That fan is more likely a 1200-1400 cfm fan if it came off a 3 1/2 ton
system. It should make a pretty good air filter for a workshop, but locate
it where the output won't blow in your direction or working may feel a bit
uncomfortable. Your design needs to make provision for several filters, a
mesh pre-filter followed by one or two of the newer paper sub micron type
filters

--
Charley

"Peter Wells" wrote in message
...
I've a motor/fan assembly from an old air handler ( off a 3 1/2 ton AC,
ballpark 300 cfm), it was working when it came out. The plan is to make
an
air cleaner to reduce dust in the workshop by putting hte fan in a box
with
a filter on the intake. When running as an air handler it took a 20 * 20
in
filter; I'll stick with the same. Am I wasting my time, any tips before I
start?

TIA

Peter