What is the primary reason exfiltration occurs?

Exfiltration, which refers to the uncontrolled escape of air from a building, primarily occurs when the air pressure inside the building is higher than the air pressure outside. This pressure difference drives air movement from the higher pressure area (inside) to the lower pressure area (outside), leading to a loss of conditioned air.

In buildings, various factors can contribute to this situation, including mechanical ventilation systems, thermal buoyancy from heating or cooling, and wind effects. When the internal air pressure exceeds the external pressure, the natural tendency for air is to flow outwards, facilitating exfiltration. This process can negatively impact energy efficiency and indoor air quality, as it might lead to heating or cooling losses and can also affect moisture levels within the building.