Unlined chimneys are not prohibited but the best arrangement is one in which all flues are lined with fire clay tile, joints well set in mortar, and each flue separated by a partition of brick. Only sound, uncracked tile should be put in place.
Fireplace walls must be of ample proportions to support the chimney and at least eight inches thick. It is further suggested that they be lined with fire brick.
The woodwork around fireplaces must not be closer than four inches to the back wall of a chimney and floor beams must be two inches away from a chimney wall. The space between should be filled with loose crushed cinders or other porous incombustible material to form a fire stop.
Plaster for exterior walls of a chimney should be applied direct or on metal lath. No wood furring or lath.
The hearth, which may be of brick, stone, tile, or concrete, must be supported by a masonry trimmer arch or similar fire-resisting construction. Both hearth and arch should be at least twenty inches wide and not less than two feet longer than the width of the fireplace opening.
If the mantel is of wood, it must not be placed within eight inches of the jambs, or twelve of the lintel.
The minimum height of chimneys above the roof line is two feet for hip, gable, or mansard roofs, and three for flat ones.
Chimney caps must not reduce the effective draft area of flues.
In connecting the smoke pipe of a heating plant, incinerator, or water heater to its flue in the chimney, the opening must be built with a fire clay tile collar and the smoke pipe should not protrude into the flue beyond the collar. Otherwise, the efficiency of the draft is materially impaired.
In addition, home owners may have other features installed that will do much to increase heat production of fireplaces and convenience in the use of them. One is the steel fireplace form, built into the chimney. This takes the place of jambs, back, throat, smoke shelf, and smoke chamber and is so designed that behind sides and back there is an air space opening into the room through intake and outlet vents on either side of the fireplace. The cold air of the room is drawn into this space, heated by radiation and returned. It acts on the order of a hot air furnace and can be used to advantage in new fireplaces or in old ones too much out of repair to be used without rebuilding.