The definition of HVAC Make Up Air is the air that is brought into a building to replace air that has been exhausted from the building. This air is typically used to maintain the indoor air quality and to provide fresh air for the occupants. HVAC Make Up Air is usually provided by a mechanical system, such as an air handler, that brings in outside air and distributes it throughout the building. The air is then heated or cooled to the desired temperature and humidity levels. The air is then circulated throughout the building to provide a comfortable environment for the occupants. The HVAC Make Up Air system is an important part of a building’s overall HVAC system and is essential for providing a healthy and comfortable indoor environment.