If soot accumulates fast or trouble is experienced with unusual smoke when firing, it is probable that the heating equipment is not being operated properly. The manufacturer or installer usually is able to suggest proper adjustments.
Investigations by the United States Bureau of Mines[5] have shown that various materials on being burned or volatilized form a vapor or smoke which settles upon soot; causing it to ignite at a lower temperature and burn more easily. For soot to burn, the gases in contact with it must have a temperature high enough to ignite it and sufficient air to support the combustion. The effectiveness of burning varies with the composition of the remover, but it also depends upon conditions being favorable. It will usually reduce somewhat the soot in a furnace and smoke pipe but not in a chimney. It has no effect on the ash mixed with the soot. This ash not only does not burn, but prevents complete burning of the soot mixed with it.
[5] Nichols, P., and Staples, C. W. REMOVAL OR SOOT FROM FURNACES AND FLUES BY THE USE OF SALTS OR COMPOUNDS. U. S. Bur. Mines Bul. 360, 76 pp., illus. 1932.
Soot removers cause soot to burn and are fire hazards. The correct and most thorough method of cleaning a chimney is to do so manually or to employ modern exhaust or vacuum methods used by furnace repairmen. However, it is inconvenient to remove soot and ash accumulations thoroughly more than once a year; hence a remover may help to keep the passages of stoves and heaters clear between annual cleanings, if deposits of soot accumulate quickly and reduce the draft.
Likelihood of success in cleaning is greater when the deposits of soot are thick, provided they do not cut down the draft too much. If burning is employed, there is less risk when it is done frequently enough to prevent large accumulations, which cause intense fires. Also, freeing the heater and pipe of soot permits better fuel burning and higher temperatures in the chimney flue, thus reducing the amount of soot likely to be deposited on the flue walls.
Common salt (rock or ice-cream salt) is not the most effective remover, yet it is the most widely used because of its cheapness, ease of handling, and general availability. Use two or three teacupfuls per application. Metallic zinc in the form of dust or small granules is often used; however, a mixture of salt and 10 percent zinc dust is more effective than either salt or zinc alone.
One of the most effective mixtures of materials readily available is 1 part dry red lead and 5 parts common salt, measured by weight. Shake these together in a can with a tight-fitting lid. As lead is poisonous, wash the hands after using. One or two teacupfuls are used per application.
Old dry-cell batteries contain suitable ingredients and when they are thrown in a hot furnace the soot usually burns. Quicker action can be had if they are chopped up.
Before a remover is used, the fire must be put in good condition with a substantial body of hot fuel on top. Close the ash-pit door and the slots in the firing door and scatter the remover on the hot coals. Close the firing doors and at once reduce the draft by partially closing the pipe dampers. The draft should not be closed so tight as to cause fumes to escape into the cellar. Let the remover "stew" for 10 to 20 minutes or until fumes stop rising from the coals; then make the fire burn fiercely by opening the ash-pit door and the damper. Shaking ashes out will help. The slots in the firing door can be opened or the door itself set ajar. If soot in the furnace will not ignite, throw a little wood or paper on the fire.