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Hello, is my Nest Thermostat E compatible with my existing wiring?

Community Specialist
Community Specialist

Disclaimer: This thread was migrated from our previous version of the Google Nest Community. You can continue to receive updates on your thread issue here or simply ask, browse or more in the new Google Nest Community.

Original Poster: Dpj 

Determine compatibility, and how to wire


Community Specialist
Community Specialist
Hi Dpj, 
Thanks for reaching out to us and welcome to our community! I'd be happy to decode your wiring setup. 
Just for clarification, here's what your photo shows: 
  • O: This is usually an auxillary heating wire, or a changeover valve that switches between hot and cool. 
  • R: The R wire is the power wire for your heating and cooling system. If you only have one R wire (no Rh or Rc), you can connect your R wire to either Rc or Rh on the Nest thermostat.
  • B: Sometimes this is paired with the O wire, but it can also be a common wire (c-wire), which helps your Nest Thermostat charge. I would consult with a Nest Pro to ensure which wire it is. 
  • X2/W: This looks like your heating wire, but to the best of my knowledge, the X2 port is uncommon in use with the thermostats. 
  • Y: This controls your cooling system. 
  • G: This controls your fan. 
It looks like it would support a Nest Thermostat, but needs a professional lookover to make sure its installation doesn't damage your HVAC system. 
Hope this helps! Let me know if you have any further questions for us. 
-From Ai, Community Specialist.