Which term best describes the unintentional entry of outdoor air into a building?

Which term best describes the unintentional entry of outdoor air into a building?

• A. Exfiltration
• B. Ventilation
• C. Diffusion
• D. Infiltration

Answer: (D)

Infiltration is the unintentional entry of outdoor air into a building. It happens when air leaks through cracks, gaps, and other openings in the building envelope due to pressure differences between inside and outside, as well as wind and stack effects. This is not planned as part of the building’s air exchange, and it can impact energy use and indoor air quality. By contrast, ventilation is the deliberate process of bringing outdoor air in to control IAQ, exfiltration is air leaving the building, and diffusion is the slow molecular mixing through materials. So, the best term for unintentional outdoor-air entry is infiltration.

Infiltration is the unintentional entry of outdoor air into a building. It happens when air leaks through cracks, gaps, and other openings in the building envelope due to pressure differences between inside and outside, as well as wind and stack effects. This is not planned as part of the building’s air exchange, and it can impact energy use and indoor air quality. By contrast, ventilation is the deliberate process of bringing outdoor air in to control IAQ, exfiltration is air leaving the building, and diffusion is the slow molecular mixing through materials. So, the best term for unintentional outdoor-air entry is infiltration.