Wood furnaces

I have a fan/limit switch with a probe that goes into the plenum on my wood burning furnace .....What happens is that I start a fire in my wood burning furnace where the ductwork is tied into my oil fired furnace .....When the temps get up to where I have them set on my fan limit switch, it's wired to the fan on my oil furnace, and the fan kicks on .....The air is pulled from the plenum of the wood furnace , and it cools down and the fan shuts off ....It cycles like this about 3 times while the fire is building , and then the fan stays on and blows warm air thru all the duct work ....I also have a hand regulated duct in the basement that I can open or close ...I leave it cracked open so that the basement get's warmed while the upstairs also get's warmed ....There is an thermostat for the oil furnace , and also a thermostat for the wood furnace ...I turn the oil thermostat all the way down , and the wood thermostat up to the temp I want ...Its not very accurate , but it sure gets nice and warm in the cabin ...If I let the wood die down , the air in the plenum gets cold, and shuts the fan off ....I have my oil thermostat set to 60 degrees so that if fire goes out in the wood furnace, and shuts down , and the room cools all the way down to 60 degrees , the oil furnace will fire .... This never happens as I feed the wood furnace till the house gets up to 75-80 degrees and it takes a while for it to drop down to anything under 65 ..... I put enough wood in it that it will run until about 12 midnight , and then let it slowly drop from there ...If it's 25-30 degrees outside , by the time it's 6-7am the house is still at about 65 degrees or so ...When it gets colder out, I can add more wood for the fire to continue longer .....Jim

Not quite what I was talking about - I hope...

There are two air supplies that one needs to worry about w/ forced air heating. One is the air that gets circulated around the house after being heated. I think this is the air supply you are thinking of John. It can come from the general basement, but then one needs to make sure there is adequate air return from the rest of the house to the basement, and possibly about any excess radon in the basement.

The second supply is the air that feeds the fire, and which should be getting sent out the chimney along with all the noxious smoke. In many setups this is just air coming from the general basement area, which isn't a problem in and of itself, but which CAN be an issue if there are not enough sources of "makeup air" to replace what the fire consumes. This is especially the case if there are two or more air consuming appliances in the same area, as if the makeup air supply is not adequate, one appliance can reverse the flue of another in an effort to pull it's makeup air in through the chimney - this sort of works, but also can introduce carbon monoxide and other fumes into the house.

Solution is to supply outside air to one or more of the appliances so that you reduce the demand for makeup air.

Gooserider

we use a temp. controlled relay switch in the cold air return of our HVAC. when temp get high enough in the cold air return, the squirrel cage kicks on. no blower on the furnace itself...gravity induction to CAR. besides that, your funace fan shouldn't be drawing much amperage, and you can never have enough circulation IMO.