I just thought that I would make a review of my vent fan by Heng. Here is where I bought it. https://www.amazon.com/gp/product/B00AP ... UTF8&psc=1
It has 3 forward speeds and two reverse. On high it moves 188 CFM of air. I usually use it on low. It is quiet, but not as quiet as the computer fan that I had been using. It changes the air in my 7 by 16 cargo trailer in a matter of minutes.
For me it has been a very nice, reasonably priced vent fan.