I bought a 20" Lasco box fan because the store said it would move 2500
cfm for 80W. If it sounds too good to be true, it probably is.
According to my measurements, it moves about 1000 cfm for 91W.
Bigger fans move more air more efficiently. I don't know why there
don't seem to be inexpensive box fans bigger than 20".
Is there a better alternative?

I'm sure you could find larger and/or more efficient fans if you're willing
to search and pay for them. However, on a simple cost basis, it would
probably be cheaper to just buy additional box fans for more airflow.

Also, keep in mind the fan can only blow "out" the air it can pull "in"
from somewhere else. If you don't have an equal sized window open in the
room, or elsewhere in the house if you leave a door open, the airflow will
be restricted. It will be pulled through cracks, around outlets, from hot
attics, or wherever the air can be pulled from.

If you have two windows, you could try placing one fan to blow air out one
window, then place the other fan to pull air in from outside.

Finally, consider the effects of having too much airflow in the room. Dry
eyes, papers blowing around, etc.

Anthony Watson
Home Cookin Recipe Software
www.mountain-software.com