We are going to help you understand more about the C-wire—and what you need to know before you buy or install a smart Wi-Fi thermostat in your home Standard Honeywell Thermostat - Line ...

Resideo, which makes Honeywell Home thermostats, recommends trying to turn the system ... If your system already has a C-wire, you can skip this step. If it doesn’t, you might need to add another wire ...