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duct sizing for 4000 to 8000 cfm?

I can google duct sizing, and see 20" diameter metal round duct for 2000 cfm,
and a 42x12 rectangular duct for 3050cfm.

I am interested in ballpark duct sizing for the 4000-8000cfm range?

And how much cfm would a 42 x 42 inch rectangular duct accommodate?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,177
    edited August 23
    Depends on the velocity and things like static pressure. Is this for HVAC or is this a wind tunnel for testing airfoils of some sort?
    At .1 static pressure

    At .01 static pressure.

    At .01 Static pressure but a much longer duct

    So how powerful is the fan that is driving that air? How long is that duct? Are you using interior insulation? is it smooth metal interior?
    Try it yourself

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org