I've had 2 of these for the last 10 years. One of them I put in the barn, to keep the air flowing for when we bring the horses in at night. As the name says, its a commercial fan, puts out quite a bit of air, and has never squeaked despite being caked in dust at times.
http://www.kaz-canada.com/kaz/produc...nd-fan-hv-181/ if you can find one, they are worth hunting down.