An external suspension system for supporting an inflatable air duct includes a series of external hangers that help hold the duct open while the duct is deflated. In some embodiments, the suspension system supports the duct at a series of points that are broadly distributed in a staggered pattern across the duct, yet the entire duct can be suspended from a single overhead cable, even if the duct is a stepped tube with multiple diameters. The system includes novel ways of locking the hangers to the duct and to the overhead cable.