Which option shows the correct maximum ducting for a single fan?

Which option shows the correct maximum ducting for a single fan?

• A. 50 ft
• B. 100 ft
• C. 25 ft
• D. 75 ft

Answer: (A)

Air flow is reduced as duct length increases because every foot of duct and each bend adds friction loss. A single fan is sized to deliver the required ventilation up to a certain length; beyond that limit, the fan can’t maintain enough pressure or volume to properly ventilate spaces or control smoke. So the correct choice is the shorter duct run that stays within what one fan can effectively handle. The other lengths would exceed what a single fan can reliably push through, leading to insufficient ventilation. If longer ducting is needed, add another fan or reconfigure the system to share the load rather than extending a single run past its capability.

Air flow is reduced as duct length increases because every foot of duct and each bend adds friction loss. A single fan is sized to deliver the required ventilation up to a certain length; beyond that limit, the fan can’t maintain enough pressure or volume to properly ventilate spaces or control smoke. So the correct choice is the shorter duct run that stays within what one fan can effectively handle. The other lengths would exceed what a single fan can reliably push through, leading to insufficient ventilation. If longer ducting is needed, add another fan or reconfigure the system to share the load rather than extending a single run past its capability.