There are ratings for various degrees of "suction". Those should be reasonably accurate. I can say that I'm getting by with less CFM than the engineers recommended, quit a bit less.

The engineers at Stuppy wanted me to run two fans with 3/4 hp motors and one 1/2 hp. That's what I bought and set up. But changed to 1/4 hp using big fans, 36 inch. That fan with 1/4 hp is rated about 8K CFM, with 3/4 hp it's rated 12K CFM. Bigger motor triples power useage while showing 50% more CFM. That's a no brainer. Use the big fan, small motor, and 240V to move much more air per dollar spent on electricity. From what I've seen it's that simple.

A bigger inlet will help. Mine is pulled thru evap pads. That's sized to fit CFM but works very well at lower CFM IME. My pads are sized for 24,000 CFM but cool very well at 16,000 or 8,000.

This post was edited by fruitnut on Sat, Dec 6, 14 at 12:58