How do I install a new thermostat?
Installing a programmable thermostat is one of the simplest things you can do to save energy and money in your home. You’ll save 1% 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 from prothermostats.com, 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, which should not present a shock hazard. But if the 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 with a licensed electrician. You should always use a voltmeter to check the voltage of your system.
If you’re replacing a thermostat that contains mercury in a sealed tube, don’t just throw it away. You’ll need to contact your local waste management agency for instructions for proper disposal.
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.
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.
The old thermostat should have a letter identifying each wire. Attach a label that’s included with your new thermostat to each wire that corresponds to the letter on the old thermostat. If your new thermostat does not have wiring labels, use masking tape to mark each wire with the old thermostat's corresponding terminals.
Once the wires are marked, disconnect the old thermostat – but 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.
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 that the base is straight, then mark the center of the mounting plate's screw holes.
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.
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, matching the masking-tape labels to the letters on the terminals.
Turn the electricity back on at the service panel, and test the thermostat – in both the auto and manual modes – 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 that 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.
Questions/Comments? Contact Us