How to Install a Programmable Thermostat

Programmable thermostat

Do It Yourself or Hire a Pro?
If you hire a professional, they will charge you $100-$125 to remove your old thermostat and install a new one. You can cut your costs in half or more with a little electric know-how and a couple hours.

Do It Yourself
Old thermostat

Be sure to write down the number and wire type that is attached to your old thermostat. If it is connected to thin wires coming directly out of the wall, then they are low voltage and do not present a shock hazard. If the thermostat is connected to an electrical box, it is likely running off a 120-volt current and you should contact a licensed electrician.

Step by Step
1. Turn the power off. Turn off the power to the furnace and central air conditioner unit by shutting off the circuit breaker or removing the fuse at the service panel.

2. Remove the old thermostat cover. Without disconnecting any wires, remove the thermostat cover from the mounting plate (see image above).

Remove old wallplate

3. Remove the mounting plate. Unscrew and remove the old thermostat's mounting plate from the wall.

Label existing wires

4. Label the existing wires. The old thermostat will have a letter identifying each wire. Attach a label (included with your new thermostat) to each wire that corresponds to the letter on the old thermostat. If no labels are provided, use masking tape (see image, left).

5. Disconnect the wires. Once the wires are marked, disconnect them from the screw terminals. To keep the wires from falling back into the wall, wrap them around a pencil. If you discover an old paint color behind the mounting plate, make sure that the new thermostat will cover up the mismatched paint. If it doesn't, repaint the wall before you install the new thermostat.

Level thermostat base

6. Prep the thermostat base. Thread the wires through the base of the new thermostat. Be sure that the base sits flush against the wall and none of the wires are trapped behind it. Place a torpedo level on top of the base and adjust the base until it's perfectly level. Use a sharp pencil to mark the center of the mounting plate's screw holes.

Drill mounting holes

7. Drill the mounting holes. Remove the base and drill a 3/16-inch-diameter hole at each screw location.

When you drill holes to mount the new thermostat, hold a vacuum cleaner hose up against the wall to catch the drywall dust.

Attach base

8. Attach the base to the wall. Use a hammer to gently tap plastic anchors into the holes. Reposition the thermostat over the anchors. Thread the wires through the base of the new thermostat and insert the mounting screws (see image, left).

9. Level the base and tighten it to the wall. Use the torpedo level again to ensure that the base is still level. Once level, tighten the mounting screws.

Connect wires

10. Connect the wires. If necessary, use a wire stripper to remove about 1/4 inch of plastic insulation from the ends of the wires. Connect the wires to the screw terminals, matching the masking-tape labels to the letters on the terminals. Also, consult the wiring diagram in the installation manual to make sure everything is properly hooked up.

Programmable thermostat

11. Turn on the power. Turn the electricity back on, then follow the thermostat's manual to program the unit. Finally, run a test in both the auto and manual modes to confirm that the furnace and air conditioner go on and off, as directed by the thermostat settings.

Hire a Pro
Some professionals may find it too small of a job to install one thermostat, however if you call around you should be able to find someone. You can always stock-pile your small electrical jobs into a larger one for a pro to take care of too.


CornerHardware.com recommended tools & supplies:

  • Thermostat

  • Wire Stripper/Cutter

  • Screwdriver

  • Drills

  • 3/16" Drill Bit

  • Electrical Tape

  • Hammer

  • Torpedo Level