When sizing an exhaust fan, what describes the relationship between CFM, duct size, and static pressure?

• A. The CFM should be fixed regardless of duct size.
• B. Static pressure has no effect on CFM.
• C. The fan must deliver the required CFM against the static pressure given the duct size; larger ducts reduce velocity and pressure, while smaller ducts increase them.
• D. Smaller ducts reduce both velocity and pressure.

Answer: (C)