This guideline covers the application of mixed air control dampers in air-handling units and systems that incorporate air-side economizer systems for cooling. This guideline addresses the selection of control dampers based on damper characteristics and damper pressure drop. This guideline is not intended to cover dampers used elsewhere in heating@ ventilating@ and air-conditioning (HVAC) systems. This guideline does not cover air mixing. PURPOSE This guideline provides the basis for selecting and sizing control dampers (outdoor@ return@ and relief) commonly found in constant-air-volume (CAV) and variable-air-volume (VAV) air-handling units (AHU) and systems with air-side economizers.