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Thread: two heating systems off of 1 thermostat?

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  1. #1

    Default two heating systems off of 1 thermostat?

    I have a geothermal system run off of a thermostat. Also I have a Alaska coal furnace run off of a thermostat. The two heating systems are fighting. Iím told that I can put a relay on the Y1 wire and turn on the coal furnace when the geothermal thermostat calls for heat. Can someone tell me about this relay?


  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    A thermostat is basically a temperature controlled switch. To turn on a heating device, all you need is to connect the two thermostat wires together. A simple single-pole 24vac relay will be fine. Basically, connect the relay with the two leads of the thermostat from one heating system you want to control on the common and normally open sides fo the relay, and the coil wires connected to the common and output of the thermostat from the other. Then, when one system's thermostat turns on, it will energize the relay, emulating the thermostat of the other furnace.

    If you search on isolation relay, you should get some examples.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3


    Thanks Jim,

    >> ... search on isolation relay ...

    Now I see. I do electronics for a living instead of electricity or heating/cooling. The terminology was the source of my confusion.



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