Heating furnace

A combination furnace including a solid fuel burning section and an electrically powered heating section. The two sections are disposed within an upright, insulated casing. A heat exchanger is provided above a fire box which constitutes the fuel-burning section. Dampers control the flow of combustion air to the fire box and the heat exchanger.

BACKGROUND OF THE INVENTION 
This invention relates to a furnace, and more particularly to a furnace 
which is usable in home heating. 
The particular furnace described herein is a combination furnace, in that 
it includes an electric heating section and a solid fuel, i.e., wood 
burning section. The electrically powered heating section and the fuel 
burning section may be installed with individual remote thermostats 
controlling heat output. The thermostat for the wood burning section may 
be set at the desired room temperature, with the thermostat for the 
electrically powered heating section at the minimum desired room 
temperature, a few degrees lower. With this type of installation, the 
electrically powered heating section then serves as a backup for the wood 
or fuel burning section. The arrangement also makes it possible to actuate 
both the wood burning section and the electrically powered heating section 
at the same time, by simply turning both thermostats to settings above 
room temperature. 
The furnace of the invention also features a construction wherein it may be 
mounted in a relatively confined space. As a consequence, the furnace is 
well adapted for mobile home installation, where, typically, space for 
mounting a furnace is limited. While well suited for mobile home 
installation, the furnace, of course, can be utilized for fulfilling other 
heating requirements. 
A feature of the furnace of the invention is the provision of a fire box 
having metallic, i.e., heat conductive walls, which forms the solid fuel 
combustion chamber in the furnace. Combustion products pass upwardly from 
this combustion chamber and thence through a metallic heat exchanger 
disposed above the fire box. From the heat exchanger the combustion 
products pass upwardly through a flue which connects with the usual 
chimney, exhausting to the atmosphere. Damper means is provided, including 
a fire draft damper which controls the admission of fresh air to the fire 
box, and a balance draft damper controlling the admission of fresh air to 
the heat exchanger disposed above the fire box. The dampers work 
oppositely to each other, which is to say that when one is opened the 
other is closed. Further explaining, when the room thermostat calls for 
heat, the balance draft damper controlling air flow to the heat exchanger 
closes and the fire draft damper controlling air flow to the combustion 
chamber opens, to increase the burning rate of fuel in the fire box and 
the heat given off by the fire box and the heat exchanger thereabove. On a 
given limit temperature being reached, the fire draft damper closes and 
the balance draft damper opens, which has the effect of reducing the 
burning rate of the fuel and allowing cool air to circulate through the 
upper heat exchanger and out the flue. This rapidly drops the temperature 
of the heat exchanger, and also has the effect of flushing out creosote 
and other residuals which might contribute to a fire hazard in the flue 
system. 
A blower, located adjacent the top of the furnace, when actuated, pulls air 
inwardly through a return air port located adjacent the top of the 
furnace, and forces such air downwardly through the furnace, first over an 
electrically powered heating section, and thence over the heat exchanger 
and fire box above-described. With no power delivered to the electrically 
powered heating section, such air is heated solely by the heat exchanger 
and the fire box. With fuel burning in the fire box, and with electric 
power delivered to the electrically powered heating section, such air is 
heated by both instrumentalities. The electrically powered heating 
section, heat exchanger and fire box are all mounted within an insulated, 
upstanding furnace casing functioning to channel air being heated 
downwardly through the furnace as such passes over the electrically 
powered heating section, heat exchanger and combustion chamber, finally to 
flow into a supply plenum for heated air located adjacent the base of the 
furnace. 
Objects of the invention, therefore, include the provision of a practical, 
solid fuel burning and electrically powered combination furnace for home 
heating applications; the provision in a furnace, with solid fuel burning 
capability, of a fire box forming the combustion chamber connecting with a 
secondary heat exchanger, and damper means including a fire draft damper 
and a balance draft damper effective to control burning rate and heat 
exchanger temperature; the provision of a furnace with an insulated casing 
forming the exterior of the furnace, adapting it for mounting in a 
confined space; and the provision of a furnace with solid fuel burning and 
electrically powered capability which may be manufactured as a factory 
built unit, and is relatively easily installed. 
