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WeaknessNegative392 OP t1_ix8i0t6 wrote

Reply to comment by lefos123 in Replacing 120v thermostat by WeaknessNegative392

Sorry maybe should’ve added a bit more detail for context but this isn’t a new install. The entire heating setup is from the late 80s. I just bought the house and wanted to update the thermostat to a programmable one in hopes to cut down on unnecessary heating when no one’s home. But 90% of the stats out there now are 24v. I did find one 120v stat but it said right on it not for hot water baseboard. But I will definitely look into the transformer/converter, thanks for your help!

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lefos123 t1_ix8icjr wrote

I wish you luck on this one. Not sure what is up though. Our house is New England 1975. Same heating setup. And it’s 24v. We do have a 120v thermostat but that’s for electric baseboard heat in a bonus room.

So when whoever installed this originally. I’m surprised they went 120v

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assholetoall t1_ix8p020 wrote

Confirming the New England houses I've lived in from the 40s, 80s and 90s all used forced hot water from a boiler with a 24v AC control system which includes the thermostat.

Two did also have electric baseboard that ran on 240v, but it was very separate from the 24v system.

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Way2Saucy4U t1_ixbzjx8 wrote

Unless I’m misunderstanding, I don’t think this idea will work.

In most programmable thermostats, the “R” terminal on the thermostat is both the source voltage to power the thermostat and is also the same power to each energized output.

Think of the thermostat as a switch to each output. The thermostat makes decisions about when to switch ON the signal voltage from the furnace power source back to the furnace devices/controls which operate the heating functions (ex. relay, contactor, etc…)

You definitely can use a transformer to step down the 120V power but the 24V thermostat outputs will also be 24V back to the furnace. In order to make this idea work, each thermostat output would individually then need to be transformed back to 120V since the current controls internal to the furnace or controls associated with your heating setup are looking for a 120V signal.

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