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.