Construction
Duct CFM Sizing Calculator
CFM in, round metal duct diameter out. Based on ACCA Manual D friction rate of 0.08 in WC/100ft.
Round duct (in)
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- Velocity (FPM)
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- Rect. equivalent
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- Flex limit
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FAQ
Why 0.08 friction rate? +
ACCA Manual D residential default. Larger systems with long runs use 0.05; commercial uses 0.10.
Flex velocity limit? +
Flex duct velocities >600 FPM cause noise. Keep flex to short final connections only.