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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am trying to replace an old two wire thermostat with a

Customer Question

i am trying to replace an old two wire thermostat with a progammable one. the old thermostat only has two black wires so not sure which wire to put where on the new one
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: thermostat
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: no
Submitted: 12 days ago.
Category: HVAC
Expert:  Rick replied 12 days 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 wires would go on the R & W terminals. It doesn't matter which leads you connect to R or W. I suspect you have a millivolt system so your new thermostat would have to be battery powered and millivolt compatible.