HVAC exhaust is a system of ducts and fans used to remove stale air from a building. It is typically used in commercial and industrial buildings, but can also be used in residential homes. The exhaust system works by drawing air from the building, filtering it, and then expelling it outside. This helps to maintain a healthy indoor air quality by removing pollutants, odors, and other contaminants. The exhaust system also helps to regulate the temperature and humidity levels in the building.