iO HVAC Controls D-Z1-2618 26 X 18 Two-Position Zone One Damper AssemblyiO HVAC Controls D Z1 2618 ACTUATORS ARE INSTALLED ON 2ND DIMENSION 26 x 18 Two Position Zone One Damper Assembly 26 x 18 Rectangular Two Position Zone One Damper Assembly, 24V 30 second actuator, Thermostat Sold Seperately, Auto Changeover, Duct Temp Sensor and actuator control board wired on damper, Stand alone damper assembly and thermostat monitor duct air temp and help maintain room temperature to maintain setpoint on thermostat. Thermostat does