CLEANING UP WOOD HEAT FOR 1982-83

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[15] Crimp 1/2" of each end of the tube — either by using a vise or by hammering — then drill a 1/8" hole in the side of the 1/2" pipe, insert the end of a 1/8" X 11 " (or long enough to reach a point where the temperature will never be higher than 250°F) copper tube, and silver-solder the crimps and the tube junction. These joints will be outside the stovepipe during operation to prevent any possibility of deterioration.

[16] Cut a 1"-high, 5"-wide slot in your stovepipe at a point 12" above the location at which you've been checking stack temperatures. (If you're working by guess, try cutting the slot 4 feet up . . . but be prepared to try again if you don't get enough adjustment range.)

[17] Plumb the sensor tube to an appropriate length of 1/8" nylon tubing, using 1/8" windshield-washer hose. You can also prepare the connector hose for the diaphragm end, but don't attach it just yet.

[18] Turn the adjustment knob clockwise until the chamber is set at maximum volume.

[19] Light a fire in the stove and leave the door(s) cracked until you see a stack temperature, of about 400 °F on the internal probe thermometer (or about 300°F on a surface temperature thermometer . .. or what seems like a pretty hot fire if you're guessing). At that point, connect the last tubing junction and close the doors.

[20] Turn the adjustment knob to achieve the desired heat output.

HOW WARM FOR HOW LONG

We've recorded the heat being given off by our thermostat-equipped stove in an insulated room, and have found that stable stack temperature correlates closely (but not exactly) with steady heat production. By watching door temperature, we've noted that the stove reaches a slightly higher surface temperature about two-thirds of the way through a burn. A thermostat controlled by door temperature wouldn't allow this to happen, but we doubt that most folks will even be able to detect the small change in heat output involved.

Though we've run our stove at burn rates of as low as 1-1/4 pounds of wood per hour, it's unlikely that many people will be interested in outputs that low. Of course, a load of wood lasts for a very long time at such a rate (we've run 16 hours on one fuel charge and don't doubt that we could go longer), but the heat given off by the stove is minimal . . . while creosote accumulation is dramatic!

Judging from our own experience and from published information, most home woodstoves are run at burn rates of between 2 and 4 pounds per hour, which is the range at which our thermostat does its job best. If however, your heater is substantially different in volume and/or design from the one we've worked with, you may find that the size of the valve, the location of the sensor, and/or the range of the adjustment chamber will have to be changed. We've tried to build a thermostat that suits an average space heater, but we do believe that — with the modifications mentioned above — it could be made useful for almost any wood-combustion appliance.

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