CA2692384A1

CA2692384A1 - Variable combustion air control for wood stove

Info

Publication number: CA2692384A1
Application number: CA2692384A
Authority: CA
Inventors: Timothy C. Meints
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-10
Filing date: 2010-02-10
Publication date: 2011-08-10
Anticipated expiration: 2030-02-10
Also published as: CA2692384C

Abstract

The invention provides an improved control of the combustion air to a wood stove. The current operating temperature of a wood stove is obtained from the temperature of the flue pipe of a wood stove and is used to control the air intake of that wood stove. A
temperature monitoring housing, enclosing a bi-metal coil, is clamped to the wood stove flue pipe. The bi-metal coil is connected to a shaft which controls a lever.
This lever connects to a lever on the the air valve control housing. The air valve control housing bolts to the air intake the wood stove. This lever controls the position of an air valve internal to the air control housing and controls the volume of air to the wood stove combustion chamber. A offset control lever on the temperature monitoring housing allows the operating temperature of the wood stove to be set.

Description

Variable Combustion Air Control For Wood Stove, therefore The invention provides for a universal retrofittable automatic combustion air controller and improved control of the combustion air to a wood stove.

This invention provides an improved combustion air control for wood stoves and other combustable heaters such as pellet stoves that require an easily retrofittable combustion air control that does not void manufacturers warranties or government approvals, or can be incorporated into original heater manufacture.

Background of the Invention Combustable heaters such as wood and pellet stoves have been in existence for many years and have utilized many different methods of controlling the combustion air intake.
Typical combustion air controls, for example, in the following patents;

Canadian Patent Documents CA 1199542 Arsenault CA 1132024 Erickson CA 1158122 Paradis U.S. Patent Documents 4,409,956 Barnett 4,117,824 McIntire, McIntire It is common for wood stoves to have an adjustable combustion air inlet control for the purpose of adjusting the rate of combustion in the wood stove. These combustion air controls can be manually operated or automatic. The problem with manual controls is that the operator seldom has accurate feedback of the combustion temperature, and in any case, is seldom able to monitor the wood stove operation 100% of the time.
This results in an arbitrary setting of the combustion air which rarely matches the optimum setting. This optimum setting constantly changes from the beginning of the combustion process to the end of the combustion process, and may include the dynamics of fuel being added at any time during the process. Two main objectives regarding the burning of wood or pellets is the length of burn or the efficiency of burn. The length of burn objective is driven by the objective to have hot coals in the morning after an overnight burn. This simplifies the continuation of the burn by adding more fuel. The efficiency of burn objective relates to getting the maximum energy in the fuel transferred to the medium to be heated, whether that is air or water. This objective is desirable from the standpoint of economy in that the most amount of heat is obtained from a given amount of fuel. Both of these objectives have different optimum combustion air settings and these settings change from the start of the combustion process to the end. Attempts have been made to automate this dynamic process by adding temperature sensing mechanical and/or electrical sensors to the body of the wood stove and use these temperature inputs to control the combustion air inlet to the wood stove. The problem with these automated systems is that they take the temperature from the body of the wood stove which has a high thermal mass. It is actually the combustion temperature that is important in determining the optimum air setting. The combustion temperature can change rapidly but because of the thermal mass of the body of the wood stove, there is a delay between a change in the combustion temperature and a change in the temperature of the body of the wood stove. All temperature control apparatus that use the body of the wood stove to sense the combustion temperature will have a built in delay which will result in a delay in the opening or closing of the combustion air control. This air control delay will result in undesirable temperature swings in the combustion temperature. Any time that the combustion temperature is not at the optimum for length of burn, or for efficiency of burn, will result poor performance.
There are also a large number of wood stoves that only have manual controls, and therefore suffer from the limitations of manually controlled combustion air intake. In most cases the manufacturer did not offer an automatic combustion air control, or the buyer did not elect to purchase one if it was offered. The problem with adding an automatic combustion air control to these existing manual control stoves is that there is no automatic combustion air control of universal design in existence that is easily adapted to the various designs of wood stoves. Another limitation is that typical prior art automatic combustion air controls are based on sensing the temperature of the body of the wood stove, and therefore suffer from the combustion temperature swings that result from obtaining the control temperature from the high thermal mass of the wood stove body. An additional drawback to prior art automatic combustion air designs is that they are an integral part of the construction of the body of the wood stove, and can not be retrofitted to an existing manual wood stove without cutting or modifying the body of the manual wood stove and would then void the manufacturers warranty and governing bodies' approvals.
Another disadvantage to some prior art is that that they rely on electrical power to operate. For some customers of wood stoves the attraction is that the wood stove would provide heat even if the power went out, or they normally have no power. Those designs that rely on electrical power to operate would revert to manual control in the event of a power failure, or become inoperative.

