Things You'll Need
3/16-inch drill bit for drywall or 7/32-inch bit for plaster
Marker or pen
The Honeywell CT87N is one of the models in the trademark analog-dial Honeywell "Round" series that is often installed by homeowners and contractors for reliable, simple climate control. This particular model controls your furnace and air conditioner. It is compatible with systems that include between four and six power and control wires. You wire the CT87N by connecting the wires of the system to the terminals of the thermostat. It is crucial to match the letter codes of the system wires with the matching codes on the terminals of your Honeywell CT87N.
Turn off the circuit breakers or remove the fuses that control electrical power to your furnace and your air conditioner.
Remove the front cover and the mechanism of your old thermostat. Dispose of the thermostat according to local waste regulations for mercury if it has a mercury thermometer tube or is marked with a mercury warning.
Attach a small piece of masking tape to each wire and mark it with the letter of the terminal to which it is attached on the base plate of your old thermostat. Disregard the color of each wire and mark them only according to the letter embossed on your old wall plate. Disconnect each wire one by one.
Remove the base plate. Bend the wires over the gap in the wall left by the old thermostat so they do not fall behind the wall.
Thread the wires through the rectangular opening in the base of your new Honeywell CT87N thermostat. Align the thermostat with the wall and use a level to position it, if desired. Mark the positions of both screw mounting holes at the sides of the base plate. Remove the thermostat and be careful not to let the wires fall behind the wall.
Drill holes at the marked points and use a hammer to tap a (provided) plastic anchor into each hole. Pull all wires through the cover plate if you are using one and then through the rectangular opening at the bottom of the thermostat base.
Line the mounting holes up with the anchors and screw each mounting screw firmly into its anchor.
Match the letter(s) you marked on the tape label of any one of the wires with the corresponding letter embossed on the left side of the left terminal block or the right side of the right terminal block.
Insert any wire marked "R," "RH," "4" or "V" into the "R" terminal, any "G" or "F" wire into the "G" terminal, any "W," "W1" or "H" wire into the the "W" terminal and any "Y," "Y1" or "M" wire into the "Y" terminal. If you have a wire for both the "R" and "Rc" terminals, unscrew both terminal screws and remove the metal jumper connecting them before you insert either wire. Do not use the C or X wire at all. If you have a heat pump and both an "O" and "B" wire, do not connect the "B" wire. Cover the exposed end of all unused wires with electrical tape and push them behind the wall.
Unscrew the terminal screw, insert the exposed end of the wire firmly into the terminal slot, and tighten the screw. Tug on the wire and make sure it does not come out of the slot. If it does, repeat this step.
Repeat Steps 8 and 10 for each remaining wire.
Set the fan switch in the center of the thermostat base to "E" if you have a heat pump or electrical heating system. Move the positions of the two cycle rate switches according to the settings for your type of system. Align the tabs at the bottom of the thermostat cover with the lugs in the base and snap the cover into place.
Restore power to your system and set the dial, heating/cooling switch and fan switch as you wish.
John DeMerceau is an American expatriate entrepreneur, marketing analyst and Web developer. He now lives and works in southeast Asia, where he creates websites and branding/marketing reports for international clients. DeMerceau graduated from Columbia University with a Bachelor of Arts in history.