How to Install a Programmable Thermostat

Lucky you. A hundred years ago, rich folks needed servants to rise before dawn and stoke the furnace so the house would be warm when the family got up. Now, you can adjust your home's heating and cooling with a programmable thermostat. It's affordable, automatic and, unlike servants, it won't quaff your cooking sherry or elope with the chauffeur.

Do It Yourself or Hire a Pro?
A heating contractor will charge between $100 and $120 to remove an existing thermostat and install a new programmable unit. A homeowner with basic electrical skills can do the job for $25 to $65, depending on the cost of the thermostat. The job should take a couple of hours.

Do It Yourself

Before you purchase a new thermostat, note the number and type of wires attached to your old unit. If your old thermostat is connected to thin wires coming directly out of the wall, then it has low-voltage wires, which don't present a shock hazard. But if the thermostat is wired into an electrical box, then it's probably running off 120-volt current. Don't attempt to replace it with a new thermostat without first consulting a licensed electrician.

Step by Step
1. Shut off the power. Turn off the power to the furnace and central air conditioner unit by shutting off the circuit breaker or removing the fuse at the service panel.

2. Remove the old thermostat cover. Remove the old thermostat's cover from its mounting plate, but don't disconnect any wires (see image above).

3. Remove the mounting plate. Unscrew and remove the old thermostat's mounting plate from the wall.

4. Label the existing wires. The old thermostat will have a letter identifying each wire. Attach a label (included with your new thermostat) to each wire that corresponds to the letter on the old thermostat. If no labels are provided, use masking tape (see image, left).

5. Disconnect the wires. Once the wires are marked, disconnect them from the screw terminals. To keep the wires from falling back into the wall, we like to wrap them around a pencil. If you discover an old paint color behind the mounting plate, make sure that the new thermostat will cover up the mismatched paint. If it doesn't, repaint the wall before you install the new thermostat.

6. Prep the thermostat base. Thread the wires through the base of the new thermostat. Be sure that the base sits flush against the wall and none of the wires are trapped behind it. Place a torpedo level on top of the base and adjust the base until it's perfectly level. Use a sharp pencil to mark the center of the mounting plate's screw holes.

7. Drill the mounting holes. Remove the base and drill a 3/16-inch-diameter hole at each screw location.

When you drill holes to mount the new thermostat, hold a vacuum cleaner hose up against the wall to catch the drywall dust.

8. Attach the base to the wall. Use a hammer to gently tap plastic anchors into the holes. Reposition the thermostat over the anchors. Thread the wires through the base of the new thermostat and insert the mounting screws (see image, left).

9. Level the base and tighten it to the wall. Use the torpedo level again to ensure that the base is still level. Once level, tighten the mounting screws.

10. Connect the wires. If necessary, use a wire stripper to remove about 1/4 inch of plastic insulation from the ends of the wires. Connect the wires to the screw terminals, matching the masking-tape labels to the letters on the terminals. Also, consult the wiring diagram in the installation manual to make sure everything is properly hooked up.

11. Turn on the power. Turn the electricity back on, then follow the thermostat's manual to program the unit. Finally, run a test in both the auto and manual modes to confirm that the furnace and air conditioner go on and off, as directed by the thermostat settings.

Hire a Pro
It may take more than one phone call to find an electrician who's willing to install a single thermostat it's too small a job for most but with a little persistence, you should be able to find a qualified person.

You might also consider adding a few other small electrical upgrades to the job, such as installing a new floodlight, replacing a light with a ceiling fan or adding a couple of wall outlets. A professional is more likely to take a job if there's at least a full day's work in it. Plus, you save time and money by having him or her come out just once to complete three or four simple repairs and upgrades.

CornerHardware.com recommended tools & supplies: Wire Stripper/Cutter Screwdriver Drills 3/16" Drill Bit Electrical Tape Hammer Torpedo Level