If you are replacing a 6-wire thermostat, you probably have a two-stage heating or cooling system in your home. A two-stage system has a high and low setting designed to maintain a consistent temperature and save energy. The first five wires on your thermostat are common to most systems, while the sixth wire will be connected to the second-stage function of either your furnace or air conditioning compressor. Install a new digital thermostat, rated for a 6-wire, second-stage system, and maximize the efficiency of your heating or cooling system.
Determine whether you have a two-stage heating or cooling system.
Turn off the power to the thermostat at the circuit breaker or fuse box. Check that the power is off with a voltage detector.
Remove the old thermostat cover, and remove the mount screws that secure its base to the wall.
Pull the old thermostat out from the wall and detach the wires, making note of which terminal letter corresponds with each wire. Bunch the wires together and tie the bunch to a pencil with a piece of twine. The pencil will keep the wires from sliding back inside the wall.
Attach the new digital thermostat to the wall. Drill holes for the base and secure it with dry wall anchors and the included screws. Make sure the thermostat fits the base properly before attaching the wires.
Attach each wire to the corresponding terminal on the back of the digital thermostat.
Fit the thermostat in the base. Turn the power back on at the circuit breaker or fuse box. Program the new thermostat according to the owner's manual.