Abstract: A transition barrier for an air handling unit is provided, wherein air handling unit has at least one functional section. The air handling unit also has a cabinet that surrounds the at least one functional section. The transition barrier including a bottom panel having a bottom cutout and a top panel positioned adjacent the bottom panel and having a top cutout aligned with the bottom cutout to form a conduit reception aperture. The conduit reception aperture extending through the transition barrier and configured to receive conduit extending along the air handling unit. The transition barrier extending laterally and vertically between members of the cabinet to isolate the at least one functional section.