What occurs below the neutral pressure plane in terms of air movement?

Air movement below the neutral pressure plane typically involves outside air being drawn into the home. The neutral pressure plane is the height at which the pressure inside a building is equal to the pressure outside. Below this plane, the pressure difference generally favors the inward movement of air from the outside, driven by natural forces like wind or stack effect.

In residential settings, air tends to flow from areas of higher pressure to areas of lower pressure. Therefore, when the pressure inside is lower than the outside pressure, which often occurs below the neutral pressure plane, outside air is pushed into the home. This can have implications for indoor air quality and radon entry, as it allows contaminants, including radon, to come in alongside the fresh air from outside.

On the other hand, the other potential answers do not accurately describe the air movement mechanics applicable in this context, as they suggest scenarios that are not aligned with how pressure differentials work in buildings.