what exactly does the bolded text mean? this is from the c450 manual Masonry Fireplace Requirements • The entire fireplace and chimney must be cleaned and inspected before installation. The system must meet local building code requirements. • The structure and components must be free of any defects such as cracks or broken bricks or flue tiles. Any damage must be repaired before installation. Any opening that may exist between the masonry of the fireplace and the facing masonry must be permanently sealed.