For use with central gas, oil, electric furnaces and air conditioning. Works with millivolt systems. For heat pumps with our without aux heat. Digital 2Heat/1Cool. Easy to read green backlit display. Precise temperature control of /- 1 F (degree fahrenheit). Green backlight. Early start function adjusts the pre-heating/cooling. Basic operation keeps programming simple, and installation requires 15 minutes or less. Includes mounting hardware.