An inline fan is a fan used to intake and exhaust air. In our grow room or  grow tent , we want to exchange the air at least once every 3 minutes. An inline fan can bring air in, and send old air out through the intake and exhaust systems.Inline fans are also responsible for managing temperature and humidity levels in the growing space. These fans sit inside ducting in the ventilation system, or in the case of an air cooled reflector, right inside the hood.