When warm air exits a home through its attic during the winter, where is makeup air most likely going to come from?

Makeup air is the air that replaces air that has exited a building, and understanding its source is crucial for maintaining indoor air quality and comfort. When warm air escapes through the attic during winter, it creates a negative pressure inside the home, which pulls in replacement air from outside.

The concept of the neutral pressure plane refers to the level in a building where the pressure inside is equal to the pressure outside. Above this plane, the pressure is typically lower, meaning that air will flow out, while below it, the pressure is higher, allowing for air to flow in. During the winter, as warm air rises and escapes above the neutral pressure plane, the makeup air will naturally be drawn from areas below that plane, such as the basement or lower levels of the home. This is because air pressure differentials push air from higher pressure areas to lower pressure areas.

As a result, makeup air most likely comes from below the neutral pressure plane, ensuring that any air entering the home to replace the exiting warm air will arise from those lower pressure regions. This mechanism emphasizes the importance of understanding air movement and pressure dynamics in building performance, particularly in cold weather scenarios.