Summary of the Invention I have found that these disadvantages can be overcome by controlling a combustion air inlet valve using the temperature of the stove's exhaust flue where it exits the wood stove.
As it is the combustion temperature we are the most interested in, the flue pipe close to where it exits the wood stove gives the closest proximity to the combustion exhaust gases.
Also the flue pipe is made from thin sheet metal and therefore has a low thermal mass. The flue pipe will react rapidly to flue gas temperature changes, and therefore react rapidly to combustion temperature changes. By designing a mechanism to react to the flue pipe temperature, and translate that change of temperature to a mechanical movement that controls the combustion air inlet, I am able to provide a combustion air inlet control that is more accurate and efficient than controls that rely on temperature inputs from wood stove bodies. In addition, as wood stove flues are of standard sizes, this design can be offered in standard sizes. In addition the flue temperature sensing unit clamps to the flue pipe, therefore no holes or modifications are required. A second assembly that works in conjunction with the flue temperature sensing unit is the combustion air control unit, it attaches over the wood stove's existing air intake, and does not require modification of the original stove design. The combustion air control unit is comprised of two concentric tubes, and outer tube and an inner tube with butterfly valve. The inner tube and butterfly valve diameter are sized for the size of wood stove it is to be used with, the larger the heating capacity of the wood stove the larger the diameter of the inner tube and butterfly valve. The outer tube is sized to fit standard air ducting sizes. Various countries use different standard fresh air duct sizes and the outer diameter tube can be selected to match the standard fresh air duct size of the country in which it is to be sold. The outer tube can be changed without affecting the optimum design inner tube and butterfly diameter. The action of the flue temperature sensing unit is connected to the combustion air control unit by a light chain. The length of the flue temperature sensing unit and the combustion air control unit can both be changed so the connecting chain clears obstructions on the wood stove body without changing the nature of the design or operation of both units.

An integral part of this design is the ability to connect a fresh air duct to the combustion air control. Many jurisdictions now require that the air wood stoves burn be sourced from a fresh air supply obtained from outside the building. This is so the stove does not consume the air from inside the building which can result in lower oxygen levels, a negative air pressure in the house and drafts. Also if the wood stove combustion air inlet is open to the inside air of the building there is the chance of smoke, embers and combustion gases from entering the house due to a sudden high pressure outside the building in relation to the inside of the building as could happen in the event of a strong wind or a ventilation fan inside of the building. The majority of prior art do not have the ability to effectively attach a fresh air duct.

An integral part of the nature of this invention is that various dimensions can be changed to allow it to be connected to various wood stove designs without reducing the effectiveness of the operation of the combustion air control. As there are various flue diameters, various flue clamp size diameters can be offered. In addition there can be different distances between the edge of the stove and the center of the flue pipe. This can be accommodated by varying the length of the flue temperature sensing unit. Stoves with different heating capabilities require different volumes of combustion air, the inner tube and butterfly valve can be resized to provide optimum air control at the rated air flow range. For example, a smaller stove with a smaller heat capacity will have a smaller combustion air requirement and therefore a smaller inner tube and butterfly valve, as compared to a stove of a larger heat capacity. It is important to correctly size the butterfly valve and inner tube to match the combustion air flow range of the stove. The combustion air intake of the stove can be offset from the side of the stove by various dimensions depending on the manufacturer of the stove. This can be accommodated by varying the length of the combustion air control unit.

