What is the minimum outdoor ventilation air for a 1000 sq ft theater lobby?

• A. 1800 cfm
• B. 2400 cfm
• C. 3600 cfm
• D. 3000 cfm

Answer: (D)

Outdoor ventilation in spaces like a theater lobby is driven by how the space is used and how many people it must serve. For assembly areas such as theaters, a practical design rule is around 3 cubic feet per minute of outdoor air for each square foot of floor area. This ensures enough fresh air to dilute contaminants during peak occupancy. So for a 1000 ft² lobby, 3 cfm/ft² × 1000 ft² equals 3000 cfm. That rate provides a reasonable minimum to maintain indoor air quality under typical crowding. If occupancy were higher or if a code required additional per-person ventilation, you would use the higher value, but 3000 cfm serves as the common minimum for this size.