For more information, please refer to the ASHRAE Handbook-Fundamentals chapter, Duct Design. For either type of duct, the friction factor was determined using the Colebrook equation. Pressure loss per unit length through a round sheet metal duct or a wire-wound flexible duct was calculated using the Darcy equation. One side of the wheel uses Inch-Pound (I-P) units the other side uses International System (SI) units. Refer to the corresponding field on the wheel to read flexible duct size required to maintain equivalent airflow and same pressure loss for a given metal duct size. Includes sizing for metal ducts, and for flexible duct when compressed at 4%, 15%, and 30% straight line compression. The Duct Size Calculator is intended for use as a quick reference tool for approximating duct sizes and equivalent sizes of sheet metal duct versus flexible duct.
