CFM For 12 in duct

JoeK321March 21, 2012

I have been looking at this inline fan, FKD Series Round Inline Mixed Flow Centrifugal Fan, 12" Duct, model FKD12XL.

The company says this fan moves 2016 cfm of air, but I thought the max cfm going through a 12 in duct was in the neighborhood of 700-900 cfm. What am I missing?

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The rule of thumb for a 12 inch duct is 715 cfm. You would need a 20 inch duct to handle 2000 cfm.

I assume you would either buy and fabricate a bracket that would allow you to install it inside a 20 inch duct.

Why are you tying to accomplish? Booster fans usually can't overcome a poor duct design.

    Bookmark   March 23, 2012 at 9:55AM
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Are you not talking about 715 cfm being max in a HVAC application?

Looking at the fan identified in the OP it is a whole building or space exhaust/supply device - 715 cfm is not a limit in that case.

No hassle, just asking.

    Bookmark   March 23, 2012 at 12:24PM
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I am going by the chart I found at the link listed below (see lower right hand corner). I believe the sizes are calculated for a friction rate of 0.1 wc or less.

I assumed this was for an HVAC application. If the application can allow more friction, then the air flow can be higher.

I would think squeezing 2000 cfm of air through a 12 inch duct is very noisy.

Here is a link that might be useful: Rules of Thumb for Duct Systems

    Bookmark   March 23, 2012 at 2:00PM
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