Heat saving device

A heat saving device is provided for use in connection with the flue pipe of a stove, furnace, or similar heater. Instead of being exhausted directly into the atmosphere through the flue pipe, hot exhaust gases and other combustion products pass through a heat transfer chamber. An open-ended tube forms the inside wall of the chamber so that heat from the gases and other combustion products passing through the chamber is transferred to the useful air flowing through the tube. A removable shroud open at one end and baffled at the other partially surrounds the outer wall of the heat transfer chamber in spaced relationship to the outer wall, permitting flow of useful air through the space thus formed. The useful air flowing through this space is preheated by heat transferred through the outer wall and subsequently entrained by and mixed with air being blown through the inner tube by a fan. The total volume of useful air heated in this manner is added to the heated air provided by direct heating action of the heater. A two-bladed scraper mechanism is included for removing residue from the inner and outer walls of the chamber through which the combustion products pass.

BACKGROUND 
This invention relates to heat saving devices which are useful in 
connection with the flue pipe of a stove, furnace or similar heater. 
Such devices have been known for some time, as is evidenced by U.S. Pat. 
Nos. 1,785,649 and 2,147,658. Inventive activity in this field has been 
renewed with recent emphasis on energy conservation as is shown by U.S. 
Pat. No. 4,313,562. 
Devices of the type of the present invention function by scavenging the 
heat carried by exhaust gases and products of combustion, which normally 
pass through the flue pipe into the atmosphere. The heat accompanying the 
gases and combustion products would become wasted heat unless transferred 
to useful air. Useful air thus heated is then circulated into a room or 
space, adding substantially to the heat provided directly by the basic 
heater. 
It is obviously important that such devices deliver a large volume of 
heated useful air. This requires the efficient transfer of heat from the 
exhaust gases and combustion products to useful air. Also necessary is the 
smooth and relatively unobstructed flow of both useful air and the exhaust 
gases and products from which heat is extracted for transfer to the useful 
air. The invention provides a compact and efficient device meeting these 
objects. 
A single open-ended tube forms the inside of a chamber through which the 
hot exhaust gases and combustion products flow and provides for the smooth 
and unobstructed flow of a large volume of useful air in efficient heat 
transfer relationship with the hot exhaust gases and combustion products. 
The useful air is driven through the tube by a fan. Improved overall 
efficiency of heat transfer is attained by preheating some of the useful 
air flowing through the inside tube. This is made possible by a removable 
shroud positioned around the outside wall of the exhaust gas chamber in 
spaced relationship to the outside wall, leaving room for useful air to 
flow between the shroud and the outside wall of the chamber. Air flowing 
through this space is preheated and then is entrained and mixed with the 
useful air being blown directly into the inner tube. The resulting whole 
volume of useful heated air is added to the air directly heated by the 
stove or furnace. Importantly, means for cleaning residue from both the 
inside and outside walls of the exhaust gas chamber is included. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an efficient and compact heat 
saving device for use with the flue pipe of a stove, furnace, or the like 
heater, thereby conserving energy. This is accomplished by providing a 
unique structure for transfer of heat from the exhaust gases and 
combustion products in the flue pipe to useful air which is then 
circulated in the space to be heated. The invention comprises a chamber 
for smooth flow therethrough of gases and combustion products intended for 
exhaust from the heater to the outside atmosphere, as through a flue pipe. 
Suitable inlet and outlet openings for the gases and combustion products 
are provided in the outer wall or shell of the chamber. These openings are 
provided with sleeve-like pipe sections for mating with the flue pipe or, 
alternatively, a flange or other fitting formed on the heater itself. 
An open-ended tube forms the inside wall of the chamber. This tube is 
supported by the end walls of the exhaust gas chamber. As useful air is 
forced through the open-ended tube heat is transferred from the hot 
exhaust gases in the chamber to the useful air in the tube. 
A removable shroud is designed to partially surround the exhaust gas 
chamber in spaced relationship to the outer wall of the chamber. The 
shroud is open at one end to permit useful air to enter and flow through 
the space formed between the outer wall of the exhaust gas chamber and the 
shroud, thereby transferring heat from the exhaust gases to this useful 
air. 
The other end of the removable shroud has a baffled opening in line with 
the opening in the inner tube to direct movement of air into the tube 
opening. A second baffle, which is removable, is provided on the inside of 
the shroud spaced from the first baffle and close to the opening in the 
inner tube. A motor driven fan is mounted in an opening in the second 
baffle in position to force useful air through the opening in the inner 
tube. 
The combination of the second baffle and the fan serve to move useful air 
through the shroud and into the open-ended inner tube which forms the 
inside wall of the combustion products chamber. Useful air to be heated is 
drawn into the baffled end of the shroud more or less directly and forced 
through the inner tube. Additional useful air is also drawn into the open 
end of the section of the shroud which partially surrounds the outside 
wall of the exhaust gas chamber and is preheated by transfer of heat 
through said outside wall. After being diverted by the second baffle, this 
volume of preheated useful air is entrained by and mixed with the other 
volume of air being forced directly into the inner tube. Additional heat 
is thus transferred to this preheated useful air as the latter is moved 
through the open-ended tube and into the room or space to be heated. 
Another feature of the invention is the means for cleaning the residue of 
the combustion products from the inside walls of the exhaust gas chamber. 
For convenience and ease of operation the cleaning means comprises a 
scraper made in two arcuate sections which cooperate to clean the inside 
walls. Handles connected to the scrapers extend through the end walls of 
the chamber and are readily accessible for manipulation to remove residue 
deposited inside the chamber.

