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

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)