I finally filled my system yesterday and I am now ready to start with the control side. As always I need help from you guys. I purchased a 2 stage heat thermostat that I would like to control my propane furnace and secondary circulator pump/furnace fan. I have an adjustable thermostatic switch screwed into the top of my storage tank and a 24volt / 120 volt relay. My furnace has a 24volt transformer inside and I just ran new thermostat wire with 8 circuits inside. I was planning on putting the thermoswitch and relay in series with the first stage heat(W1) so I could control that circuit based on storage temperature. I was going to wire W1 to the Fan on circuit on the furnace control board so W1 would turn on the fan only but it looks like it would back feed the green wire (G) circuit. When I ordered the relay and thermoswitch I didn't completely understand how a thermostat worked. I didn't realize that the thermostat closed the fan contact (G) and the heat(w) contact at the same time for heat the the same for cooling, (G) and (Y). I thought it only closed (W) or (Y) and the furnace controlled the fan on its own. Since this is not the case I have the issue with backfeeding on the (G) fan wire. Hope I didn't confuse everyone.
Wiring two stage thermostate to new boiler install
- Thread starter hartkem
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I think I misunderstood how the heat mode works. I assumed the thermostat turned on the heat (w) and fan (G) but since this is a propane and not electric I believe only heat (W) turns on. The furnace then turns on the fan on its own when the temp is high enough. I simplified the circuit a bunch but still concerned about the Furnace circuit board handling the draw of the primary relay coil.
heaterman
Minister of Fire
What make and model furnace do you have?
Most newer gas furnaces energize from r-w on a call for heat and r-y&g for cooling. In heating mode the furnace board will energize the burner circuit and the blower on is controlled by a fan timer built into the board.
We usually install a separate thermostat for heating in "wood mode" and energize the G terminal only by using an isolation relay to take Y out of the system. Been a while since I have done one but it seems like I have installed a DPDT switch to go from summer (cooling mode) to winter (wood heating mode) .
I don't think a normal two stage stat is going to accomplish what you want to do. You'll wind up with both heating modes running at the same time.
Most newer gas furnaces energize from r-w on a call for heat and r-y&g for cooling. In heating mode the furnace board will energize the burner circuit and the blower on is controlled by a fan timer built into the board.
We usually install a separate thermostat for heating in "wood mode" and energize the G terminal only by using an isolation relay to take Y out of the system. Been a while since I have done one but it seems like I have installed a DPDT switch to go from summer (cooling mode) to winter (wood heating mode) .
I don't think a normal two stage stat is going to accomplish what you want to do. You'll wind up with both heating modes running at the same time.
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