pipe hole.

Close pipe holes, when temporarily not in use, with tight-fitting metal flue stops; but, if a pipe hole is to be abandoned, fill it with bricks laid in good mortar. This stopping can be readily removed. The practice of closing a pipe hole with papered tin is dangerous, for if there is another stove connected with the flue, the metal may become hot enough to scorch the unprotected wallpaper or even set it afire.

Proper care in setting and looking after pipe at its connection with the chimney will greatly lessen the number of fires chargeable to defective construction. Fit the pipe so that no opening will be left around it, and keep it from projecting into the flue. The connection can be made airtight with a closely fitting collar and boiler putty, good cement mortar, or stiff clay.

Smoke pipes should enter the chimney horizontally, and the hole through the chimney wall to the flue should be lined with fire-clay, or metal thimbles should be securely and tightly built in the masonry. Thimbles or flue rings can be had of 6-, 7-, 8-, 10-, and 12-inch diameters and 6-, 9-, and 12-inch lengths. If the walls are furred (fig. 12), the space between the thimbles and the wood furring should be covered with metal lath and plaster.

Figure 12.—A, Connection to chimney where furring is used. The brick are built out around the thimble as a protection against its cracking. This is a fire hazard that is frequently overlooked. B, Connection when plaster is applied directly to the masonry. Note that the pipe extends too far into the flue. It should be as shown in A.

When a smoke pipe is less than 18 inches from woodwork, the woodwork requires protection against charring. A metal casing or asbestos board 2 inches from the upper half of the pipe is sometimes employed to protect woodwork directly above it. A pipe, even so protected, should never be closer than 9 inches to any woodwork or other combustible material. Commercial fireproof pipe coverings can be purchased.

If a pipe must be carried through a wood partition, protection for the woodwork can be provided by cutting an opening in the partition and inserting a galvanized-iron double-wall ventilating shield at least 12 inches larger than the pipe (fig. 13) or by using at least 4 inches of brickwork or other incombustible material. Smoke pipes should never pass through floors, closets, or concealed spaces or enter a chimney in a garret.

Gases formed by burning the sulfur contained in coal are the main cause of corrosion of metal smoke pipes. Little corrosion occurs during the heating season, when the pipe is kept hot and dry.

The life of metal pipes can be prolonged if each summer when they are not in use they are taken down, cleaned, wrapped in paper, and stored in a dry place. This is especially true of pipe to heaters in damp cellars.

Figure 13.—A, Elevation of protection around a stovepipe passing through a frame partition; B, sectional view.

Figure 14.—Method of insulating wood floor joists and baseboard at a chimney with 4-inch walls. A single header is used as it is less than 4 feet long.

Insulation

No wood should be in contact with a chimney. Leave a space of 2 inches between the outside face of a chimney and all wooden beams or joists except when 8 inches of masonry is used outside flue lining, in which case the framing may be within one-half inch of the chimney masonry. The space between the floor framing and the chimney may be filled with porous, nonmetallic, incombustible material, such as loose cinders. Brickwork, mortar, and concrete are not suitable. Place the filling before the floor is laid, as it not only forms a fire stop but prevents accumulation of shavings or other combustible material. Subflooring may be laid within one-half inch of the masonry. Baseboards, when fastened to plaster that is directly in contact with the wall of a chimney, can be protected by a layer of fireproof material, such as asbestos, at least one-eighth of an inch thick between the woodwork and the plaster (fig. 14).

Wooden studding, furring, or lathing should not be placed against a chimney but set back, as indicated in figure 9; or the plaster may be applied directly to the masonry or to metal lath laid over the masonry. The former is the better method, as settlement will not crack the plaster. It is recommended that a coat of cement plaster be applied directly upon the outside surfaces of masonry chimneys that are to be incased by a wooden partition or other combustible construction. Metal lath, lapped 6 inches on the masonry, at the intersection of chimneys with partitions prevents corner cracks. (See plan in fig. 34.)

Chimney and Roof Connection

Where the chimney passes through the roof, provide a 2-inch clearance between the wood framing and masonry for fire protection and for expansion due to temperature changes, settlement, or slight movement of the chimney during heavy winds.