In addition where the centerline of the flue is offset from the centerline of the stove's combustion air inlet, alignment can be accomplished by rotating the flue temperature sensing unit until the mechanical output of the flue temperature sensing unit lines up with the input of the combustion air control unit and clamping the flue temperature sensing unit in that position.

By stocking a small variety of lengths of flue temperature sensing units and combustion air control units, flue temperature sensing units with various standard diameter flue clamps, combustion air control units with various butterfly valve sizes and outer tube diameters, one can pick a combination that would fit almost any wood stove. For new stove manufacturers the design is an improvement over prior art in that the new stove could be purchased with the variable combustion air control system installed, or the air control system could be offered as an option that a customer could purchase and install at a later date.

For the purpose of illustrating the invention, there are shown in the drawings several embodiments which are presently preferred; it is to be understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown. In the drawings, which form a part of this specification, Fig. 1 is a diagrammatic view of a variable combustion air control system according to one embodiment of the invention, showing the flue temperature sensing unit clamped to the flue, the combustion air control unit mounted to a wood stove combustion air inlet, a fresh air supply source and a disconnected flexible fresh air connection duct.

Fig. 2 is a diagrammatic view of the flue temperature sensing unit portion of the invention, with the flue clamp separated into it's two parts, one part integral with the temperature sensor, the other part integral with the thermometer.

Fig. 3 is a sectional view of one half of the flue clamp that is integral with the flue temperature sensor of Fig 2, as seen from section line 3-3 of Fig. 2.

Fig. 4 is a sectional view of one half of the flue clamp that is integral with the thermometer of Fig. 2, as seen from section line 4-4 of Fig. 2.

Fig. 5 is a side elevational view of one half of the flue clamp that is integral with the thermometer of Fig. 2, as seen from section line 5-5 of Fig. 4.

Fig. 6 is a sectional view of one half of the flue clamp that is integral with the thermometer of Fig. 2, as seen from section line 6-6 of Fig. 5.

Fig. 7 is a sectional view of both flue clamps connected together showing the hole and ball retaining system of Fig 2, as seen from section line 7-7 of Fig. 5.

Fig. 8 is a sectional view of both flue clamps connected together showing the clamping system of Fig. 2, as seen from section line 8-8 of Fig. 5.

Fig. 9 is a diagrammatic view of the combustion air control unit portion of the invention.
Fig. 10 is a sectional view of the combustion air control unit of Fig. 9, as seen from section line 10-10 of Fig. 9.

Fig. 11 is a sectional view of the combustion air control unit of Fig. 9, as seen from section line 11-11 of Fig. 10.

