Dryer exhaust | Fantech
According to some dryer installation instructions and local building codes, booster fans should be added in the dryer duct run when the length of duct exceeds 25 feet with no bends, 20 feet with one bend or 15 feet with 2 bends. With an existing system you may find that drying times are far longer than the dryer manufacturers instructions give, this may indicate that you have an duct run