Q & A

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Eric Vinje

Hi Bill –

Great question. When setting up a ventilation system we typically figure a 7% loss in CFM for every 25 ft. when using flexible ducting (a 3% loss if using metal duct pipe). You should also factor a 3% loss for every 90 degree bend in your ductwork. Keep in mind that these are ballpark numbers — each system is unique and actual numbers may vary.

The following post should also help:


Good luck!