Sounds like a fan / filter box, not a dust collector. A prop fan will work, but with loaded filters you probably have 1/2" of static, and the prop fan drops off in airflow pretty quick. An airflow rating by itself is of no use at all unless associated with a static pressure. Your "1250 CFM" is most likely "1250 CFM free air" or at 0" static. And a prop fan's curve drops off real fast at any pressure, prob'ly stalls at about 3/4".

A forward curve double-width fan out of a recycled furnace is a much better choice. But hey, if it's working for you, great! Keep the filts clean and it'll work better.

: I used an "attic exhaust fan" from Home Depot, ($35.00) with 4
: 20" X 20" furnace filters in a plywood case. Put rollers on the
: case for portability and the fan is rated at 1250 CFM air flow. Works
: great. Not sure of the name, but the idea came from one of the small shop
: books I picked up at the library. Ric