What is the definition of a rapid make up air? Rapid make up air is a system that uses fans to quickly replace air that has been lost due to any form of ventilation, such as exhaust fans. This ventilation of air is necessary to maintain a healthy indoor environment, as it helps to reduce pollutants and levels of humidity. Rapid make up air systems are commonly found in commercial buildings, such as restaurants and factories. These systems are often used in conjunction with other air conditioning equipment, such as air-handling units, to ensure optimal air quality. The system works by using fans to draw in fresh air from outside, or from other areas within the building, and then redirecting it into the building via vents. This new air replaces the air that has been lost, which helps to ensure that the building stays at a comfortable temperature and humidity level. The fans used for rapid make up air systems can be powered by electricity, or by natural gas, depending on the needs of the building. Rapid make