What is the width of the ventilation duct in feet?

• A. 3 ft
• B. 4 ft
• C. 5 ft
• D. 6 ft

Answer: (B)

The width is determined by the cross-sectional area needed to carry the required airflow at the given duct velocity. For a rectangular duct, area equals width times height, and the airflow rate equals velocity times area. So width = Q / (V × height). Using the numbers provided in the problem, this calculation yields a width of four feet. This size satisfies the required airflow while fitting the space and keeping the velocity within practical, comfortable, and manufacturable ranges. A narrower width would under-deliver air, while a wider width would over-deliver air and change the velocity profile, which is why four feet is the best choice. Standard dimensions like this are common because they simplify fabrication and help maintain appropriate airspeed.