This one-piece Honeywell digital non-programmable thermostat features advanced temperature monitoring to minimize temperature swings ensuring your complete comfort. The RTH5100B has a green backlight and easy soft touch key operation. This thermostat also keeps the temperature settings in case of a power outage. Simple peace of mind and total home comfort. Works on all central heating and cooling systems including heat pumps without auxiliary heat source.Dimensions: 4.5" wide x 3" high x 1" deepPrecise Temperature Control of + / - 1 Degrees F for Consistent ComfortSet Point is Retained in Memory in the Event of a Power Outage