I've been wanting to upgrade my thermostat to a smart one -- I only have an in-floor furnace, so the utility isn't super necessary, but I'd like to have a smart thermostat anyway (so I can turn my heat on as I'm making my way home).

I believe I have a millivolt system -- as I have a Honeywell TS812A1007, which is a millivolt controller. I've read online that it is possible to uprade to a smart thermostat, but that I'll need something like a 24VAC Transformer

Below is the back of my thermostat:

Back of Thermostat

My questions is: is this 24VAC Transformer something I can just add on to where the thermostat lives (i.e., is it just a need for power to the thermostat) -- or do all of my options involve adding a new wire from my furnace? I've got a hunch that snaking a new wire up to the thermostat from the furnace will be the most difficult/expensive part, so if I can just run a plug to the new thermostat and have it use that + the 2 existing wires, then this won't be too difficult.

I've been trying to make sense of the thermostat schematics people have posted, but I am very novice at electricity/wiring (and by novice, I mean I got a C in high school physics and that's the extent of my expertise).

  • 1
    Do you know where those wires depart? There is a very high chance arrangement is a live coming in and a switched live going out to the circulation pump. – ratchet freak Nov 22 '16 at 9:19

The Honeywell TS812A-1007 is a heating only, 24 volt thermostat, not a millivolt thermostat. The millivolt one is a different part number. If you have a volt meter, turn the thermostat all the way down and check the voltage across the 2 wire connections; you should get 24 volts. If you don't have a volt meter, look at the gas valve on the furnace. It should tell you the voltage required for that valve. If you need to change the wires to upgrade the thermostat it is not that hard, but you may be better off getting an HVAC guy in since they snake wires all the time.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.