Detailed Description of the Invention In the particularly advantageous embodiment of the invention illustrated , FIG. 1 shows the invention installed on a typical wood stove 3. The invention consists of a flue temperature sensing unit 1, a combustion air control unit 2 and an interconnecting light chain 81, collectively known as the Variable Combustion Air Control. The flue temperature sensing unit 1 has a two part clamping ring that clamps to the flue pipe 4 of the stove 3. The combustion air control unit 2 attaches over the combustion air intake opening in the wall 71 of the stove 3. The combustion air control unit 2 will accept a flexible fresh air duct 6 which in turn can be connected to the building fresh air inlet 5. Fresh combustion air from outside the building is admitted through the flexible fresh air duct 6 to the combustion air control unit 2 where it is metered to the combustion air inlet of the stove 3. The combustion temperature of the stove 3 is sensed by the flue temperature sensing unit 1 which is clamped to the flue pipe 4. As the combustion temperature increases so does the temperature of the flue pipe 4. As the temperature increases lever 35 rotates, which lowers the light chain 81. The light chain 81 is connected to lever 70 of the combustion air control unit 2, as the light chain 81 lowers the lever 70 rotates and begins to restrict the air flow through the combustion air control unit 2, thereby reducing the combustion temperature. By rotating handle 31 various temperature set points can be selected. If the combustion temperature decreases from the temperature set point then the process reverses and increases the air flow to the combustion chamber and therefore increases the temperature.
In FIG. 2 the flue temperature sensing unit 1 is shown with the flue clamping ring separated into it's two parts, the male clamp ring 37 and the female clamp ring 42.
These two clamping rings encircle the flue pipe 4 and provide the mechanical clamping action to maintain the flue temperature sensing unit 1 on the desired position on the flue pipe 4. The male clamp ring 37 and the female clamp ring 42 are connected together by a ball 55 and hole 40 arrangement as shown in detail in FIG. 7, and a male ball clamp 38, female ball clamp 39 and bolt 41 arrangement as shown in detail in FIG. 8. The hole 40 in the female clamp ring 42 is slightly larger than the diameter of the ball 55 which allows the ball 55 to pass through the hole 40 of the female clamp ring 42. The ball 55 is secured to the male clamp ring 37 by screw 56. The female clamp ring 42 overlaps and is positioned to the outside of the male clamp ring 37. The male clamp ring 37 and the female clamp ring 42 are prevented from sliding apart by the backside of the hole 40 in female clamp ring 42 wedging against the ball 55. The male ball clamp 38 is attached to the male clamp ring 37 by screw 79, female ball clamp 39 is attached to the female clamp ring 42 by screw 80.
The female clamp ring 42 overlaps and is positioned to the outside of the male clamp ring 37. A bolt 41 passes through the female ball clamp 39 and is threaded into the male ball clamp 38. As the bolt 41 is tightened it draws the female clamp ring 42 and male clamp ring 37 together, reducing the diameter of the circumference the two said rings, and thus clamping the flue temperature unit 1 to the flue pipe 4. There are four ball 55 and hole 40 arrangements and a male ball clamp 38, female ball clamp 39 and bolt 41 arrangements to evenly distribute the clamping pressure to the male clamp ring 37 and the female clamp ring 42.

In the embodiment shown in FIGS. 1-3 the tube 36 is attached to the male clamp ring 37, the male clamp ring 37 has an opening equal to the cross sectional area of the tube 36 and is concentric with the centre of the tube 36. This allows the interior of the tube 36 to be exposed to the radiating surface of the flue pipe 4. The interior of the tube 36 has a reflective surface to reflect and contain the radiated heat from the surface of the flue pipe 4 inside the tube 36.

The outer race 33 is a tight fit inside the tube 36 and is fixed in position.
The inner race 32 is free to rotate inside the outer race 33 and is held in position in relation to the outer race 33 by ball bearings 49, of which there are sufficient ball bearings 49 to fill the bearing race described by the radial grooves cut into the inner race 32 and the outer race 33. A hole, slightly larger in diameter than the ball bearing 49, is drilled into the top of the outer race 33 so the ball bearings can be loaded into the race before the inner race 32 and the outer race 33 are inserted into the tube 36. A plug 50 is inserted into the hole to provide the correct clearance for the ball bearings 49 in the race and to prevent them from jumping up and jamming the rotation of the mechanism. Another hole is drilled into the top of the outer race 33 to receive a spring 47. This spring pushes on a ball bearing 48 that will engage indents in the outer circumference of the inner race 32. These indents are evenly spaced for a distance of 120 degrees around the circumference of the inner race 32. A
threaded hole is drilled in the bottom of the outer race 33 and a threaded pin is installed before the assembly is inserted into the tube 36. This threaded pin engages a slot cut in a 120 degree radius around the outer circumference of the inner race 32. The spacing and position of the slot is such that the 120 degrees of rotation that the slot and threaded pin 54 allows the inner race 32 to travel coincides with the 120 degrees of evenly spaced indents that ball bearing 48 engages. The slot and indents are arranged in such a way on the inner race 32 that when the handle 31 is in the vertical position the slot and indents are at the beginning of their travel, and when the handle 31 is rotated 120 degrees from vertical the slot and indents have reached the end of their travel. Due to the universal nature of this design, changing the amount of travel of the handle 31 and the start and stop angle of the handle 31 in relation to vertical can easily be accomplished by simply changing the slot and indents dimensions on the inner race 32.

