I had ordered both the 16" & 20" Exhaust Fans. Both work as they are supposed to. I would highly recommend these fans to anyone. If I need to buy more I will.
If you are wondering why I bought 2 different size fans, it's because my plan was to put the 16" fan at one end of the greenhouse and then put my 20" shutter at the opposite end. Needless to say I needed another fan and since my shuttler opening was already framed in I went with the 20" fan in its place.