Agreed! I looked up the manual online, and found this which is why I mentioned 24vAC:
https://www.manualslib.com/manual/194531/White-Rodgers-1e30-W.html#manual
ELECTRICAL DATA
Switch Rating: 24vAC (30vAC max.)
Adjustable Heat Anticipator - 0.15 to 1.2 Amps
Switch Action: SPST - Sealed mercury switch
THERMAL DATA
Temperature Range:
Standard = 10 to 32 C (50 to 90 F)
Low Range = 4 to 24 C (40 to 75 F)
Differential: 1/2 C (1 F)
There's a chance that this is a different sub-model from what I have. My recollection is that it would have been installed in the 1990s along with the fireplace.
I suspect it just opens/closes a contact when the temperature transitions across the set point. There's a 2 wire cable coming out of it over to the fireplace. Looks a lot like lampcord.
I have an ecobee 3 lite used for our furnace. Looking for something similar for the fireplace. I assume that it will need to be battery powered, given that I don't think the 2 wire connections are useful for power.
