18 inches is just fine, 20 would have been to big. Shop is 100 sq ft with a couple of small windows. In the summer it heats up with the metal roof. Needed the high velocity of the metal fan to get the air circulating quick and fast. Takes up a little too much counter or floor space to be constantly in the way, so I used a hook bolt to mount it to one of the rafters. The open design lets it draw air from all over and circulate it around. The 18 inches gives me good height clearance since I'm 6 ft. The 20 inch would have hung too low. Takes about 5 minutes to cool the place off in the middle of a 90°F + day. Dogs even like hanging out in the shed now.

Great fan for the garage or shed

Excellent outdoor fans for my doggies. Definitely moves plenty of air to keep my animals cool during these hot summer days. Very reasonably priced and will recommend just for house use as well. Well worth the price and durable

Great addition to screened porch for my dogs. Low speed generates a good flow. great purchase