A soot pocket[2] is desirable for each flue. Deep pockets permit the accumulation of soot, which may take fire; therefore start them from a point preferably not more than 8 inches below the center line of the smoke pipe intake and fill the lower part of the chimney with solid masonry instead of extending the pocket to the base of the chimney as is often done. Clean-out doors are necessary at the bottom of deep pockets and, if used, must fit snugly and be kept tightly closed so that air cannot get in. Clean-outs should serve only one flue, for if two or more flues are connected with the same clean-out, air drawn from one to another affects the draft in all of them. Sometimes a door is placed just below the smoke pipe, but one is not really necessary since the pipe, if taken down each year for cleaning, allows removal of soot from shallow pockets through the pipe hole. [2] See soot pockets and clean-out doors in figures 12 and 35, pp. 13 and 38, respectively. 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. [Illustration: 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.