Low air leakage, optimal airflow characteristics and less pressure drop allow smaller and more efficient air moving equipment. Round shape is stronger, allowing the use of lighter gauge, less costly metals. Efficiently manufactured from strip steel to any diameter.
Numbers make sense!
In following charts you may see that a 40″x20″ duct is equivalent to 30″ spiral pipe
4ft rect duct 40″x20″ weights: 57.4 lb (with 22 Ga)
4 ft spiral pipe 30″ diam weights: 40.84 lb (with 24 Ga)
