Under ASHRAE 62.1-2022, what determines filtration requirements for outdoor air?

• A. Filtration is always required at MERV 13 regardless of air quality.
• B. Filtration requirements apply if particulate matter exceeds national standards.
• C. Filtration is never required.
• D. Filtration requirements depend on user preference.

Answer: (B)

Outdoor air filtration requirements in ASHRAE 62.1-2022 are driven by the quality of the outdoor air. When particulate matter in the outdoor air exceeds national standards, the standard requires filtration to be applied to the incoming outdoor air to reduce pollutant levels before it enters the breathing zone. This helps protect occupants from outdoor-origin pollutants even as ventilation continues. If outdoor air quality meets or is better than the standards, there’s no mandatory outdoor-air filtration beyond what is already provided for general filtration of recirculated air.

The other possibilities aren’t correct because filtration isn’t required regardless of air quality, nor is it never required, and it isn’t dictated by user preference. It depends on objective outdoor air quality relative to established standards.