- Turn off the power to the furnace system at the home's primary fuse box or breaker panel.
- Remove the existing thermostat, if applicable. Apply a small piece of masking tape to each wire to mark the terminal letter designation as they are being disconnected. Typically, there will be a white wire, a red wire, a black wire and a black-striped or green wire.
- Mount the Honeywell T87 thermostat according to the manufacturer's printed instructions, with the thermostat wires fed through the center opening in the thermostat wall mount bracket. The thermostat body should be detached from the mounting bracket until the wiring connections are complete.
- Strip about 1/2 inch of the wire insulation from each of the thermostat wires, if applicable, using a utility knife.
- Attach each of the thermostat wires to the corresponding terminals by loosening the terminal screw, using a screwdriver. Next, hook the wire end clockwise over the screw and tighten it until snug. The common configuration has the white wire connecting to the "Y" terminal, the red wire to the "R" terminal, the black wire to the "G" terminal and the black-striped or green wire to the "W" terminal.
- Complete the installation by securing the thermostat body to the wall mount according to the printed instructions. Make sure the mounting bracket is secured in a level alignment to ensure proper functioning of the thermostat.
- Restore the power to the furnace system at your home's primary fuse box or breaker panel. Set the thermostat's dial to the desired room temperature and the cool-heat and fan switches to the appropriate positions.
Things You Will Need
- Phillips screwdriver
- Masking tape
- Utility knife
- The thermostat wire connections can be verified at the furnace control panel, which is usually located on the front of the furnace unit. The terminal wire connections to the furnace control are labeled with the same letters as the thermostat.