Ecostat Mercury-free 1 Heat/1 Cool Non-programmable Round Thermostat, Large Easy to Use Mode Switches Push Button Backlight, Mercury Free, Soft Rubber Set Temperature Ring, Large Easy to Use Mode Switches, Easy Installation, Includes extra wallplate, mounting hardware The ES100 digital thermostat is designed to work on the following 24V systems. This thermostat will not control multistage heat pump systems or 120V line voltage heating systems. Suitable for: Gas - standing pilot , Gas - Electronic ignition , Gas - Fired Boilers , Oil - Fired Boilers, Oil - Fired Furnace Single Stage Heat Pumps with no Auxiliary Heat Electric Air Conditioning Specifications: Setpoint Range: 41-90 degrees F , Terminals: RH, RC, W, Y, G,B, O , Power: 2 AAA Alkaline Batteries (included) , Thermostat Dimensions: 3 5/8" Round, 1 3/4" Deep., System switch positions - HEAT / OFF / COOL , Fan switch positions - AUTO / FAN ON