These and other objects and advantages are attained by the invention, which 
will become more fully apparent from a reading of the following 
description, which is to be taken in conjunction with the accompanying 
drawings, wherein:

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
Referring to the drawings, a furnace constructed according to a specific 
embodiment of this invention is illustrated generally at 10. The furnace 
shown is adapted to be mounted in the space usually provided in a mobile 
home for the provision of a conventional furnace, such as a closet space. 
The furnace includes an upright, substantially rectangular casing 14 which 
is supported on floor 15 of the place where it is installed by 
non-combustible base 16. Frame panels 17, which may be hinged or 
removable, close off the front of the casing. Shown at 18, is a return air 
opening which may be provided with a trim grill 19 through which cool air 
from adjacent the top of the space being heated returns to the furnace for 
heating purposes. Air passing downwardly through the furnace and heated by 
such passage travels downwardly through the base of the furnace, through 
opening 22, into a heated air supply plenum 24 from which the air is 
channeled to the desired locations in the space being heated. Outside air 
to support combustion, referred to as "combustion air", enters the furnace 
through combustion air inlet 26. 
Casing 14 over the interior thereof is completely insulated, as with 
one-inch thick, foil backed, fiberglass duct board 28. This insulation 
enables the furnace to be mounted in a relatively confined space with 
minimal clearance between the outside of the casing and the walls of the 
space. 
Mounted within the furnace casing adjacent the base thereof and on the 
non-combustible base is a fire box 30. The firebox, which defines within 
it a combustion chamber for fuel, is substantially rectangular in shape, 
with sides, top and back in thermal communication with air moving 
downwardly through the interior of the furnace. A hinged fire box door 32, 
when opened, exposes an opening for the introduction of solid fuel into 
the fire box. 
Interior of details of the fire box are more or less conventional. Such may 
include the usual cast iron grate 33 spaced above an ash pit adjacent the 
bottom of the fire box. If desired, a metal drawer 36 may be provided in 
the ash pit below the grate as a convenient method for removing ash 
accumulation. Door 31, when opened, exposes an opening providing access to 
the ash pit. The fire box (and internal structure) being made of metal, 
has heat conductive walls, and thus functions as a heat exchanger, 
exchanging heat from the fuel combusting within the combustion chamber 
defined by the box to air travelling over the exterior of the fire box. 
Disposed above the fire box, and suitably supported in spaced relation over 
the top of the box, is a heat exchanger 34 of substantially rectangular 
configuration. The heat exchanger has metallic side, top and bottom walls 
defining an enclosed space within the exchanger. A fire box collar 37 
connects an opening in the top of the fire box with another opening in the 
bottom of the heat exchanger. In this way, gaseous and gas-borne 
combustion products produced with burning of fuel in the fire box travel 
upwardly from the fire box into the heat exchanger. 
Connecting with an opening in the top of the heat exchanger, adjacent the 
other end of the exchanger from collar 36, is a flue 38. Such extends 
upwardly in the furnace past the return air opening 18 to a connection 
with a chimney 40. The chimney, although such is not shown, extends in the 
usual manner to an elevated position above the roof of the mobile home. 
The flue and chimney provide a passage for gaseous combustion products 
leaving the heat exchanger upwardly through the furnace and thence to the 
exterior of the home whence such products are expelled to the atmosphere. 
Combustion air inlet 26 connects with a duct system 42. Such includes an 
upstanding leg 44, and connecting with this upstanding leg, laterally 
outwardly projecting legs 46, 48. Lower leg 48 connects through an opening 
50 to the interior of the fire box. Upper leg 46 connects to an opening 52 
with the interior of the manifold. 
Controlling air flow from leg 44 into leg 48 is a fire draft damper 54. 
Controlling flow of air from leg 44 into leg 46 is a balance draft damper 
56. Each damper comprises a plate, which in an upstanding position closes 
off the leg with which the damper is associated. The plate is pivotable 
about its lower margin to a horizontal position, wherein the leg with 
which the damper is associated is fully open. 
