Can't remember the name of the one that I put in but ours runs 30 feet plus 3 90's and 2 - 45's.  Not a problem at all.  I ended up wiring an outlet for the fan unit by sensing current draw on dryer circuit and then turns on power to outlet.  They make ones that can sense airflow but this is a more exact design that I liked.  I think there are some cheap ones that can get plugged with lint easier.  

Edit - found website
http://tjernlund.com/dryer_booster.htm