In fitting the smoke pipe no opening should be left around it, and the pipe should not project into the flue lining. (See [fig. 8].) The joint should be made air-tight by a closely fitting collar and boiler putty or fireproof cement. The proper construction is shown in [figure 8-B], but if the pipe extends into the flue a shelf is formed on which soot will accumulate, the flue area will be reduced and a poor draft may result.
Smoke pipes should enter the chimney horizontally, and the connection through the chimney wall to the flue should be made with fire clay or metal thimbles securely and tightly set in the masonry. If the walls are furred, no wood should be within 12 inches of thimbles or any part of the smoke pipe. The space between the thimble and wood furring should be covered with metal lath and plaster.
Fig. 9.—Smoke pipe passing through a partition. A, 7/8-inch sides of partition; B, 2 by 4 studs in partition; C, ventilating holes in the double galvanized iron ventilating thimble D. Thimble should be at least 12 inches larger than pipe S.
Flue holes when not in use should be closed with tight fitting metal covers. If the room is papered the metal covers may also be papered, provided there is no other smoke connection with the flue, or provided a protective coating of asbestos paper is first applied over the metal. If there is another connection the metal may become hot enough to scorch the unprotected wall paper or set it afire. No smoke pipe should be permitted within 18 inches of any woodwork unless at least that half of the pipe nearest the woodwork is protected properly by 1 inch or more of fireproof covering. A metal casing 2 inches from the upper half of the pipe is sometimes employed to protect woodwork directly above it. When a smoke pipe is so protected it should never be less than 9 inches from any woodwork or combustible material. The storage of wooden boxes, barrels, or any combustible should not be permitted under or near a furnace smoke Pipe.
If a smoke pipe must be carried through a wood partition the woodwork should be properly protected. This can be done by cutting an opening in the partition and inserting a galvanized iron double-walled ventilating thimble at least 12 inches larger than the smoke pipe (see [fig. 9]), or protection may be afforded by at least 4 inches of brickwork or other incombustible material. Smoke pipes should not pass through floors, closets, or concealed spaces. They should not enter a chimney in a garret. They should be cleaned at least once a year.