How to Install a Thermostat

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. How to Install a Thermostat - Step 2
3Remove the mounting plate. Unscrew and remove the old thermostat’s mounting plate from the wall. How to Install a Thermostat - Step 3
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. How to Install a Thermostat - Step 4
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.
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. How to Install a Thermostat - Step 6
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. How to Install a Thermostat - Step 7
8 Attach the base to the wall. Use a hammer to gently tap plastic anchors into the holes. Re-position the thermostat over the anchors. Thread the wires through the base of the new thermostat and insert the mounting screws. How to Install a Thermostat - Step 8
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.
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. How to Install a Thermostat - Step 10
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.