HVAC uses of flexible air duct have grown exponentially over the last two decades, all over North America. Contractors and installers say they like it, and some find it indispensable.

He says that ductwork designs prepared by engineers and architects will generally limit flex duct sections to 8 feet in length because of its drawbacks in longer runs. Lederer does not use flex ...

A proposal to limit the use of flexible ductwork in residential construction has some people in the industry bent out of shape.