In winter, where is air most likely to enter a home from the outside?

Air is most likely to enter a home from the outside during winter below the neutral pressure plane. This is because the neutral pressure plane indicates the height at which the pressure inside and outside the building is equal. Below this plane, the building’s internal pressure is typically lower than the external pressure, particularly in winter when heating systems create conditions that pull outside air into the living space.

This phenomenon is often exacerbated by the stack effect, where warm air rises, creating a pressure difference that encourages cold outdoor air to be drawn in from lower areas of the house. Common entry points for this air include cracks in the foundation, gaps around doors, and other openings located lower in the building.

While air can also enter through other means such as leaks in windows, or from the basement, those sources alone are not as significant as the influx occurring below the neutral pressure plane, especially during winter when heating systems are running and creating negative pressure zones in homes. Furthermore, air entering through above the eaves or through the basement typically does not drive the same level of air infiltration as what occurs below the neutral pressure plane.