While we find that in 99% of homes Nest can charge its built in battery using regular heating and cooling wires, for a few installations Nest does require a common wire to bring power to the thermostat.

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Here are some installations that may require a common wire to work with Nest:

• Many zone relay panels or control panels. 
  Nest requires a common wire to be compatible with many zone relay panels. Some systems have control panels or equipment interface modules that require a common wire to be compatible with Nest. Here’s a list of known panels that require a common wire:
  • Honeywell AQ25110B
  • Honeywell EMM-3
  • Honeywell TZ-4
  • Honeywell HZ311
  • Bryant 548F036
  • White-Rogers 36C03-300
  • Carrier HK42FZ011
  • Nordyne 624631-A
  • Nordyne 903915A

• Some gas valves. 
  Some gas valves on systems vibrate or buzz when Nest is installed. This can usually be fixed with a common wire. 

• Some micro-controller based systems. 
  Systems that use micro-controllers instead of relays are sometimes more sensitive to power-sharing. If so, Nest will need a common wire to be compatible with these systems.

If you have questions about your installation and whether your home will need a common wire, please contact support using the information at the top of the page. We're here to help.