Continuing the discussion from Student Discussion: The 2021 International Residential Code® (IRC®) Exam Study Course: What is the maximum permitted length of a clothes dryer exhaust duct? How does the presence of one or more bends affect the allowable length?
Per IRC 2021 Section M1502.4.5.1, the maximum length of a clothes dryer exhaust duct is 35 feet measured from the dryer location to the outlet terminal, though this is based on a straight run with no bends. For each 90-degree elbow, the maximum allowable length must be reduced by 5 feet, and for each 45-degree elbow, it must be reduced by 2.5 feet — so a duct run with several bends can end up significantly shorter than the base 35-foot maximum once those deductions are applied.