The perforated inner tube 65 is fixed to, and turns with, the inner race 32. A
bushing 30 is a tight fit in, and turns with, the perforated inner tube 65. A handle 31 is fixed to, and turns with, the perforated inner tube 65 and bushing 30. A shaft 34 is inserted into the bushing 30 and is free to rotate and move longitudinally independently of the bushing 30.
To the outside end of the shaft 34 a lever 35 is clamped using a set screw 46. The lever 35 is free to be clamped in any position longitudinally or radially on the shaft 34. One end of a spiral bi-metal coil 51 is clamped to the interior end of the shaft 34 using screw 53. The other end of the spiral bi-metal coil is clamped to the interior end of the perforated inner tube 65. The desired rotation angle of shaft 34 can be clockwise or counterclockwise by selecting a spiral bi-metal coil 51 that is either wound clockwise or counter clockwise.
The operation is such that when the stove 3 is initially cold but a fire has been started, is beginning to heat up, heat energy begins to radiate from the flue pipe 4. That energy is transferred to the spiral bi-metal coil by radiation, conduction and convection. Radiation energy not directed to the spiral bi-metal coil 51 is reflected back towards to the spiral bi-metal coil 51 by the reflective coating on the interior of the tube 36. The perforated inner tube 65 is only perforated for a distance that corresponds to the length of the spiral bi-metal coil 51. The perforations are the maximum that will still allow for the torsional rigidity needed by the perforated inner tube 65 to support the spiral bi-metal coil 51. These maximum perforations allow for the maximum energy transfer from the flue pipe 4 to the spiral bi-metal coil 51. As the spiral bi-metal coil 51 heats up it begins to rotate, this rotation is translated to the shaft 34 which is then translated to the lever 35.

The light chain 81 is connected to lever 35 of the flue temperature sensing unit 1 and lever 70 of the combustion air control unit 2 and translates the control information through the light chain 81 to lever 70 of the combustion air control unit 2.

In the embodiment shown in FIGS. 1 and 9-11, the combustion air control unit 2 controls the amount of air to the combustion chamber of the wood stove 3. The lever 70 receives the air control information and translates it to shaft 69. Shaft 69 passes through two holes in control outer tube 66 and two holes in control inner tube 67 in such a way that the shaft 69 bisects both tubes. A disk 74 is attached to the shaft 69 with three screws 76. The disk 74 is machined in an shape such that when the disk 74 is rotated to a position that the disk 74 would block the passageway through control inner tube 67, the perimeter of disk 74 would make contact with the inner diameter of the inner control tube 67. The perimeter of the disk 74 would make contact with the inner diameter of control inner tube 67 twenty degrees before the disk reached a perpendicular angle to the inner wall of the control inner tube 67. This prevents the disk 74 from jamming in the control inner tube 67.
In this position air movement is stopped from passing through the control inner tube 67. Rotating the shaft 69 in the opposite direction until the disk is perpendicular to the inner wall of the control inner tube 67 would allow the maximum air flow through the control inner tube 67.
A pin 82 projecting through the wall of the control inner tube 67 provides a stop to prevent the disk 74 from opening past the maximum open position. The diameter of the disk 74 and the control inner tube 67 can be varied to match the characteristics of the air control to the combustion air requirements of the particular wood stove it is to be used with. The control outer tube 66 attaches to the flange 68, the flange has a hole that is the same size, and concentric with, the inner wall of the outer control tube 66. The flange bolts to the stove air intake wall 71, covering the original air intake to the wood stove 3, and forcing all inlet combustion air to the wood stove 3 to pass through the combustion air control 2. The flange 68 is attached to the stove air intake wall 71 using four screws 72.
The outside diameter of the control outer tube 66 is selected to match the inside diameter of the flexible fresh air duct 6 used in the jurisdiction that the wood stove 3 is to be used.
The flexible fresh air duct 6 slips over the end of the control outer tube 66 that is opposite the flange 68 end, and is typically clamped in position using a stainless steel hose clamp.
The bulkhead 77 is attached to the control outer tube 66 and the control inner tube 67 and insures that all combustion air entering the wood stove 3 passes through the control inner tube 67.
Various chain connection points along lever 35 and lever 70 allow the rate at which temperature control information is transferred to be changed. In addition the transfer of temperature control information can be made non linear by repositioning lever 35 and lever 70 on their respective shafts and locking them in position using their respective set screw 46 and set screw 78. For example it may be desirable to have the butterfly valve open and close rapidly and widely about the set temperature point, or oppositely, have the butterfly valve open and close slowly and narrowly about the set temperature point. A
separate combination would have the butterfly valve open and close rapidly and narrowly about the set temperature point, or open and close slowly and widely. By changing where the light chain 81 attaches to lever 35 and lever 70 in combination with repositioning lever 35 and lever 70 on their respective shafts, any action of air control can be generated to match the individual characteristics of the various wood stoves 3 the Variable Combustion Air Control may be fitted to.

