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Combining Thermostats

Yorkie
Yorkie Member Posts: 1
in Thermostats and Controls

just moved into a new home and we have two thermostats. One is for the AC which is a new unit with a relatively new none smart thermostat. This has green, yellow and red wires and a jumper. The other is for our fuel oil water boiler that has a very old thermostat with only a red and white wires.

I would like to replace both thermostats with a single smart thermostat. Will this work? Any tips on how to do it successfully?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,696

    Well… yes, it can be done. There are a number of thermostats available, from several different brands, with varying degrees of "smart". Most of them can be programmed — with varying degrees of ease and rather widely varying degrees of functionality — to handle systems with both AC and fuel fired equipment.

    Unfortunately, each application is somewhat different, so the only "tips" I can think of, without having the specific application to hand, is to carefully read the installation and programming instructions, on the one hand, and to really spend some time thinking about what you presently have in the way of wiring and power sources for the thermostat.

    I will admit that my personal preference is to keep the "very old" thermostat for the heat. The chances are that it works at least as well, and more reliably, than any newer digital or smart thermostat would — but I grant that it isn't "smart".

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jtaylor
    Jtaylor Member Posts: 1

    I'm just a hack so take this for what it's worth. I did this, but both my AC and Boiler are relatively modern. My current thermostat is battery operated, so I just wired both systems as if I was wiring them independently.

    If I change to a Nest or something, My AC air handler would power the smart thermostat because the thermostat wire going to the boiler is only two wire, like yours.

    My AC has a breaker for the air handler and another for the compressor. As part of my winter prep, I turn off both breakers to the AC unit. Therefore, I would have to keep the air handler powered.

    Thermostats are a switch, and complete the circuit when they call for heat. However, you should determine if both systems are the same voltage. Mine are both 24 volt. I have no clue what would happen if one system was 12 volt and the other 24 volt. Also, some boilers use(d) line voltage (120 volt AC) for thermostats. It sounds like yours is likely 24 volt simply based on the color of the wires you described, but you need to be cautious.

    The way I have mine configured has been working great.

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