This does require a "C" wire to operate. The "C" brings power to the place the thermostat is mounted to the wall and this does need that power. If there isn't one on your current thermostat it isn't hard to get one there usually. There are usually 1 to 2 extra wires on the bundle behind your current thermostat. One of those can be hooked up on the control board "C" terminal and now you have a "C" wire at the wall mount location. As long as your system is a usual 24V system. If you're not sure then you should have your HVAC company look at it and let you know. If you're installing wires yourself heed the warning to turn off the breaker at the main panel while working. There is usually not enough power to electrocute you but you can easily short out the main circuit board on your system. Even with all the precautions check your wires. I didn't see it and the insulation was split on one wire at the thermostat and blew a fuse when I turned the power back on. Luckily that was an easy fix but it could run into a couple of hundred dollars if you fry the board! Good Luck!