How To Replace a Thermostat
Programmable, digital thermostats allow you to set the temperature for your home by time of day and by day of the week. This allows you to set a comfortable temperature for times when you are home, a lower temperature while are sleeping and another temperature while you are away from home. This can add up to a big savings in energy use by not heating or cooling unnecessarily. Plus, if you select the feature, you can program different schedules for different days of the week. If you need more information on selecting a thermostat, read our article.
Replacing a thermostat is surprisingly easy to do. In most cases it can be accomplished in 15 minutes with just a screwdriver. But more important is why you should consider installing a programmable digital thermostat. A new thermostat will save energy and money, all the while making your home more comfortable.
Installing a New Programmable Thermostat
Standardized Terminal Labels
for Thermostats Manufactured
in 1973 or later
- R: "Hot" side of transformer or RH for heat, RC for cool (red):
- W: Heat control (white)
- W2: Heat, second stage (pink or other color)
- Y2: Cool, second compressor stage (blue or pink)
- C or X: Common side of transformer (24 V) (black)
- Y: Compressor activity (yellow)
- G: Fan (green)
- O: Energize to cool (heat pumps) (orange)
- L: Service indicator lamp (tan, brown, gray or blue)
- X2: Heat, second stage (electric) (blue, brown, gray or tan)
- B: Energize to heat (blue or orange)
- B or X: Common side of transformer (blue, brown or black)
- E : Emergency heat relay on a heat pump (blue, pink, gray or tan)
- T: Outdoor anticipator reset (tan or gray)
Turn off the power at the circuit breaker to your furnace. Remove the cover plate to your old thermostat. It is important to note which wires are connected to which terminals. Taking a digital picture is a good idea. Disconnect the wires from the thermostat and secure them so that the wires cannot fall inside the wall. Clip the wires with a clothes pin or large paper clip is effective. Unscrew the thermostat base from the wall and remove it.
Each manufacturer's instructions will vary regarding installation. Our guide provides the general steps for installation but you should always follow the specific instructions provided with your new thermostat.
Run the wires through the base plate of the new thermostat and resecure the wires with the clothes pin. Secure the base to the wall with one screw. If you don't have a level handy, tighten it enough that it will hold the thermostat in position. Step back a few steps and determine how much to adjust it to make it level. After adjusting, step back again. If it looks good, install the other screws.
Your old thermostat should have labels for each terminal. If it was made in or after 1973, they should match the labels in your new thermostat. Simply install the wires to the matching terminals on the new thermostat.
If there is any question as to the wiring, it may be necessary to note the wire colors and then check which color is connected to what on the furnace, boiler, heat pump or air conditioning. If with that information you still cannot make a determination consult a professional or Acme's Forum for advice.
Snap the cover onto the base, turn off the heat and cooling operations on the thermostat and restore power to the system at the circuit breaker. Test the heat by turning the thermostat to "Heat" and "On" and listen for the furnace to start and check for warm air. Test the AC similarly. Note that you should not operate the AC when outdoor temperatures are below 65 degrees; limit the test to determining whether the system starts when turned on.
Now, program the thermostat with temperatures and times for operation and you re done.