DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > One thermostat, two heat sources

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Old 02-15-2008, 12:12 PM  
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Default One thermostat, two heat sources

I have a gas fireplace and an oil furnace that I would like the ability to switch on or off as my heat source. I would like to use one thermostat and have a switch that would either point to fireplace or furnace as the source.

Can I just run the current wires from the thermostat into a switch, and have the switch close the appropriate circuit, or is there another way?

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Old 02-15-2008, 04:57 PM  
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the purpose of the tstat is to power certain circuits inside the heat unit.
how would you manage to send power to the appropriate unit & circuit? You'd have to switch over all wires in the tstat.

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Old 02-17-2008, 06:04 PM  
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i would suggest you use a double pole double throw switch connect the thermostat in the middle and the units on each side hope this helps if you need a sketch let me know good luck
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Old 02-17-2008, 10:32 PM  
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Default what????

I think what your wanting to do has never before been attempted. Given that, I feel the price of two switches, cutting them in wall, possible drywall repair, wire, and not to mention the fire place uses mili amps for ignition circuit, and furnace uses 24volt a.c. Your far better off getting a separate t-stat for fire place. Check with your local f.p. dealer for correct type, then go to the cheap place and get one. Remember this is just one man's opinion, good luck....
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Last edited by triple D; 02-18-2008 at 05:49 PM.
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Old 02-25-2008, 07:58 AM  
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hey folks,

thanks for the replies.

I had the intention of using a switch with 4 contacts, so I would be switching all wires in the circuit. When one circuit is in use (i.e., in the 'on' position) the other circuit would just be open, as if no thermostat was installed. My furnace is 24volts, but not from the thermostat, and the fireplace is just looking for a closed circuit (2 wires are provided for this purpose).

I want both systems to be controlled by one thermostat so only one system is on at any giving time. I cringed when I see the fireplace on, and the furnace going.

I don't think I'm doing anything unusual, but perhaps I am.....
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Old 02-25-2008, 08:30 PM  
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Default Naaa

Sounds like you have something to invent....better get a patent.
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Old 06-19-2008, 08:56 AM  
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Default the right t-stat

listen and please forgive the spelling you need a honeywell pro6000 with a 2 heat option pick your primary heat source and wire that to w and secondary to aux or l . you can not mix the input signal so use the 24 volt from the furnace and your output 24v signal to the fireplace and wire this to a rib relay useing the out put signal and common to make the switch and wire the fireplace wire to the closed contact side . this will allow your primary heat to run unless there is more then a 4 degree temp diff between set point and room in which case the both would run or if you where to select emergency heat on the t-stat then only the secondary heat would run . I have retrofit systems like this before and it works well but the thermostat location is criticle if you use your fireplace as first stage. there are other duel feul controls not nessaserily designed for this but might work and are going to cost more.
ps make sure to program the t-stat for a 2 heat 1 cool heat pump
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Old 06-19-2008, 05:42 PM  
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Never run across a situation like that before, so I'd be especially interested to hear if you can pull it off. I tried to do the research on the Honeywell model mentioned above but couldn't find much about wiring it.

Here's the link for the thermostat he's talking about:

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