[Foureagles]

My old house relies mainly on a wood stove for heat, but also has a propane forced-air furnace located upstairs – no A/C. The return-air opening is directly above the wood stove. Originally, it used a manual-switchover heat/cool thermostat with 3-wire hookup to the heat side only. This was located downstairs, near the wood stove.

I installed a programmable thermostat upstairs, & disconnected the original one at the furnace. I’d like to still be able to control the furnace blower from the downstairs thermostat, preferably automatically by using the “cooling” side, so that the blower will come on & distribute heat from the wood stove, then shut off & revert to the upstairs program when the fire dies at night.

Is this feasible and, if so, how would I wire it? Thanks.

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[labman]

I don't think the A/C contact would work, because you must switch the thermostat from heating to cooling manually. You would also have to add a relay to ''not'' the A/C signal. If your furnace has a G or Y terminal, you could connect the W from the old thermostat to it, which would start the blower, likely on a higher speed than the furnace heat cycle. If that is a problem, get back with me. If you are going to use the old thermostat to activate different coils in the furnace, it should be simpler to power both thermostats from the same transformers. If you use 2 transformers, you must have them in phase.

Does your thermostat have multiple firing rates, W1 and W2 or other labels? If so, you could leave W1 connected to the blower, and connect W2 to the gas valve. Thus when the thermostat calls for heat, it would activate W1 only starting the blower. If that didn't heat the house up very quickly, the thermostat would then activate W2 firing up the propane. Check the directions for your thermostat and see if says anything about high and low firing rates. Your 3 wire cable would work unless you need a wire for the common. Red from the transformer, and white for W1, and the other color for W2.

Dual rate furnaces are common. Mine is, but I have a simple thermostat and let the board in the furnace determine the firing rate.