DuctFpm · hvac thermal
DuctFpm duct velocity fpm
Check whether a duct diameter keeps velocity in a target band for noise and pressure screening
Result
A=π(d/12/2)²; V_fpm=CFM/A
How to use this estimate
Compute average air velocity in a round duct from CFM and inside diameter. How it works: A=π(d/12/2)²; V_fpm=CFM/A. Out of scope: rectangular duct equivalent; friction rate tables; fan curve matching; bathroom CFM sizing rules. This is an approximate screening estimate, not a substitute for manufacturer charts or a full engineering design. Does not certify code compliance; confirm manufacturer data where it applies.
Sources, methodology, and assumptions
Methodology
A=π(d/12/2)²; V_fpm=CFM/A
Assumptions
Uniform average velocity; Circular ID; Incompressible air screen. This is an approximate screening estimate, not a substitute for manufacturer charts or a full engineering design.
Out of scope
rectangular duct equivalent; friction rate tables; fan curve matching; bathroom CFM sizing rules
Sources
Last technically reviewed: 2026-09-11