Honeywell Hydronic Programmable Thermostat, Series: T6 Pro, +/-1 deg F Differential, Relay Switch, Heat/Off System Switching, Floor Sensor, 3 Stage, 20 to 30 VAC, 5 to 90% RH Non-Condensing Humidity, Large Display/Soft Key Controls Display, Battery/Hardwired Power Source, UWP Mounting, White, 4-1/16 in L x 4-1/16 in W x 1-3/32 in D Dimensions