I use an S&P TD100x inline fan(4") rated 130CFM, knocks the temp of my box down from 115 to 80. My box is 2'x2'x4'tall. Look around the forums and local grow shops, there's some great brands, but make sure to remember to go big or go home lol. You can always get a fan that's larger than you require and put it on a fan speed controller to keep it quieter. Basically inline fans are quieter than blowers but more expensive for the same CFM rating.