Try this one.
http://www.heathdiesel.com/P/HDP1039/That ought to cool just about anything!
I have not checked out the statements in this article but like anything there are formulas and constraints to take into account.
http://www.impalas.net/forums/showthread.php?t=2332We heat with wood, and I can state with certainty that the 21" fan moves more air than the 2 x 12" fan to move air out of the sunroom into the rest of the house. That is even without the advantage of a shroud for the stand fan. The 2 x 12" is a window fan that the sash sets against, making a shroud. The stand fan sits a couple of feet behind the same size window on the opposite side of the room. There is a door exactly between for intake air.
