How to Install a Thermostat in 3 Steps

Save money on your energy bill

Next Project

An hour or less






Save a lot of money! Learn how to remove your old thermostat and install a new programmable thermostat—with no rewiring required.

Tools Required

  • 4-in-1 screwdriver
  • Cordless drill
  • Drill bit set
  • Level

Materials Required

  • Clothespin
  • Tape
  • Wall anchors

You can reduce your home’s heating and cooling costs by about 15 percent with a programmable thermostat. It automatically keeps the temperature at a comfortable level when you’re home, but switches to an energy-saving level when you’re away or asleep. Programmable thermostats are available from home centers and hardware stores. The higher-priced models provide more programming options.

Programmable thermostats will work with most gas or oil furnaces and central air conditioners. However, heat pumps, electric baseboards, and a few other systems require special features. Read the package to make sure the programmable thermostat you buy is compatible with your heating and cooling system. If you are unsure, call your local utility or a heating and cooling contractor.

Should you get a Wi-Fi thermostat? Click here to find out more.

Project step-by-step (3)

Step 1

Remove the old thermostat

removing thermostat

To begin, turn off power to the heating and cooling systems at the main panel. Then remove the old thermostat. If your old thermostat contains mercury, you’ll see a small glass tube with a shiny silver ball inside. Mercury is toxic. Take this type of thermostat to a hazardous waste disposal site.

There will be anywhere from two to five wires hooked up to the old thermostat. Label the thermostat wiring with marking tabs using the letters on the old screw terminals as reference. If your new thermostat doesn’t come with marking tabs, use masking tape. Remove and discard the old thermostat. Here are a few things you need to know before you upgrade your thermostat

Step 2

How to Hook Up a Thermostat: Install the mounting plate

mount new thermostat

Clip a clothespin to the cable so it doesn’t slide down inside the wall cavity; then level the new mounting plate in position and mark the mounting screw holes. Drill 3/16-in. holes, insert drywall anchors and screw the plate to the wall.

If the thermostat has back-up batteries, insert them before wiring the new thermostat.

Step 3

How to Hook Up a Thermostat: Hook up the wires

install new thermostat

Screw the system wiring to the screw terminals on the new thermostat using the letter labels as reference (strip the wires back if necessary). These letters are standard; hook them up to the same terminals on the new thermostat. Snap the thermostat to the mounting plate.

The thermostat may need to be configured to your heating system. It may also come preprogrammed, but to maximize savings, set it up according to your schedule. Consult the instructions that come with the thermostat for system adjustments and programming. You won’t save energy if the thermostat isn’t programmed correctly.