High velocity AC does the same thing with one major change: it doesn’t require those bulk metal ducts. Instead, it uses small diameter flexible tubing that can be run inside walls. A high velocity AC system also does away with those metal vents in the floor or ceiling. Instead, the rectangular vent is replaced by a round circular vent that’s less than half the size of a traditional vent.

High Velocity AC is often the ONLY answer for very old homes that do not have space for traditional duct work.