What causes negative pressure in a building?

Negative pressure in a building primarily occurs when there is an imbalance between the air being exhausted and the air being brought into the building. A lack of makeup air or combustion air is a key factor in this scenario. When exhaust systems, such as kitchen hoods, bathroom fans, or mechanical ventilation systems, remove air from the building, this creates a vacuum that must be filled by air coming from outside. If there isn’t sufficient makeup air available to replace the exhausted air, the result is a negative pressure environment.

This negative pressure can lead to several issues, such as drawing in unconditioned outside air, affecting indoor air quality, or causing backdrafting of combustion appliances, which can be hazardous. It’s important for buildings, especially those that rely on combustion processes, to have the right amount of makeup air to maintain a balanced pressure system and ensure safety and efficiency in operation.