I would go with the 6inch fan to be safe. Better to have to much air moving than not enough. What brand fan are you thinking of purchasing? I went with a cheap Amazon fan (8inch
Vivosun) and although it moves a lot of air, it vibrates my whole house and sounds like a jet plane taking off when it fires up...lol My wife says I really need to upgrade. I think I'll take the leap and get an
AC Infinity fan with the Temp and Humidity controller...that's the way to go imo. Even though now I've gotten used to the vibration and its almost...comforting. lol