Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a hot air furnace that has a
firebox with an improved combustion air circulating system.
The improved firebox of this invention is especially suit-
ed for use with a furnace for heating room air in a situation where
it is mounted in the room to be heated although it is not intended
that the scope of the invention be restricted to such furnaces.
Furnace designs are legion. Basically, most of them were devices
to achieve the objectives of good capacity and good efficiency.
The purpose of this invention is to provide an improved firebox
whereby to achieve these objectives.
The furnace with a firebox of this invention achieves
good efficiency, good heating capacity for its size, and is economic
to build. It is unique in respect of the design of the combustion
air circulating system that it incorporates, a feature that gives
; it special advantage in achieving its objectives in use.
A furnace according to the invention comprises a firebox
for a furnace comprising a casing ha~Ting a combustion chamber with
an opening fox charging fuel; first inlet means from the combustion
chamber for a flue passage, said first inlet means being adjacent
the top of the combustion chamber; second inlet means from the com-
bustion chamber for a flue passage, said second inlet means being
disposed lower than said first inlet means; and suppl~ passage means
for combustion air to said combustion chamber having an~ntry open-
ing to said combustion chamber that is higher than said second in
let means for said flue passage. The invention will be clearly
understood after reference to the following detailed specification
read in conj~nction with the drawings.
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In the drawings:
Figure 1 is a view of a furnace showing the exterior
cabinet and the location of the firebox therein in broken lines;
Figure 2 is an illustration of the firebox, partly broken
away to show construction, with the cabinet in broken lines; and
Figure 3 is a view along the line 3-3 of Figure 1.
The furnace illustrated has an exterior cabinet 10 within
which is mounted a firehox 12. The general operation of the furnace
is similar to all furnaces of its general type. Air to be heated
is admitted to the space between the cabinet and the firebox;
becomes heated by reason of its heat exchange relation with the
firebox within which a fire is maintained; and leaves the space in
heated condition.
In the furnace illustrated air is admitted to the space
either through openings like cabinet opening 14 or through openings
like the grill openings 16. Openings like opening 14 are designed
for connection to a cold air pipe for conducting air tc be heated
from a more remote location. Openinqs like opening 16 take in
room air from the immediate area of the furnace. Heated air leaves
~0 the inter-cabinet firebox space through grill openings 18. No fan
forcing of the heated air is necessary in the embodiment of the
invention illustrated but it could be incorporated.
The circulation of air to be heated through a hot air
furnace is capable of wide variation and those versed in the art
will be able to vary the means shown. Further or more detailed
reference will not be made to it in this application because the
novelty o~ the invention resides in the firebox.
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The invention is more concerned with the circulation of
the combustion air and the design of the firebox 12 to achieve it.
The casing 12 is fabricated from stainless steel and has
a combustion chamber 20 to which combustion air is admitted through
air supply openings 22, and from which the gaseous products of com-
bustion are evacuated through a flue 24 that has a first inlet open-
ing 2~ and second inlet means comprising two openings 28.
~ ombustion air is admitted to chamber 20 through openings
22 by way of a series of baffles and ducts that preheat it prior
to admission. Air from underneath the cabinet travels through open-
ing 30 in the bottom of the cabinet and firebox; towards the front
of the firebox between the base plate of the firebox and baffle 32;
upwardly through openings 34 in baffle 30, towards the rear of the
firebox between baffle 32 and baffle 36 through openings 3~ in
baffle 36; towards the front and across the firebox betw~en baffle
36 and the firebox bottom to the inlets of vertical ducts 40;
across horizontal duct 42 ancl out openings 22 into the co~ustion
chamber~ When there is a fire malntained in the firebox the air
becomes preheated prior to its delivery to the combustion chamber
as it travels this path.
The location of the air entry port on the bottom of the
firebox and the extent of the tortuous preheating path is variable
and would be varied from model to model to achieve proper air entry
under operating conditions. These things are capable of variation
by a person skilled in the art.
The location of the flue inlets in the firebox is signif-
icant. Inlet 26 is at the top of the fire chamber and of itself
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is conventionally located. However/ it is combined with inlets
28 which are located below inlet 26 and below air inlets 22.
Flue 24 has a damper 44 operable within the flue by means
of a rotatable handle 46 that is journalled in link member 48. By
rotating the handle the damper can be operated between the open
position of Figure 1 and the closed position of Figure 2. The
handle can also be raised and lowered within the guide brackets 50
to cause the free end of link 52 to engage in slots 54 in the doors
56 to lock the doors in a closed position.
Doors 56 are hinged to a moulding around the door opening
of the cabinet as at 58.
The firebox will commonly burn wood and to load the fire-
box and ignite it one opens the doors, loads the firebox, sets
the dampers, lights the fire and closes the doors. In the begin-
ning one would adjust damper 44 fully open to get maximum draft
on fire start-up.
As the fire gains in intensity and the firebox becomes
hotter, damper 44 is closed gradually. On full fire it will, under
many draft conditions, be fully closed. As damper 44 is gradually
moved towards the closed position a ~reater percentage of the flue
gases leave through ducts 280 The combustion air enters the fire-
box through inlet 22, is burned in the firebox as it travels down-
wardly and the products of combustion leave through the ducts 28
the inlets to which are below the level of the air inlet 22. This
circulation of preheated air can be maintained and results in a
very efficient unit. The unit illustrated has a 30 inch firebox
and has a heating range of between 30,000 and 100,000 BTU's depend-
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ing on the fuel loading and damper operation. The highest ~ire
operation will be with damper 44 open because this would give maxi-
mum drat. The lowest fire operation would be with damper 44 closed.
The height of the ducts 28 from the bottom o~ the firebox
is variable Erom about 4 inches from the bottom to almost the top
o~ the firebo~ but it has been found that best efficiencies in the
30 inch fi~ebox illustrated are achieved when the height is about
6 inches from the bottom of the firebox. The top of the pile of
wood being burned is usually higher than the level of th~ bottom
of the duct openings 28.
The design of the combustion air supply passage will vary
and must have a resistance to flow that will provide for an adequate
supply of air to chamber 20 with the vent 26 closed to maintain
a low fire. The size from model to model will vary.
The firebox is illwstrated in a cabinet but it is contem-
plated that the firebox may be used without the cabinet. It could,
for example, be incorporated into the masonry of a fireplace either
with or without doors to the fire chamber.
The air to be heated in the embodiment illustrated is
supplied through opening 14 or openings 16 depending upon operation,
but in most cases it would not be supplied through ~oth openings.
In many cases air supplied through opening 14 would be supplied
through a duct leading from outside of the building. Thus, the
heated air in each case would be outside air. If openings 16 are
used for air to be heated, openings 14 would be closed and visa
versa.
Similarly, the combustion air that enters through the open-
ings 30 in the bottom of the firebox can be taken from the room
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or from outside of the building. It is preferable to take combus-
tion air from outside the building.
Embodiments of the invention other than the one illus-
trated will be apparent to those skilled in the art.
