A programmable thermostat offers more control options and saves on home heating and cooling expenses. It allows you to set different temperatures for different times of the day, and even different times on different days. In cold weather months, you can set it to automatically lower the temperature when you leave for work and raise it an hour before you return home. You can do the same when it comes to cooling during warm weather months. That way your furnace or air conditioner does not operate all day and waste fuel or electricity when the house is unoccupied.
Choose a thermostat that provides accurate readings -- generally about one degree from the temperatures you set. Thermostats that allow temperature swings of two to three degrees will significantly reduce your home’s efficiency and comfort.
Shut off the power to the furnace or air conditioner. Even though thermostat wires are low voltage, the furnace electronics can be damaged by a short circuit if you touch the live wires together during installation.
Detach the wires from the old thermostat. There are four wires to disconnect. Keep the disconnected wires from slipping back into the wall by temporarily wrapping them around a pencil.
Each thermostat terminal is identified by a letter, and each of the wires is a different identifying color. Note which wire goes to each letter, and write the letter on a small piece of tape attached to each wire. The wire colors may not attach to the same terminals on the new thermostat – always follow the letter code.
Mount the new wall plate. If the screw holes don’t line up with the existing mounting plate holes, mark the new locations and drill the holes, then install wall anchors if necessary for the new mounting plate.
Attach the wires to the terminal screws, matching the letters on the wires to the letters of the new unit.
Install batteries in the thermostat and snap the cover in place.
Follow the manufacturer's instructions for programming the new thermostat. The basic temperature settings are the same, but the new unit will allow you to set multiple times for turning the heating or cooling on and off. For example, you can set a workweek schedule and a weekend schedule, as well as a night set-back time.