This paper is based on findings resulting from ASHRAE Research Project RP-1333.

A study was conducted to measure air pressure loss in nonmetallic flexible ducts and included 12” (305 mm), 14” (356 mm) and 16” (406 mm) diameter ducts on a flat surface and also positioned over joists on 24” (610 mm) centers. For this study, flexible duct compression configurations were fully stretched and 4%, 15%, 30% and 45% compressed. Measurements were performed at each compression. All tests were performed in conformance to ASHRAE 120-1999, Methods of Testing to Determine Flow Resistance of HVAC Air Ducts and Fittings (ASHRAE 1999) with a positive pressure, blowthrough configuration. The data from this study exhibited higher pressure loss than prior Air Conditioning Contractors of America (ACCA) or ASHRAE data. Measured pressure losses were 2 to 13 times higher than round steel ducts.

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