Replacing old thermostat with a Sensi Smart therm.

[Hawksnest101]

Heat only system/ thermostat. Sensi needs a common wire to power same which I have and traced it to the hot water furnace. Can I connect the C (common wire) to the transformer located on the furnace to get the required 24 volts? If so to the terminal that has a red wire connected to it? Thank you

 

[Fitter30]

Take a pic of the wiring diagram on furnace. Back of blower door.

 

[Sponsor]

 

[WorthFlorida]

Yes you can and must use the same transformer from your heating plant (furnace, boiler, etc) that the thermostat is connected to.

Depending on the age of the thermostat wiring, any spare wire in the thermostat bundle can be used to connect to the transformer and C terminal at the thermostat. Usually a black wire is used. The Smart Thermostat gets its power from the RH or RC terminal.