Aube by Honeywell TH135-01-B/U Hydronic Heating Non-programmable Thermostat Compatible with hydronic floor heating and central heating; also compatible with electric heat applications using a relay (see accessories) 2-Ampere (inductive) 24-Volt R, W Millivolt compatible Remote input enables change of temperature modes by phone (Telephone controller required - Aube by Honeywell CT240) Low battery indicator gives 60-day warning to replace battery (2 'AA' batteries required) Dimensions (height by width by depth): 3.1-Inch by 3.1-Inch by 0.8-Inch