6 Inch Ducting: Standard for most kitchens and can handle up to 600 CFM. Not sufficient for any range hoods over 600 CFM.
8 Inch Ducting: Common for mid-range to high-powered residential range hoods. Can handle up to 1000 CFM, making it suitable for larger kitchens and more powerful range hoods.
10 Inch Ducting: Suitable for range hoods that go over 1000 CFM. Typically, range hoods this strong are only required for very wide ranges (36 inches or bigger) or for BBQ's.
It is important that when installing your ducting you match the same size as the range hood and never reduce to a smaller size. Reducing to a smaller size will decrease the efficiency and significantly increase the noise.