I own a warehouse that needs to push 25,000 CFM. I currently have an old warehouse exhaust fan that doesn't push anywhere close to this. The diameter of the fan blade is about 36 inches, but the frame in which the fan sits is 41 x 41 inches. I've done a bit of looking and can't seem to find a fan that is 41 inches or less in diameter that pushes 25,000 or more CFM. So, I really have two questions:

  1. Does a fan exist that would push 25,000 CFM which that could fit into the 41 x 41 opening (probably means close to a 36 in diameter fan blade); and
  2. Is there a mathematical function that relates RPMs of a fan, the number of blades, and size of the blades to CFM (or a similar function such that when you plug in the size and speed of the fan, you can find the CFM)?


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    $\begingroup$ Try a fan calculator such as : bergquistcompany.com/fans-blowers/fan_law_calculator.php $\endgroup$ – Solar Mike Feb 12 '18 at 5:07
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    $\begingroup$ You can also look at : tabbcertified.org/site/public/download/index/.../… $\endgroup$ – Solar Mike Feb 12 '18 at 5:09
  • $\begingroup$ You're much better off trusting the printed ratings of commercial fans. BTW I would recommend adding a second opening and a second fan rather than trying to run a single aperture at "warp speed" . And finally, how did you arrive at your 25k CFM figure? Unless it's based on local building code, maybe it's excessive. $\endgroup$ – Carl Witthoft Feb 12 '18 at 16:08
  • $\begingroup$ On item 2, I think the short answer is "no." There are multiple other factors that would impact the amount of airflow of a given fan that would make a single mathematical equation either very narrow in scope or so specific that the number of inputs would probably negate the value of the output. For example, there are different fan blade shapes that would affect the airflow, the pitch of the fan blades would impact the airflow, and an equation like this really should probably include air density data, though you could make some assumptions there, I suppose. $\endgroup$ – Secundus Feb 18 '20 at 21:05

I did some quick math. Call the opening 3 ft sq or 9 ft^2. Dividing 25,000 ft^3 by 9 ft^2 will give you the third dimension of 2,777 ft, which would need to travel in a minute. This is about 31.5 mph wind speed. I did a quick search of measured wind speed for fans, they were approximately 4 to 8 mph. Probably not for 25,000 CFM.

  • $\begingroup$ You sir, are awesome. Thanks a million. This is exactly what I was looking for. $\endgroup$ – StatsStudent Mar 13 '18 at 19:17

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