In the embodiment shown in FIGS. 1,2 and 4-6, the thermometer shown provides feedback to the operator of the flue gas temperature and can therefore infer the combustion temperature of the wood stove 3. This allows the operator to accurately position the handle 31 of the flue temperature sensing unit 1 to obtain the desired performance from the wood stove 3. For the same reasons that this position on the flue pipe 4 is the best place for the flue temperature sensing unit 1, it is also the best place to take temperature readings to determine the performance of the combustion process in the wood stove 3. I therefore use the other half of the flue clamp, the female clamp ring 42 to house the thermometer. The thermometer body 43 is attached to the female clamp ring 42.
There is a hole in the female clamp ring 42 that is the same size as, and concentric with, the body 43. This allows radiation from the flue pipe 4 to directly heat the bi-metal coil 60.
At the bottom of the inside of the thermometer body 43 a slot is cut to receive the tab from the bi-metal coil 60, and is clamped into position by set screw 63. Centered in the middle of the bi-metal coil 60 is bushing 61, the one end of the bi-metal coil 60 is bent over to meet the bushing 61 and spot welded in place. A needle shaft 64 is inserted in the bushing 61 and is locked in position with set screw 62. Needle 58 is attached to the end of the needle shaft 64. Scale plate 59 is positioned at the end of body 43 and behind needle 58. A glass lens covers the scale plate 59 and both are held in position by clamp ring 44.
As the flue pipe 4 temperature rises, radiation from the flue pipe 4 heats the bi-metal coil 60, causing it to rotate. This causes the bushing 61, needle shaft 64 and needle 58 to rotate. As the needle 58 rotates it indicates the temperature of the flue gases on a temperature scale printed on the face of the scale plate 59. The needle is prevented from passing the minimum and maximum of the desired temperature measurement range by two needle stops 57.

Claims

1. A variable combustion air control for wood stoves, comprising:
A wood stove flue pipe clamp to clamp to a wood stove flue pipe, A flue temperature sensing unit for detecting changes in the combustion temperature of said wood stove and for setting and maintaining a desired said combustion temperature;

A combustion air control unit for controlling the volume of combustion air to said wood stove using control information provided by said flue temperature sensing unit.

2. The variable combustion air control of claim 1, wherein said wood stove flue pipe clamp wherein one edge of said male clamp ring and one edge of said female clamp ring are joined together using a ball and hole means.

3. The variable combustion air control of claim 2, wherein said ball is attached to the said male clamp ring by a screw, a hole in said female clamp ring is larger than the diameter of said ball.

4. The variable combustion air control of claim 3, wherein said ball passes through said hole and said female clamp ring is held in position by said female clamp ring wedging between said ball and said male clamp ring.

5. The variable combustion air control of claim 1, wherein the opposite edge of said female clamp ring and the opposite edge of said male clamp ring are joined together by a male ball clamp, female ball clamp and bolt means.

6. The variable combustion air control of claim 5, wherein said female clamp ring overlaps and sits on top of the said male clamp ring and said male ball clamp is attached to said male clamp ring with a screw and said female ball clamp is attached to said female clamp ring with a screw.

