- Identify the wires: You need to connect the correct wires to the corresponding terminals on the back of your new thermostat. The standard color code for thermostat wires used in most systems is:
W - White wire connected to the heating system Y - Yellow wire connected to the air conditioning compressor G - Green wire connected to the fan Rc and Rh - Red wires that are the power source for your thermostat. If your thermostat is dedicated to air conditioning only, it will have a red Rc wire. For heating and cooling systems, it will have a red Rc and a red Rh wire. C - Common wire that provides smart thermostats with continual power. It's usually blue, but it may also be black, brown, or purple. O - Orange wire that connects to your heat pump (if applicable).
Turn off the power: Turn off your existing thermostat and the power to your HVAC system at the main breaker box.
Find the common wire: Look for a wire connected to a terminal labeled with a "C" on the thermostat. If you have one, that’s your c-wire, and you’re ready for general installation.
Label and disconnect the wires: Identify and label the wiring in your existing thermostat before you disconnect the wires. Take a picture of your current wiring scheme and disconnect the wires and the corresponding mounting screws. The backplate from your thermostat should come free. Tape the wires to the wall with painter’s tape so they don’t fall in the hole while you prepare your new thermostat.
Connect the new thermostat: Place the plate of your new thermostat against the wall where it will be located. Check the plate with a level and mark the screw holes with your pencil. Pull the wires through the opening of the thermostat’s backplate, attach the backplate to the wall with the provided screws, and reconnect the wires according to the industry standard color codes or your unit-specific notes from Step 4. Replace the thermostat cover. Turn the HVAC power back on at the main breaker.
Remember, if you are unsure about any wiring to your thermostat, contact a professional electrician for assistance.