Duct Design Principles Figure 6. Streamline the system as much as possible to minimize turbulence and resistance. Smooth, rigid ducting provides less resistance than flexable, rough ducting. Short runs of ducts provide less resistance than long runs.
Straight runs offer less resistance than runs with elbows and bends.
Duct branches should enter at gradual angles rather than right angles. Duct branches should not enter the main duct at the same point. Elbows with gradual bends provide less resistance than sharp bends. Large diameter ducts provide less resistance than small diameter ducts. Round ducts provide less resistance than square ducts.