S.C. Code § 5-25-740
All heater pipes from hot-air furnaces, where passing through combustible partitions or floors, must be doubled in tin pipes with at least one inch air space between them. Horizontal hot-air pipes leading from the furnace shall not be less than six inches from any woodwork, unless the woodwork be covered with loose fitting tin or the pipe be covered with at least half an inch of corrugated asbestos, in which latter cases the distance from the woodwork may be reduced to not less than three inches. No hot-air pipe shall be placed in a wooden stud partition or any wooden enclosure unless it be at least eight feet horizontal distance from the furnace. Hot-air pipes contained in combustible partitions shall be placed inside another pipe arranged to maintain half an inch of air space between the two on all sides or be securely covered with half an inch of corrugated asbestos. Neither the outer pipe nor the covering shall be within one inch of wooden studding, and no wooden lath shall be used to cover the portion of the partition in which the hot-air pipe is located. Hot-air pipes in closets shall be double, with a space of at least one inch between them on all sides.
S.C. Code § 5-25-740