No, anything you do to the fans will decrease the cfm's: e.g. ducting, square to round adapters, too much/too little spacing between the fans, etc. I have a 130cfm fan (4" round) exhausting the heat from my 2x2x4' box (16 cu ft) through a 90 degree bend, 4"-3" reducer and 6' of 3" flexduct (what I had) into the attic and it keeps it perfect. You really don't want to go lower than 100cfm at the minimum, I had to play around with 3 different fans to get this result.