what is a c wire on a thermostat

A C-wire, or common wire, is a wire that provides continuous power to a thermostat from a low voltage heating system (24v) . It is necessary for most smart thermostats that require constant power to function properly. The C-wire is usually blue and connected to the "C" terminal on the thermostat. Unlike other wires connected to the thermostat, the C-wire does not control heating or cooling functions, it only provides constant power to the thermostat. If youre installing a new thermostat and your existing one is missing a C-wire, you have a few options. You can check if there is an unused wire that can be used as a C-wire, or use a C-wire adapter. It's important to ensure proper wiring as needed for your HVAC system and corresponding thermostat (with or without a C-wire) .