Smart thermostat and no C-wire? Read this first

Many older systems lack the power wire smart thermostats need. It is usually fixable.

What the C-wire does

It gives the thermostat constant power. Without it, some models drain their batteries or reboot.

Adapter kits

Many brands include an adapter that adds power at the furnace.

Check before you buy

Take a photo of the wires behind your old thermostat and send it with your estimate request.

Sample article for the demo.