An Air Handling Unit is Equipment that includes a fan or blower, heating and/or Cooling coils, regulator controls, Condensate drain pans, and air filters.

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Other /More definition:
An Air Handling Unit is a type of heating and/or cooling distribution that channels warm or cool air to different parts of a building. Equipment includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters. Does not include ductwork, registers or grilles, or boilers and chillers.