Don't let an old thermostat suck the energy (literally!) out of your home. Upgrade to a smart, easy-to-program, and energy-efficient thermostat. They're easier to install than you might think, and many models pay for themselves after a year.
Before you buy a smart thermostat, make sure your home's heating and cooling system is compatible with it. Also be sure to download the thermostat's mobile app (if available) so you can track your usage, set your thermostat on the go, and learn how to use less energy.
Turn off power at the circuit breaker for your heating and cooling system. If the system is running, wait until it stops. Then drastically adjust the temperature. If you don't hear the air kick on, then you know it's off.
Snap off or unscrew the existing thermostat cover. Take a picture of the wires with a camera or smartphone to remember how your system is laid out.
Use small stickers (the Nest comes with labeled stickers) or pieces of colored tape to label each wire. Then disconnect the old thermostat backplate with a screwdriver.
Unless your new thermostat is the same shape and size as the old one, you'll likely need to patch the wall. Spread joint compound onto the wall with a putty knife. Let dry. Lightly sand the area, then paint to match the existing wall shade. Let dry.
Thread the wires through the backplate of the new thermostat. Attach backplate to wall with screws. If desired, predrill the holes.
Insert each labeled wire into its matching connector. Push the wires in until they click. Once all wires are attached, push them flat against the wall to make room for the thermostat display plate.
Attach the thermostat display plate to the backplate. You should hear it snap securely into place.
Turn the power back on at circuit breaker. Then program the thermostat according to manufacturer's instructions. A smart thermostat will learn your habits and sync to your mobile phone, allowing you to adjust your home's temperature at any point and saving you money on energy bills.