24" Square Ceiling Support Box for 8" Diameter Class-A Chimney PipeThe 24" Square Ceiling Support Box provides safe passage of double wall chimney pipe through your floor or ceiling and supports the weight of the chimney in through the ceiling installations. The Ceiling Support Box can support a maximum of 50 ft of chimney pipe and includes trim to provide a finished look inside the room. The support box and trim is painted black to match the black single wall stove pipe. Attached to the bottom of the ceiling support