What is the term for air moving from the interior of a building to the outdoors?

What is the term for air moving from the interior of a building to the outdoors?

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

Answer: (C)

Air moving from the interior of a building to the outdoors is exfiltration. This term describes the outward leakage of indoor air through cracks, joints, and openings in the building envelope, driven by pressure differences such as wind or temperature differences. It’s the opposite of infiltration, which is air coming in from outside, and it’s different from ventilation, which is deliberate, controlled exchange of indoor air to maintain quality. Diffusion refers to slow, natural mixing due to concentration gradients and isn’t the primary mechanism for whole-building air movement. Exfiltration matters because it represents unintentional air loss that can carry heat, moisture, and pollutants out of the building.

Air moving from the interior of a building to the outdoors is exfiltration. This term describes the outward leakage of indoor air through cracks, joints, and openings in the building envelope, driven by pressure differences such as wind or temperature differences. It’s the opposite of infiltration, which is air coming in from outside, and it’s different from ventilation, which is deliberate, controlled exchange of indoor air to maintain quality. Diffusion refers to slow, natural mixing due to concentration gradients and isn’t the primary mechanism for whole-building air movement. Exfiltration matters because it represents unintentional air loss that can carry heat, moisture, and pollutants out of the building.