What is the open capacity of an Auxiliary Fan?

• A. The air flow the fan can draw when unrestricted.
• B. Air flow with restrictions.
• C. Electrical power rating.
• D. Noise level.

Answer: (A)

Open capacity is the maximum air flow the auxiliary fan can move when there are no restrictions in the path. It represents the free air delivery, measured with zero static pressure or obstructions, so the fan is essentially in unobstructed air. This is the reference point on the fan curve: the highest flow the fan can achieve before any duct losses or resistance reduce performance. In practice, once you connect ducts or face resistance, the actual flow is lower. The other options describe flow under restriction, electrical power, or noise, none of which define open capacity.