Opposite to beneficial pressure devices, these devices exhaust air with the developing, making sure that any uncontrolled air getting into the developing is from outside the house to inside. b(1) : the circulation and exchange of gases while in the lungs or gills that is standard to respiration (two) : https://ventilationinstallation80012.bcbloggers.com/36548565/the-2-minute-rule-for-ventilation-ductwork