Your review: Just finished intalling the fan and will be connecting it to our vent system this weekend. Description was missing any referenced to variable speed controllers and had to contact manufacturer as global industrial was of no help. Was told that this unit had a sealed motor and selected it for a exhaust sytems for an acid booth since it had a plastic fan and epoxy paint. Upon recieving the system, the mfg docs say not to use in a corrosive environment (not on global industrials info) but don't define corrosive. We'll see how long it holds up. For its size, it is relatively quiet and has very low vibration (we did not use vibration isolators and it seems fine).