As others have said, the speed selection between the 3 speeds suck (pun), It's their, but not a huge difference between the 3. Also, don't bother trying to follow the instructions or try using the hardware they provide, both totally suck. Go to hardware store of your choice and get construction grade 2.5 inch long screws. (you need 6 of them). Use a cheap car jack with a milk crate and a 1 by 3 wood board exactly 29.75 long and tape board across the fan so car jack has good place to support. Raise up to needed height. Then using drill, zip screws in on a slight angle outward. I had no trouble attaching the 5 screws back in place that hold the cover and I did not leave a gab in the back when mounting. Overall, I'm happy with unit, it's loud as a F-16 taking off, but it does a good job.