How old is your house? If you have an heat only and an old mercury thermostats it is unlikely you have C wire. To check you need to remove the cover of whatever thermostat you have and look at the wires - it will say C wire. If you don't have one google your options. Electrician can install C wire. If you have C wire easy to install this thermostat and it works great. If not electrician my use honeywell vision 8000 pro.