For use when installing a Model SSII chimney in an A-frame, mobile home, or in a ceiling under a narrow section of roof. It provides a finished installation at a ceiling level and will support up to 20' of 6" or 8" diameter chimney. The part also can be used to provide shielding from insulation when installed in an unoccupied attic space. The support box assembly is comprised of a black box designed for installation inside 16" O.C. joists, a cylindrical shield, support bucket, ceiling trim, and 4 screws. B = 24". C = 14-1/4".