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Everything You Need to Know About C-Wire

If you’re upgrading to a new smart thermostat, a c-wire is a necessary addition, too. Short for “common wire,” the c-wire is needed to deliver continuous 24-volt electricity to the new thermostat. Unlike the older battery-powered thermostat it’s probably replacing, the new thermostat requires more power for new extras like Wi-Fi connectivity and the large touchscreen that makes access to smart functions so much easier.

Wired … Or Not?

In many recently-constructed homes, the HVAC c-wire is already installed. However, in homes that are only a few years old or older, the wire may need to be installed as part of the new smart thermostat installation. Here’s a simple process to find out in advance whether your house is already wired for the upgrade—or whether you’ll need that extra wire.

  • Remove the existing thermostat off the bracket that secures it to the wall. This is usually the same basic procedure you’ve probably done before to change the thermostat’s battery.
  • Once the existing unit’s removed, you will probably be able to see wires extending from inside the wall and connecting to terminals in the thermostat wall bracket. The wires will probably be various colors, however, color isn’t important at this point. What you need to do now is simply count the wires you can see.
  • If you count five wires (including any wire that might be loose or folded up) you probably already have a c-wire and the smart thermostat can be installed without any extra wiring required.
  • If you see only four wires, this means your house likely doesn’t include an HVAC c-wire and installation of the additional wire will be necessary.

Installing the required c-wire is a common procedure for any qualified HVAC service technician. Usually the new wire will connect to the control board in the furnace unit in order to complete the circuit that provides 24-volt electricity to your new smart thermostat.

For professional service to install a new smart thermostat and/or the required c-wire, contact Arpi’s Industries.

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