Nest thermostat compatibility

[Evanmichael556]

Can someone help me find out if my system is compatible with the Nest thermostat? I've tried the compatibility checker, but it asked me to consult someone after I confirm I do not see a "C" wire.

[laurentbourg]

Having a C wire is definitely preferred, but a lot of the time it works without one. It is hard to predict for sure because there are various variables that come in consideration (type of furnace, custom setups etc)

[Evanmichael556]

What exactly does the C wire do?  Will I be losing out on functionality if I buy a nest and I don't have the C wire? 

[laurentbourg]

The C wire provides power to your thermostat. It is normally able to take power from the R wires when not available, but that process is not always compatible. You would not lose any functionality if it works without it, otherwise you will need an HVAC technician to install one for you. There is also C wire adapter/transformer you can install yourself that plugs into a wall socket, but you will see a wire on your wall going from the outlet to the thermostat, which is not always esthetically pleasing.

[Evanmichael556]

Thank you, this is very helpful. Is there any way to know for sure if the R wires will work as a substitute for the C wire in my specific case?  Definitely not interested in having an outlet by the thermostat.  I also don't want to buy a Nest only to find out it doesn't work after all.

[laurentbourg]

Unfortunately there is no guaranteed way and anybody that will tell you otherwise is not fully knowledgeable. Buying a Nest at a retailer where returns are an easy process might not be too much of a hassle, moreover if you really wanted to keep it, your setup is for sure compatible, you would just need a professional to wire the C.

[sporfrog]

Just out of curiosity is there a "C" under that blue wire?  That thermostat looks like maybe it has 2 rows of labels depending on the type of heating.  The upper row for traditional, and the lower row for heat pump.  Do you know which applies to you?

[laurentbourg]

The partially hidden letter on the top row behind the blue wire should be a "B", not a C.

[laurentbourg]

Evenmichael556, your system is compatible, it’s a heat pump for cooling and heating with an electric auxiliary heater. Please connect as follows on the Nest learning thermostat:

- brown to W2 Aux
- white to OB
- blue to C
- yellow to Y1
- red to Rc