Question....my friend has a 6" 409 cfm fan but running 4" ducting. Also has a 8"x6"cored, 24" long DIY carbon filter reduced to fit the 4" ducting. How hard will this be on the fan? Will it be able to pull enough through to work? The area is 2.5x2.5x7' with a 400hps. 2 3" passive intake holes from a room with a/c. Plans on running 3-4 plants from Sannie's. Any input would be greatly appreciated.