I am not an electrician. When I decided to replace my old thermostat with a programmable one, I almost backed out twice, because the thought of touching house wiring made my stomach drop. It turned out to be a forty-minute job that has cut my heating bill noticeably.

Most thermostat swaps are safe and simple, as long as you kill the power first and label the wires.

Before you start

• Turn off the power to your heating and cooling system at the breaker. This is not optional.
• Take a photo of the old wiring. You will thank yourself later.
• Label each wire with the letter printed on the old thermostat terminal.

The swap

1. Remove the old thermostat faceplate and unscrew the base.
2. Note which letter goes to which wire color. The letters matter more than the colors.
3. Connect the wires to the matching terminals on the new thermostat. The labels usually match exactly.
4. Attach the base, snap on the faceplate, and turn the power back on.

My near-miss

I forgot to label the wires and dropped the faceplate, scattering four screws. I had the photo, so I got it back together, but it took an extra twenty minutes of squinting at a phone screen. Label the wires and keep the photo open and you will be done in one try.

When to call a pro

If you see more than five wires, or a wire on a terminal labeled C with no obvious match, stop and call a professional. Heat pumps and systems with a common wire can be trickier, and guessing can damage the equipment.

After the install

Set a schedule: lower heat while you sleep and while you are at work, comfortable when you are home. Even a few degrees for a few hours a day adds up. Mine paid for itself within one winter.

I still do not love touching wiring, but now I know the thermostat swap is one of the friendlier jobs in the house.