Ask This Old House plumbing and heating expert Richard Trethewey replaces an old thermostat with a smart thermostat without replacing the original two wires in the wall.

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Time: 23 hours
Cost: $300
Skill Level: Difficult

Tools List for Upgrading a Smart Thermostat:
Drill driver [https://amzn.to/2RNofUq]
Small flathead screwdriver [https://amzn.to/36N95Cy]

Shopping List:
Smart thermostat [https://amzn.to/2tcUF0S]
Thermostat wire [https://amzn.to/31kxP4g]

Steps:
1. Start by turning off the service switch at the furnace.
2. Remove the old thermostat.
a. Pull off the front cover.
b. Unscrew the screws inside.
c. Disconnect the wires.
d. Pull off the back cover.
3. Mount the hub in a convenient location near the furnace using a drill and a few screws.
4. Disconnect the wiring from the thermostat to the furnace and run that wiring to the hub. There’s an obvious place on the hub to screw the wires in properly.
5. Run the thermostat wire from the furnace to the hub. The red wire goes to R, the white wire goes to W, and the blue wire (common wire) goes to C.
6. Mount the new thermostat back cover at the location of the old one. This might require drilling for new screws.
7. Using the old two wires, wire the new thermostat and connect it to the back cover.
8. Turn the service switch back on at the furnace.
9. Download the smart app and program it to the thermostat following the manufacturer’s instructions.

Resources:
Richard installed the InvitaTM Wifi Thermostat 564, which is manufactured by Tekmar Controls (http://www.tekmarcontrols.com/).

About Ask This Old House TV:
From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. Ask This Old House helps you protect and preserve your greatest investment—your home.

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How to Upgrade to a Smart Thermostat without Changing the Wiring | Ask This Old House
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