PREFERRED EMBODIMENT 
The preferred embodiment of the invention is described as it would be used 
with a free standing stove which is normally constructed of metal plate or 
sheet metal. Such a stove requires a flue pipe for venting smoke, gases, 
and other products to the atmosphere. In FIG. 1, the heat saver, generally 
indicated by reference numeral 10, is shown mounted on an outside wall of 
a stove H; in this case, the top surface of the stove is shown in dotted 
lines. FIG. 2 shows an opening V in the top surface provided with an 
upstanding flange or collar F which would normally receive the flue pipe P 
(all shown in dotted lines) for venting combustion products directly into 
the outside air. The heat saving device 10, which may be inserted in the 
flue pipe at any convenient point is shown in this case mounted directly 
on the stove's top surface. 
The heat saver 10 comprises a chamber 12 through which the combustion 
products, including smoke and hot exhaust gases, flow in the directions 
shown generally by arrows in FIGS. 2 and 3. The chamber 12 may be annular 
in shape and includes an outer wall 14 having oppositely disposed openings 
16 and 18. An open-ended inner tube 20 supported by end walls 22 and 24 of 
chamber 12 forms the inner wall of the chamber. 
The hot exhaust gases and other combustion products enter the chamber 12 
through opening 16 in one side of the chamber and exit through opening 18 
directly opposite the entrance opening after flowing around inner tube 20. 
A section of pipe or tube 26 is welded at one end to chamber wall 14 and 
fitted tightly to flange F at its other end, providing for unobstructed 
flow of exhaust gases from the opening V into the chamber 12. A second 
pipe section 28 is similarly attached to outer wall 14 at one end and has 
its other end inserted inside flue pipe P to permit flow from the exit 
opening 18 into the atmosphere. While not shown, it is assumed that a 
damper or other flow control device can be provided in flue pipe F. 
An open-ended shroud 30, in this case tubular in shape, partially surrounds 
the outside wall of the exhaust gas chamber 12. As best seen in FIG. 4, 
the outside diameter of outer chamber wall 14 is substantially smaller 
than the inside diameter of the shroud 30, providing an annularly shaped 
space 31 for unobstructed flow of air between the wall 14 and the section 
of the shroud 30 which surrounds the wall. 
Shroud 30, which is removable, has cut-out portions 32 and 34 which 
slidably receive and closely fit around exhaust gas inlet and outlet pipes 
26 and 28, respectively. Fasteners, such as screws 36, inserted through 
holes in the shroud 30 and into threaded holes in lugs 38 welded to pipes 
26 and 28, hold the shroud in position. The shroud 30 extends beyond the 
end wall 24 of exhaust gas chamber 12 and is provided with first and 
second baffles 40 and 42, respectively, for controlling and directing the 
movement of useful air, i.e., air to which heat scavenged from the hot 
exhaust gases is transferred. First baffle 40 is welded to the shroud and 
has a central opening 44 for admitting useful air into space or 
compartment 46. Second baffle 42, also provided with a central opening 48, 
in line with opening 44 in the first baffle, is removably mounted in the 
interior of shroud 30 in spaced relationship to first baffle 40, forming 
the other end of compartment or space 46. Screws 50, inserted through 
suitable holes spaced around the periphery of shroud 30 and into matching 
threaded holes in lugs 52 carried on second baffle 42, fasten the latter 
in place. 
An exhaust type fan 55, having appropriate air flow and power ratings, is 
mounted in opening 48 in second baffle 42. The fan 54 is mounted on baffle 
42 by attachment to brackets 56. With this arrangement, useful air will be 
drawn through opening 44 in first baffle 40 as well as the space 31 
between the outer chamber wall 14 and shroud 30, and after mixing in the 
compartment or space 60 between end wall 24 and baffle 42, will be forced 
through inner tube 20, as indicated by arrows in FIGS. 1 and 4. In the 
process, the volume of air flowing through space 31 will be preheated by 
transfer of heat from the hot exhaust gases through wall 14. After being 
diverted by baffle 42 and mixed or entrained with the other volume of air 
entering through openings 44 and 48, the resulting volume of air will 
receive additional heat as it is forced through inner tube 20 by transfer 
through the wall of the tube. The useful air with its temperature thus 
increased is recirculated into the space being heated, adding 
substantially to the amount of heat provided directly by the stove H. 
To maintain the heat exchanging efficiency of the device, a mechanism is 
provided for removing any residue collecting inside the combustion 
products chamber 12 comprising complementary arcuate scrapers 70 and 72 
positioned inside the chamber and arranged so that each scraper can be 
slid along the length of the chamber 12 in contact with the inside 
surfaces of the chamber walls. The scrapers may overlap slightly to ensure 
that the entire inside surface of both walls is covered. The scrapers are 
mounted to slide along guiding rods 71 and 73 welded to end wall 24 of 
chamber 12. Hollow tubular handles 74 and 78, which receive the rods, are 
attached to the scrapers. The handles pass through openings provided in 
end wall 22 of chamber 12. Hand grips 80 are provided on the scraper 
handles. 
It can be seen readily that the invention provides a compact, efficient 
structure for use as a heat saving device. The structure is also such that 
its parts can be readily made and assembled into a unitary device that is 
relatively easily installed for operation. In the construction of the 
device consideration has been given to the types of materials used; for 
example, a relatively heavy gauge metal may be the most satisfactory from 
the point of view of absorbing heat from the products of combustion for 
transfer to useful air. An additional advantage inherent in the structure 
is the cooling of the outside wall of the combustion products chamber and 
the flue pipe itself, and the distribution of the heat scavenged to other 
areas of the space, at some distance from the heater.