Under what condition does infiltration typically occur?

Infiltration typically occurs when the air pressure inside a building is lower than the air pressure outside. This pressure difference causes outside air to be drawn into the building through various cracks, openings, and porous areas in the building envelope. Lower indoor pressure can arise due to mechanical ventilation systems, exhaust fans, or simply the stack effect, where warmer air rises and creates a vacuum at lower levels.

The movement of air into the building represents a loss of conditioned air, which can impact energy efficiency and indoor air quality. Understanding this dynamic is crucial for building analysts as they evaluate energy use and implement strategies to manage air infiltration effectively. Addressing issues with infiltration can lead to improved energy efficiency by reducing unwanted heat loss or gain through the building envelope.