iO HVAC Controls D-Z1-2018-BM 20 X 18 Two-Position Zone One Damper Assembly - Bottom MountiO HVAC Controls D Z1 2018 BM ACTUATORS ARE INSTALLED ON 2ND DIMENSION 20 x 18 Two Position Zone One Damper Assembly Bottom Mount Zone One is a control damper assembly designed to solve over heating and over cooling problems. It can be used to control a single room, or by using multiple dampers to zone multiple rooms. Zone One is available as two position or modulating and with a damper. The UT32 Titan Thermostat must be ordered separately. Additional