Return to the Heating & Air Conditioning Forum | Post a Follow-Up

CFM For 12 in duct

Posted by JoeK321 (My Page) on
Wed, Mar 21, 12 at 23:10

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?

Follow-Up Postings:

RE: CFM For 12 in duct

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.

RE: CFM For 12 in duct


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.

RE: CFM For 12 in duct

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

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here