Duct Sizing

Round and rectangular duct size from CFM and friction rate.

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Formula and source

Equal-friction or static-regain method per ACCA Manual D 3rd ed. and ASHRAE Fundamentals duct chapter. Friction rate 0.08–0.10 in WC per 100 ft typical for residential systems.

ACCA Manual D, 3rd edition by name. ASHRAE Handbook (Fundamentals) by name.

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