6" DuraVent DuraPlus Firestop Radiation Shield 6DP-FRS This firestop radiation shield is used in ceiling/floor penetrations when a ceiling support is not used. Not required when passing through the roof. Fits on underside of ceiling and adjusts to cover framing. Use when air-cooled chimney is required Free-floating inner 430-alloy liner maintains structural integrity in chimney fires 2" clearance to combustibles Outer diameter is 4" larger than inner diameter Triple-wall chimney For uses with wood stoves fireplaces furnaces boilers stoves ranges water heaters or other appliances fueled by wood oil coal or gas Clean smooth exterior finish .016” 430 stainless steel outer wall or .018” galvanized steel outer wall. .018” aluminized steel intermediate liner. .016” 430 stainless steel inner liner. Insulated layers plus ventilated air space. Locks tightly with a precision twist-lock connection.