Openings Into the Chimney
No range, stove, fireplace, or ventilating register should be connected with the flue being used for the heating apparatus because this is a frequent cause of unsatisfactory operation. Fires may occur from sparks passing into one flue opening and out through another where there are two connections to the same flue. If an abandoned fireplace chimney is to be used for a range or stove, close the fireplace flue tight about a foot below the smoke pipe hole.
Figure 11.—Greater resistance to the weather is provided by building the exposed upper section of a chimney with 8-inch walls. Also the mortar joint, in which the counter-flashing is embedded, is not so likely to fail as it is when the wall is only 4 inches thick.
Gas-fired house heaters and built-in unit heaters, if not connected to a masonry chimney, may be connected to flues of corrosion-resistant sheet metal not lighter than 20-gage, properly insulated with asbestos or other fireproofing material that will comply with the recommendations of the Underwriter's Laboratories, Inc. Such flues should extend through the roof.
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.