You’ve purchased a new thermostat and want to install it yourself. But you are not sure what the function of the blue wire in the wall is and where it should be connected to the thermostat. Blue wires are common wires and are also called C-wires. Their function is to link the thermostat to the HVAC system control panel. The wire connects the thermostat to the low-voltage heating system. On a 4-wire thermostat, the blue wire can be connected to the Y terminal instead of the C terminal. Blue wire on a thermostat (source: Reddit) In this article, I’ll explain the function of blue wires in more detail and provide some tips on how to determine whether your home is equipped with a blue C-wire. Blue wires and their function Let me start with my explanation at the beginning – the normal function of a blue wire. Blue wires are…