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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am replacing and old mercury honeywell thermostat with a

Customer Question

I am replacing and old mercury honeywell thermostat with a programmable one. The old thermo had a black and a white wire. 14 gauge. On the new Honeywell rth6400 can I just put the black on the R terminal and the white on the W? They are 120v
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: I am replacing it for aesthetics. It's a simple tstat question... I hope lol
JA: Do you plan on doing the work yourself?
Customer: Yes
JA: Anything else we should know to help you best?
Customer: No
Submitted: 8 months ago.
Category: HVAC
Expert:  Rick replied 8 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can

continue our conversation.

The rth6400 is a 24 volt thermostat. You can't use it on a 120 volt circuit.