Installing a programmable thermostat

In this report: Overview

Installing a programmable thermostat

Last reviewed: August 2009

Replacing a standard thermostat is a simple job that will save you money. All you need is a screwdriver, a drill, and 5 or 10 minutes. Read our buying advice on programmable thermostats to find the models that are easiest to use and can save you money off your heating and cooling bills.

Start by popping off the cover to expose a couple of screws that you back out to remove the body of the thermostat from the wall. A few more screws hold wires that run to the furnace. If the thermostat controls the heat supply and nothing else, there will be only two wires; if it also controls a central air conditioner, there'll be more. Knowing which goes where on the new thermostat is straightforward--the wires are color-coded, and the screws in programmable thermostats are labeled.

You will probably need to drill new mounting holes for the thermostat. Screws are usually included with the thermostat, along with plastic anchors that will help hold them in the drywall. Our buyer's guide to cordless drills can help you choose the right model for you needs.

Note that the thin low-voltage wires connecting most thermostats are relatively safe to work with. But full household current may run through a thermostat that governs electric baseboard heaters, and only an electrician or an HVAC contractor should handle replacement of those.

Step-by-step instructions

Take the cover off the old thermostat

Turn off the power supply to the existing thermostat at the home's circuit breaker, at the fuse box, or at the furnace cutoff switch, if there is one. If the thermostat is on an electric baseboard heater, hire an electrician or an HVAC contractor instead of doing the job yourself.

Remove the wires

Unscrew the wires from their terminals. If the wires aren't color-coded, label them with tape, marking each piece with the letter of the nearby screw terminal.

Unscrew the mounting screws

Remove the screws holding the body of the thermostat to the wall, and take it off the wall. The wires will sometimes try to slide back through the hole in the wall that they pass through; if so, tape them temporarily in place.

Lay out holes for the new thermostat

Put the template that comes with the new thermostat on the wall. Poke a pencil through the marks on the template to show where on the wall the screws should go.

Drill holes for anchors

The package will include small plastic anchors that you put in the holes to help hold the screws in place. You won't need them if you happen to drill into a stud. Drill holes in the wall for the anchors--the package directions will tell you what size holes to drill.

Put the anchors in the wall

Push the anchors into the holes. Plaster and drywall are fragile, and without the anchors or a stud behind, the thermostat would come loose with normal use.

Screw the thermostat to the wall

Feed the wires through the opening for them in the body of the thermostat. Screw the body to the wall, driving the screws into the plastic anchors, or the studs.