The C wire ("common" wire) is the wire that provides continuous power to your thermostat. Older thermostats didn't really need it because of them...The C-Wire, or “common wire” enables the continuous flow of 24 VAC power to ... If your current thermostat didn't need a C-wire, it (or a wire that can be used as ...Lux Geo WiFi Thermostat · Is your wiring compatible with ... · Ecobee3 lite. If you want a smart thermostat, but do not want to hassle with a c-wire, here are the top options worth considering for your home. The common wire is the low-voltage power wire that WiFi thermostats require in ... do not have a C-wire, you will need to use the Power Extender Kit (the PEK).