Tests were performed to measure pressure losses in lightcommercialduct systems comprised of wire-wound flexibleduct and rigid sheet metal duct. The tests determined the pressureloss associated with various lengths of flexible duct usedin multi-branch systems. ASHRAE Handbook guidelinesrecommend a maximum 6 ft (1.83 m) length of flexible duct forcommercial applications. The total pressure loss penalty for asystem that utilized 11 ft (3.35 m) of flexible duct branchesconnected to diffusers was 3%, compared to a duct systemmeeting this recommendation. A system using completelengths of properly sized flexible duct yielded a total pressureloss that was 22% less than a multi-branch system whichconformed to prevailing requirements. Regarding themeasured flow imbalance in the branches, systems that usedflexible duct branch lengths greater than the existing limit of6 ft (1.83 m) exhibited negligible adverse effects.