also
described and is claimed in copending Divisional application
Serial No. 351,036, filed May 1, 1980.
In the preferred embodiment of the inven-tion, the
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opening 31 has a height of between 3 and 4 1/4 inches and is
preferably 4 inches high. ~t has been found for the particular
apparatus depicted in Figure 3, that the height of opening
31 is important ~nd a height substantially greater than 4
inches increases the heat output of the apparatus and also
its conversion efficiency.
The described apparatus, while design 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 b~ttom 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 pre-
ferred embodiment to a larger wood-burning heating apparatus
such as the "DEFIANT" referred to above, wherein the secondary
combustion chamber exists aLongside o~ and not behind the
primary combustion chamber.
Other embodiments of the invention, including
additions, subtractions, deletions, and other modifications
o~ the preferred embodiment of the invention will be obvious
to one skilled in the art and are within the scope of the
~ollowing claims.
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