FOR HEAT PUMPS AND REGULAR FURNACE A/C SYSTEMS! Mercury Free. Save up to 30$ on Energy Bills. Pre-programmed for your convenience. Heat Pump Compatible This thermostat works with heat pump systems with or without auxiliary heat. Keeps track of your filter usage. Alerts you to replace your furnace filter. Automatically switches heat-cool. Switches when the seasons change. Works with virtually any furnace including Millivolt, C-Wire, and 24-Volt Systems. It even works with Zoned systems having with multiple thermostats. It does not work with 110V/240V baseboard heaters. Supports 2 complete Programs with 2-4-6 time slots per day! Lets you program 2 complete programs to fit your busy life. Includes wall mounting plate and hardware, installation and programming instructions. Progam with ease, unit snaps off of the wall to program in any location. Remote controls require the thermostat operate on external power. A wire labeled "C" required to power this product. If you do not have a 'C' Wire the remotes with not work.