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I don’t have a common or “c-wire" and need one. What are my options?

Sensi thermostats work with most heating and cooling systems, however, the need for a common wire or “c-wire” is different based on the Sensi thermostat model. Unsure if your thermostat needs a c-wire? Reference the master compatibility chart in this article.

If you need a c-wire, there are a few main options:

  • Using an extra, unused wire as a c-wire
  • Using your thermostat’s g-wire (fan wire) as a c-wire
  • Installing an Emerson Thermostat Common Wire Kit

If you would like to understand what a c-wire is and learn more about these three options, watch our helpful videos on our c-wire page.

One of these three options work on most HVAC systems, however, if you have a 2-wire, heat-only system, you will need to run a new wire from your furnace to your thermostat or install a 24VAC power transformer to supply constant power to your Sensi thermostat.

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