Nailor 0716-4 is ideal for installation in tight places that require a fire and heat barrier in air duct openings penetrating fire resistive membrane ceilings. Adjustable model 0716-4A for volume control available. Model 0720 ceiling radiation damper, which functions as a fire and heat barrier in air duct openings that penetrate fire resistive membrane ceilings, is for use in lieu of hinged door type dampers in any UL floor/ceiling assembly with up to a 3 hour fire resistance rating where air ducts are permitted.