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How to Install an Energy-Saving Programmable Thermostat

Save on your energy bill with controls that automatically change the temperature settings

Q: I'd like to put in a new programmable thermostat to better control my energy costs. Can I install it myself?

—Sam Aleksy, Chicago

Lance Marques, HVAC contractor, Swezey Fuel Co., replies: Sure you can. Upgrading to a thermostat that automatically changes the indoor temperature setting is fairly easy, and it can trim about $180 off your annual heating and cooling costs, according to the EPA.

Simple models that only control heat are sold at home centers for around $25. More expensive products, such as the Honeywell Prestige that I installed here, handle many more functions, including cooling and humidifying. Typically they're purchased through and installed by HVAC contractors, but you can also buy them online.

Before you buy a replacement thermostat, however, take a peek at your existing wiring. If there are only two wires, the simplest solution is to get a replacement with a battery-powered display. Full-featured devices like the Prestige need power from a third wire, something best installed by an HVAC or electrical contractor.

Step 1

Remove the Old Thermostat

Photo by Ryan Benyi

Cut off power to the furnace using the emergency shutoff or breaker switch, then unscrew the thermostat's mounting bracket. As you disconnect each wire from its terminal, label the wire with the letter of the terminal it came from. Tape the wires to the wall so that you don't lose them. Some older thermostats contain mercury; for information on proper disposal, go to the Thermostat Recycling Corporation.

Step 2

Connect the New Thermostat

Photo by Ryan Benyi

Line up the new bracket with the hole in the wall, and connect the wires to the terminals on the bracket, following the diagram in the instructions. This thermostat needs at least three low-voltage wires: a black one and a white one, which turn the furnace off and on, and one that powers the thermostat. If you have only two wires, call an electrician or HVAC contractor to run the additional 18- or 22-gauge wire.

Step 3

Connect to the Furnace

Photo by Ryan Benyi

Let your contractor hook up the new wire to the furnace and turn on the furnace's power. Now snap the thermostat's face onto the bracket. When it lights up, follow the prompts to set the temperatures you want the house to be when you wake up, leave for work, return home, and go to bed.

Step 4

Mount the Outdoor Sensor

Photo by Ryan Benyi

This wireless, battery-powered device allows the thermostat to display outside temperatures. Turn it on while standing next to the thermostat. When both units establish a connection, place the sensor in a bracket mounted on the north side of the house, above the snow line.

Is your home protected against unexpected repair needs? If not, consider investing in a home warranty.