What is the minimum air changes per hour based on ventilation type?

• A. 0.5 air changes per hour if mechanical, 1 air change per hour if natural
• B. 1 air change per hour if mechanical, 0.5 air changes per hour if natural
• C. 2 air changes per hour regardless
• D. 0 air changes per hour

Answer: (A)

The idea is that the required air changes per hour depend on how the ventilation is provided. Mechanical ventilation delivers a controlled, continuous flow, so a smaller minimum rate can still maintain adequate indoor air quality. Natural ventilation, on the other hand, relies on openings and weather conditions and can be unpredictable, so a higher minimum rate is used to help ensure pollutants are diluted even when conditions aren’t favorable. That’s why 0.5 air changes per hour for mechanical and 1 air change per hour for natural is the best fit. The other options either swap the values, set the same rate for both types, or suggest no ventilation, which wouldn’t meet typical IAQ expectations.