Supply Air grille cutting off the air exchanging between indoors and outdoors,the grille can prevent air outdoor flow into the r Supply air grille(HVAC,Air grille ,Air diffuser,Air register,air vent,air louver)F-DB-L Saggy grille uses for expeling exhaust air from a air-conditioning room in positive pressure. Under normal circumstances, the blades sag naturally for gravity, cutting off the air ...