How to Wire a House Thermostat

Keep home temperatures comfortable with an accurate thermostat.

A thermostat controls operation of the heating or cooling system based on the temperature it reads. If the unit is not sensing temperature changes accurately or relaying start and stop signals, then the home temperature will not reflect the setting. The most commonly used thermostats are battery powered switches that relay electric power to one heater and one cooling system. The electrical wiring for a home thermostat is typically color-coded for uniform installation by service technicians. Homeowners who elect to put in new thermostats can follow the wiring code for do-it-yourself installations.

Things You'll Need

• Small-slotted screwdriver
• Wire strippers

Instructions

1. Cut the power to the heating and cooling system before touching any of the thermostat wiring. Shut off the breakers for the heating and cooling system, and the air handler, or shut off the main power breaker switch to ensure that no power is running through the system. Label or lock the breaker box until work is completed.

2. Cut the exposed wire off the ends of all wires. Strip off 1/4 inch of the insulation with wire strippers. Determine the correct wire stripper gauge to use by trial and error. If the insulation does not get cut on a particular setting the chosen gauge is too large, but if the metal wire gets cut the gauge is too small.

3. Push the red wire into the opening for the home thermostat terminal labeled "RH" to bring power into the unit. Slip one end of the short red jumper wire into the RH terminal as well. Tighten the terminal screw with a small slotted screwdriver. Push the other end of the red jumper wire into the "RC" terminal to relay power to the heating, cooling and fan systems when necessary. Tighten that terminal screw firmly.

4. Push the exposed end of the green wire into the terminal marked "G" for the fan power relay. Tighten the terminal with a screwdriver.

5. Push the white wire into the "W" terminal to provide a power relay for the heater. Secure the terminal screw.

6. Push the yellow wire into the "Y" terminal to send power to the air conditioning compressor. Secure the terminal screw. Clip the face of the thermostat on over the front of the wire compartment, and set the desired system and temperature.

Tips & Warnings

• These instructions illustrate installation of a battery powered thermostat to control a single heater and a single cooling system. They do not apply to thermostats for controlling a multistage cooling system or a heat pump.

• Improper wiring will ruin a thermostat. Wire colors used for the house thermostat circuit are subject to the accuracy of the installing technician and may not reflect the standard color code established for home thermostats.

References

• Pro Thermostats: Thermostat wiring information
• High Performance HVAC: Thermostat wiring and wire colors