Abstract: A damper assembly adapted to be affixed to an air-handling unit at an installation site including a plurality of adjacent damper assembly units adapted to be mounted with and for regulating air flow from the air-handling unit, the damper assembly unit having an interlocking structure for interlocking adjacent damper assembly units theretogether. Further, the damper assembly has a damper structure for simultaneously and independently controlling the relative mixing proportions of heated air and cooled air with ambient air for use with a multi-zone air-handling unit.