How to Install Thermostat Wires


Home heating systems use thermostats to maintain the correct temperature. Thermostats communicate with the furnace using low-voltage thermostat wires. Each thermostat function uses a different wire. Common home heating systems use four wires of red, white, yellow and green. The red wire is the power wire, the white wire controls the heating, the yellow wire controls the air conditioning, and the green wire controls the furnace blower. While it looks complicated, it is actually fairly easy to install thermostat wires and most home improvement enthusiasts should be able to tackle this project.

Things You'll Need

  • Tape measure
  • Drywall saw
  • Drywall anchors
  • Screws
  • Cordless drill
  • Level
  • 3/8-inch drill bit
  • Thermostat wire
  • Fish tape
  • Wire stripper
  • Screwdriver
  • Turn off the power to the furnace by turning off the correct breaker in the circuit breaker panel. Open the furnace access panel.

  • Locate on the wall where you want to mount your thermostat and cut out a hole in the drywall that is as large as possible but still can be covered by the thermostat wall plate.

  • Mount the thermostat wall plate on the wall using drywall anchors and screws. Check to see that it is level before proceeding.

  • Remove a section of drywall down by the floor. Drill a 3/8-inch hole through the floor inside the wall. This will be where the thermostat wire rises up from the basement to your thermostat.

  • Pull the thermostat wire from the furnace to the thermostat location using a fish tape. Pull the wire through the wall plate and leave about 4 inches of extra wire at the furnace control board and the thermostat location.

  • Strip the outer layer of insulation off the thermostat wire to expose the individual wires inside. You'll want about 2 inches of individual wires exposed on each end.

  • Strip 1/4 inch of insulation off each of the individual wires by the furnace and the thermostat.

  • Connect the red wire to the "R" terminal on the furnace. Connect the white wire to the "W" terminal on the furnace. Connect the green wire to the "G" terminal on the furnace and connect the yellow wire to the "Y" terminal on the furnace. These terminals should be located on the control board inside the furnace. Put the furnace access panel back on to the furnace.

  • Connect the wires up to the thermostat to the same lettered terminals as you did in the furnace. Push the thermostat onto the wall plate until it snaps into place.

  • Patch the drywall where you cut the access hole by the floor.

  • Turn the power back on to the furnace and turn the thermostat to your desired setting. It should now properly condition your house per your settings.

Tips & Warnings

  • The power to the furnace must be off when installing the thermostat wires. Not only can live power fry the control board, you could suffer an electrical shock from internal components of the furnace.

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  • Photo Credit Ryan McVay/Photodisc/Getty Images
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