Masonry chimney flues shall be equipped with a cleanout opening that has a minimum height of 6 inches (152 mm). The upper edge of the opening shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The cleanout shall be provided with a tight-fitting, noncombustible cover.
Exceptions: Cleanouts shall not be required for chimney flues that serve masonry fireplaces if the flues are provided with access through the fireplace opening.