A damper motor housed within a housing is shown at 58, having an output 
shaft means connected to a pair of arms 60, 62, such arms being 
link-connected through links 64, 66 to the fire draft damper and balance 
draft dampers, respectively. With movement of the arms upwardly in FIG. 1, 
the balance draft damper, which is shown in an open position, swings to a 
closed position, and the fire draft damper, which is shown in a closed 
position, swings to an open position. Return movement of the arms by 
movement downwardly returns the dampers to the positions shown. In this 
way, the two dampers are oppositely connected, with one moving to an open 
position while the other moves to a closed position, and visa versa. 
Indicated generally at 68, and disposed above heat exchanger 34, is an 
electrically powered heating section. This may include the usual 
electrical coils 69 housed within a housing 70 which defines a path for 
moving air downwardly over the coils and thence out the base of the 
section onto heat exchanger 34. Such movement of air is produced through 
actuation of a blower generally shown at 72, which may include the usual 
electrically driven squirrel cage blower, operable to pull air inwardly 
through the inlets thereof and thence to force such air downwardly through 
heating section 68. 
The damper motor may be provided with a spring-based mechanism operable to 
move the fire draft damper to a closed position and the balance draft 
damper to an open position with de-energizing of the motor occurring as a 
result of power failure. The electrically powered heating section and the 
solid fuel burning section may be controlled, as by a pair of thermostats, 
one of which may control the fuel burning section, and the other of which 
may control the electrically powered heating section. Normally, the 
thermostat for the fuel burning section is set at the desired room 
temperature, and the thermostat for the electrically powered heating 
section is set at the minimum desired room temperature, a few degrees 
lower. In this way, the electric section then serves as a backup for the 
wood section. 
A control means operated by the thermostats is selected whereby when the 
remote thermostat for the solid fuel-burning section calls for heat, the 
damper motor is energized and opens up the fire draft damper, and closes 
the balance damper. This causes outside combustion air to be admitted to 
the fuel burning section and shuts off the flow of such air through the 
upper heat exchanger. When the temperature in the area surrounding the 
heat exchanger reaches a setting in the control system set for causing the 
fan or blower to come on, such as 140.degree. F., the blower is activated, 
and air is caused to be circulated downwardly in the furnace over the fuel 
burning section to be delivered to supply plenum 24. On the remote 
thermostat controlling the wood section being satisfied, a signal is 
produced causing the damper motor to de-energize, which returns the fire 
draft control to the closed position and opens up the balance draft 
damper. This reduces burning rate of the fuel in the combustion chamber 
and allows cool air to circulate through the upper heat exchanger and out 
the flue, which rapidly drops the temperature in heat exchanger 34. The 
fan continues to run until a lower setting in the control means is 
reached, normally about 90.degree. F. 
When the temperature in the area surrounding heat exchanger 34 reaches an 
upper maximum, for instance, 175.degree. F., the fan limit control closes 
the fire draft damper and opens the balance draft damper, even if the 
remote thermostat is calling for heat. The fire draft damper will stay 
closed until the heat exchanger area temperature drops below 175.degree. 
F. The fan will continue to run to induce cooling temperature. 
The furnace may also be equipped with an auxiliary temperature limit switch 
located in the fan compartment, which de-energizes the damper motor 
causing the fire draft damper to close and the balance damper to open if 
the fan compartment temperature reaches a certain level, for instance, 
160.degree. F. Excessive temperatures in the fan compartment indicate a 
fan motor failure, fan limit control failure, or a restricted duct. 
If it is desired to actuate both the fuel burning section and the 
electrically powered heating section at the same time, this is 
accomplished by simply turning both thermostats up above room temperature. 
While a specific control system for the furnace has been described, 
obviously variations in the control system are possible. Whatever the 
control system is utilized, the furnace has the flexibility, as the result 
of including both a fuel burning section and an electrically powered 
heating section, to supply the heating demands of the user using wood if 
such is available, both electricity and wood under extreme conditions, and 
using the electrically operated heating section, exclusively, at such 
times as when the fuel burning section is not operable. 
The insulated furnace casing confines the air moving downwardly through the 
unit during heating. Temperatures on outer wall surfaces of the furnace 
are maintained low enough to enable the furnace to be installed in a 
confined space, with minimal clearance between the furnace and outstanding 
walls. 
While a particular embodiment of the invention has been described, it 
should be obvious that variations and modifications are possible without 
departing from the invention.