Wiring a second thermostat

Tcatrider99 Posted By Tcatrider99, Nov 8, 2018 at 8:59 PM

  1. Tcatrider99

    Tcatrider99
    New Member 2.
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    Nov 8, 2018
    2
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    Loc:
    Newport NY
    Year's ago I had an outdoor boiler and am currently hooking one up again. I have everything hooked up but I'm stuck on how to wire in my second thermostat. What I have is a thermopride oil fired furnace with a heat exchanger in the plenum to transfer heat from the OWB. I want to retain use of the oil furnace (set at a lower temp) in case the OWB goes out. I want the second thermostat (set at a higher temp) to run the furnace fan to blow through the exchanger in the plenum. I had this set up on my last system but cat remember how to wire it. The second thermostat I'm using is a white Rogers 110v. Any help would be extremely appreciated.
     
  2. E Yoder

    E Yoder
    Member 2.
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    Jan 27, 2017
    192
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    Loc:
    Floyd, VA
    If you don't have AC and 24v.terminals you might have to relay the actual 110v. fan wire.
    What I'm describing below is just a guess not having seen the wiring.
    I'd use a second transformer to run the second t-stat, and a 90-370 relay (spdt) to start the fan.
    W on the new thermostat would power the 24v
    coil on the relay, and the NO would have constant 110 v. power to it, NC would be fed by the original fan power, the terminal common to both NO & NC would go on to the fan.
    Basically fan power just runs straight through the relay as it did originally unless the new stat calls for heat. Then it breaks from original source and sends 110v. power also but it can't backfeed.
    Clear as mud I'm sure. I don't have the relay numbers in my head, I think the coil is 1 & 3.
     
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  3. Tcatrider99

    Tcatrider99
    New Member 2.
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    Nov 8, 2018
    2
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    Loc:
    Newport NY
    The second tstat (that is the one that was used when we had this set up before) only has the power, neutral, and ground wires coming out of it and running to the furnace (but not hooked anywhere currently). I don't remember ever having a second relay. This pic is of the wires in my oil furnace. Not sure if that helps..., 1108182003.jpg
     
  4. E Yoder

    E Yoder
    Member 2.
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    Jan 27, 2017
    192
    26
    Loc:
    Floyd, VA
    Yes, that's a relay and transformer hanging down. Called a fan center, does the same thing.
     
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