How to Install a Thermostat in 7 Steps

Turn off the power to your heating and cooling system at the breaker before you touch anything. Thermostat wires are low voltage but it is not worth the risk.

Once the power is off, snap a clear photo of the existing wiring with your phone. This photo is your reference for the new wire-by-color matchup later. If your old thermostat is mercury-based, set it aside for proper hazardous waste disposal.

Most modern thermostats clip onto a base plate with a pin connector plus four corner clips. To remove yours, tilt the face plate forward and pull it straight off the base. The wires stay attached to the base plate at this stage - we will deal with them next.

Stick a small label on each wire matching its terminal letter from the old base plate. Green wire goes to a sticker labeled G, red to R, white to W, yellow to Y, and so on. This is the step that makes the new install foolproof - you will match each labeled wire to the same letter on the new base plate.

Before you remove the old base plate, clamp a set of vice grip pliers across all the wires below the base plate. This is the most important trick in the whole job - the pliers keep the wires from disappearing back into the wall when you pull the base off. Lay the pliers flat against the wall so they hang from the wires like a stopper.

With the vice grips holding the wires, unscrew the old base plate from the wall and slide it off the wires from the bottom up. Hold the new base plate against the wall in the desired position and mark the anchor holes. Tape a strip of blue painter's tape directly below where you will drill - this catches the drywall dust so it does not coat your floor.

Drill the holes, tap drywall anchors into place with the butt of your screwdriver or a hammer, and you are ready to mount.

Feed the new base plate over the wires - you may need to trim back a small amount of insulation. Loosen each terminal screw with a precision screwdriver, slide the matching labeled wire into its slot, and tighten the screw down. Blue goes to B, G to G, yellow to Y, white to W, red to R. Once every labeled wire is secured, remove the vice grip pliers.

Pop in the two AA batteries that came with the thermostat. Find the fuel switch on the back of the face plate and slide it to Gas/Oil or Electric depending on your system. Press the face plate firmly onto the tabs of the base plate until it clicks into place.

The display will light up asking you to set the time. Use the up and down arrows, hit the Run button, and your new thermostat is live. Last thing: set the system switch to Heat, Off, or Cool, and set the Fan switch to Auto.