DuraChimney 14″ Class A Chimney Pipe Firestop The DuraChimney II 14″ Class A Chimney Pipe Firestop Assembly is a component that is used in a typical venting installation. Use in ceiling/floor penetrations above fireplace. Firestop is not required when passing through the roof. Fits on underside of ceiling. Features: Type: Firestop. Collection: DuraChimney II. For DuraChimney II 14″ Class A Chimney Pipe. Used in Ceiling/Floor Penetrations Above Fireplace. Specifications: Overall Dimensions: 23.62″ (W) x 23.62″ (D). Firestop is 1″ Thick.