PENTHOUSES PENTHOUSE CLOSED CORNERS (< 25 000 CFM) PENTHOUSE CLOSED CORNERS (25 000 – 60 000 CFM) PENTHOUSE CLOSED CORNERS (> 60 000 CFM) PENTHOUSE MITERED CORNERS (< 25 000 CFM) PENTHOUSE MITERED CORNERS (25 000 – 60 000 CFM) PENTHOUSE MITERED CORNERS (> 60 000 CFM)