I'd like to replace my Honeywell CT87A thermostat with a Nest thermostat. I see that Nest has a page to check system compatibility. Is it possible to identify if my system is compatible without taking it off of the wall, perhaps by the fact that I have a CT87A? It's bitter cold out and I don't want to turn off the fuse for the furnace.


According to the installation instructions in your link, the Honeywell CT87A requires only two or three wires (R,W,[Y]) to operate. The Nest compatibility checker shows that a system using those wires is compatible. You should be good to go.

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