7. The variable combustion air control of claim 6, wherein said bolt passes through a hole in said male ball clamp and is threaded into the female ball clamp.

8. The variable combustion air control of claim 1, wherein said flue temperature sensing unit means comprises a bi-metal coil.

9. The variable combustion air control of claim 8, wherein one end of said bi-metal coil is fixed to one end of a perforated metal tube, the other end is secured to a shaft.

10. The variable combustion air control of claim 9, wherein a bushing which has a tight fit in said perforated tube and is a loose fit on said shaft, said bushing guides said shaft where it exits said perforated tube.

11. The variable combustion air control of claim 9, wherein a lever is clamped to said shaft.

12. The variable combustion air control of claim 9, wherein the length of said perforated tube that is perforated matches the length of the bi-metal coil, the rest of said perforated tube is solid.

13. The variable combustion air control of claim 9, wherein said perforated tube is fixed to an inner race in such a way that they will rotate as one unit.

14. The variable combustion air control of claim 13, wherein said inner race is contained by an outer race and both are held in position in relation to each other by ball bearings that travel in grooves cut in both the said inner race and said outer race.

15. The variable combustion air control of claim 14, wherein said ball bearings are loaded into the grooves through a hole in said outer race, after which said hole is filled with a plug.

16. The variable combustion air control of claim 13, wherein indents are spaced evenly around a portion of the circumference of said inner race, and a hole in said outer race contains a ball bearing and a spring and is in alignment with said indents in said inner race.

17. The variable combustion air control of claim 13, wherein said inner race has a slot in a portion of the outside circumference, a threaded pin projects from the inner radius of said outer race in alignment with said slot.

18. The variable combustion air control of claim 1, wherein said male clamp ring is attached to the tube of said flue temperature sensing unit means, and the inside of said flue temperature sensing unit means has clear passage to the inside of said male clamp ring, allowing the inside of said flue temperature sensing unit means to receive direct radiation from said wood stove flue pipe.

19. The variable combustion air control of claim 1, wherein said combustion air control unit means comprises a lever.

20. The variable combustion air control of claim 19, wherein said lever is connected to a shaft, said shaft has a disk secured and that disk is contained in a control inner tube forming a butterfly valve means.

21. The variable combustion air control of claim 20, wherein said butterfly means is sized to match the combustion air requirements of said wood stove.

22. The variable combustion air control of claim 19, wherein the control outer tube is attached to a flange.

23. The variable combustion air control of claim 22, wherein said flange mounts to the said wood stove using screws.

24. The variable combustion air control of claim 22, wherein the control outer tube diameter is sized to match the flexible fresh air duct size, said flexible fresh air duct is typically clamped over said control outer tube using a stainless steel hose clamp.

25. The variable combustion air control of claim 1, wherein a light chain connects said lever of said flue temperature sensing unit means to said lever of said combustion air control unit means.

26. The variable combustion air control of claim 25, wherein both said levers have multiple attachment points for said light chain, for the purpose of matching the combustion air handling characteristics of said wood stove.

27. The variable combustion air control of claim 1, wherein said female clamp ring means comprises a bi-metal thermometer.

28. The variable combustion air control of claim 27, wherein the body is attached to said female clamp ring and the inside of said body has clear passage to the inside of said female clamp ring, allowing the inside of said body to receive direct radiation from said wood stove flue pipe.

29. The variable combustion air control of claim 28, wherein a bi-metal coil is supported by a groove and set screw in said body.

30. The variable combustion air control of claim 29, wherein a bushing is spot welded to a bi-metal tab at the center of the bi-metal coil.

31. The variable combustion air control of claim 30, wherein a needle is attached to a needle shaft and said needle shaft is clamped in said bushing with a set screw.

32. The variable combustion air control of claim 27, wherein a scale plate is located at one end of said body and behind said needle, a calibrated temperature scale is printed on the face of said scale plate.

33. The variable combustion air control of claim 27, wherein said scale plate and lens are retained on the end of said body by a clamp ring.