York S1-THEH21NY is a battery/system-powered thermostat with 2-heat and 1-cool stages that offer basic operation of HVAC equipment. 2-stage heat, 1-stage cool for use with gas/electric, heat pump or hydronic heating. Works with two AA batteries/ 24-volt system power. Auxilliary heat indicator. Easy to operate with large LCD display. Fahrenheit or celsius temperature indicator.