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How To Install a Thermostat
Posted 10/10/2008

Installing a programmable thermostat is one of the simplest ways you can save energy and money in your home. Infact, save 1 percent on your heating bills for every degree it's set back over an eight-hour period!

  • Time: 15-20 minutes
  • Cost: $40 - $200 (depending on the replacement thermostat)
  • Difficulty: Easy
  • Tools: Screwdriver, wire cutters/strippers, pencil, level, drill, 3/16" drill bit

Before You Start

Before you buy a new thermostat, take a minute to check the number and type of wires attached to your old (existing) thermostat.

If your old thermostat is connected to thin wires (approx. 18 gauge) coming directly out of the wall, it is most likely a low-voltage system, shouldn't present a shock hazard. But if your thermostat is wired into an electrical box or has wires thicker than a pencil lead, then it's probably running off 120-volt current. Don't try to replace it until you've consulted a licensed electrician. You should always use a voltmeter to check the voltage of your system.

Do not throw your old thermostat in the trash if it contains a mercury switch! You'll need to contact your local waste management agency for instructions for proper disposal. Check out our article on Mercury Thermostats for more information. 

Step 1

Turn off the power to the surrounding circuit and the circuit for the furnace and air conditioner at the service panel.

Mark the fuse or breaker switch with a piece of tape to make sure no one turns the power back on while you're still working.

Step 2

When you're sure the power has been shut off, remove the old thermostat's cover from its mounting plate - but don't disconnect any wires yet. Unscrew and remove the old thermostat's mounting plate from the wall.

Your old thermostat should have a letter identifying each wire. Attach a label that's included with your new thermostat to each wire that corresponds with the letter on the old thermostat. If your new thermostat does not have wiring labels, then use masking tape to mark each wire with the old thermostat's corresponding terminals.

Step 3

Once the wires are marked go ahead and disconnect the old thermostat. - Make sure the wires don't fall back into the wall. Wrap the wires around a pencil to keep them in place.

Before you go any further, install the batteries in the new thermostat (if applicable) otherwise it won't work once you get it installed.

Step 4

Position the new thermostat base against the wall to make sure it sits flush and none of the wires are trapped behind it.

Use a small level to check the base is straight, then mark the center of the mounting plate's screw holes.

Step 5

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

Use a hammer to gently tap plastic anchors into the holes, then reposition the thermostat over the anchors.

Step 6

Thread the wires from the wall through the base of the new thermostat, then insert and tighten the mounting screws.

Connect the wires to the screw terminals according to the manufacturer's instructions, making sure to match the masking-tape labels with the letters on the terminals.

Step 7

Turn the electricity back on at the service panel and test the thermostat in both auto and manual modes. This is to confirm that the furnace and air conditioner cycle on and off at the appropriate settings.

Follow the manufacturer's instructions to program the thermostat. Keep in mind you'll need to set back the temperature for at least eight hours (either at night or while you're at work) to see a noticeable energy savings.

Please note: These "do-it-yourself" guidelines are provided as an overview and should not be used as the sole instructions for installing a thermostat. Always read and follow the manufacturer's directions.

National Trade Supply, LLC cannot be held responsible for injuries or damages resulting from these instructions.