How to Wire a 24-Volt Thermostat

Thermostats control the furnace and tell it when to turn on or off based on the temperature setting. Thermostats typically have 24 volts of power that are extended to them from a furnace's circuit board. When the temperature forces the thermostat to turn on, the circuit is closed. This powers up the furnace. Once the desired temperature is reached, the circuit opens and the furnace stops. The wiring must be connected to the correct terminals on a 24-volt thermostat for proper operation.

• 1

  Turn off the power to the furnace. Lift off the front access door.

• 2

  Find where the thermostat's wiring connects to the circuit board. Mark each colored wire and the corresponding terminal to where it connects. Replace the access door.

• 3

  Go to your thermostat. Strip the end of each thermostat wire back a half inch to expose the copper.

• 4

  Connect each wire to the correct terminal indicated by your notes. Each colored wire must connect to the corresponding lettered terminal on both the thermostat and the furnace.

• 5

  Push the thermostat back on to its mounting plate and restore power to the furnace.

• 6

  Test the thermostat to verify that it turns the furnace on and off.