Tying in LP furnace fan with Wood furnace fan

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weloveburning

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Did a search and could not find the answer to this question on here. Have any of you that have a thermostat on your wood furnace been able to tie that into your LP furnace fan for more push when the Wood Furnace fan kicks in?

Wondering weather we would go directly to the furnace with a wire from the Wood burner thermostat, or go to the LP thermostat?

I hope that I'm making sense here. Basically we want the LP furnace fan to kick on and off at the same time that the fan on the Wood furnace kicks in, thus pushing more of the hot air supplied to the LP furnace by the wood furnace fan.

Any suggestions???
 
is your wood burner not pushing hard enough ? im no expert but i know you can get a inline duct fan to increase flow they are on ebay pretty cheap i was going to use one if needed there 110 volt you could tie that in with wood burner fan come on same time like i say im no expert but where thers a will theres a way.
 
I hear you. Actually the Wood furnace has a beefy 850 fan on it, but it just doesn't quite get the heat to the back bedrooms. I can manually turn on the house furnace fan, and get the heat there without issue, so if I can tie the thermostat to the house furnace fan so that it kicks on at the same time, I'm good to go. I know it can be done, just not sure to wire to the house thermostat or direct to the fan on the furnace, from the thermostat on the Wood Furnace. :confused:
 
There's a schematic on the inside panel of your furnace, look for a terminal board that shows fan control wiring from your house thermostat. Follow the wiring diagram and you should be able to do it. Turn the breaker off first though, no need to be poking around in there with the power on.

For mine, I put in a seperate temperature probe in the plenum, wired that into the main furnace fan, so when the duct has the hottest air the larger fan runs for a few minutes, then shuts off. The wood furnace fan runs constantly, and having the larger fan also running that much would lower the mean temperature too much.
 
furnace fan tie in

Best way is with a relay with 120 volt coil. Connect the relay coil to wood stove fan and use relay contacts to imitate the fan switch on LP furnace thermostat. This avoids the danger of burning up LP fan, easy to do if it is a multi speed motor and you power more than one speed at a time. When wood fan comes on, relay pulls in, relay tell LP fan that it should run, then relay in LP furnace switches LP fan on just like you switched the fan switch on LP thermostat. You may have to turn breaker for AC unit off to keep the AC unit from running as the fan switch on LP thermostat connects the green fan relay wire to the yellow AC unit wire when the fan switch is in the off position. This enables the thermostat to cycle the fan with the AC unit when fan switch is off.
 
Best way is with a relay with 120 volt coil. Connect the relay coil to wood stove fan and use relay contacts to imitate the fan switch on LP furnace thermostat. This avoids the danger of burning up LP fan, easy to do if it is a multi speed motor and you power more than one speed at a time. When wood fan comes on, relay pulls in, relay tell LP fan that it should run, then relay in LP furnace switches LP fan on just like you switched the fan switch on LP thermostat. You may have to turn breaker for AC unit off to keep the AC unit from running as the fan switch on LP thermostat connects the green fan relay wire to the yellow AC unit wire when the fan switch is in the off position. This enables the thermostat to cycle the fan with the AC unit when fan switch is off.

+1
 
Its the easy way out but I leave my furnace fan run all the time. HVAC man said furnace was designed to run like that.At night I shut the fan off and let furnace run on cycle. :)
 
done it .have not tried it this way . about told the way I did it afraid if you did this way an you burn gas to it would fry blower motor . use a solenoid or relay. should able to get one at granger or electric supply this going to be really hard for me to explain. your going to have jump the 2 wires off your wood furnace to the hot side of the solenoid . now the gas furnace need one hot wire run to the contunity side of the solenoid an the fan motor to the other side . if anyone can get the just of this an can put pics on here . would be a big help .
 
done it .have not tried it this way . about told the way I did it afraid if you did this way an you burn gas to it would fry blower motor . use a solenoid or relay. should able to get one at granger or electric supply this going to be really hard for me to explain. your going to have jump the 2 wires off your wood furnace to the hot side of the solenoid . now the gas furnace need one hot wire run to the contunity side of the solenoid an the fan motor to the other side . if anyone can get the just of this an can put pics on here . would be a big help .

You are correct, as we went to a local shop for the relay and the wire, and he drew us up a diagram on how to accomplish this. I'm going to post it here for others, in case they need it. The relay is the heavier one with a 120V coil.

furnace-wiring-diagram.gif
 
This is a lot easier to do with older furnaces that did not have an integrated furnace control and instead had a mechanical fan switch that responded to plenum temp, just like a wood furnace would have. In this system you would run a hot wire from the fan switch on the wood furnace in parallel with the fan switch in the furnace, so when the fan switch in the wood furnace kicks on, both fans will run as long as the plenum temp of the wood furnace is warm enough. On a newer furnace with an IFC you would have wire the control board to kick the FAN mode on, just like for cooling. Here is where the danger of energizing the fan on two speeds comes in, if there is a normal call for heat from the gas furnace when the fan is on it may cause it to start on the heating speed. Some kind of isolation relay is needed in this case to keep the fan motor from burning out.
 

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