Orbit 83521 Clear Comfort Programmable Thermostat with Large, Easy-to-Read Display Beautiful and contemporary design complements any dcor, with large display and warm backlight for easy viewing even from across the room Early start mode ensures the desired temperature is reached by the programmed time, making for a comfortable home whenever you need it 7-Day programmability: program each day individually with up to 4 programming periods. This thermostat is not compatible with base board heaters (or other line voltage heating), multi-stage heating or cooling systems, or 3-wire hydronic systems Copy feature (from day to day), as well as permanent and temporary hold mode, reduces programming time and makes it easy to use Accurate temperature readings - to +/- 1 degree in Fahrenheit and Celsius - for ultimate consistent control One-stage thermostat that works with gas, oil or electric furnaces, central air conditioners, 2 wire hot water systems, millivolt systems, central heating and cooling systems, and heat pumps without auxiliary/backup heat.