On the other hand, if the bottom draft and furnace doors are not air tight, though you have them closed and have the dampers open, and only a moderate breeze is blowing, the fire will burn briskly. If you want the fire to die, close the damper and the bottom draft door. When you close the damper and the bottom draft door you shut off the supply completely, or the life of fire, then it dies. Chimneys should be built to tower above the roofs of adjoining buildings, so that the air currents can pass over them unobstructed.
We have shown above that it is necessary to supply fire with air to create combustion, so we will now show what is understood by combustion.
Combustion is defined: “To burn, or burning. The process by which bodies combine with oxygen and are thus seemingly destroyed. Oxygen exists uncombined in the atmosphere to the extent of 22 per cent. by volume and more than 23 per cent. by weight.” The fact that air (and plenty of it) is absolutely necessary to produce combustion, seems foreign to most people who fire ovens, etc. These people poke a fire and give it draft as a matter of fact, but do not know why. All highly flammable material, such as pitch tar, resin, pine wood, paper, coal oil, gasolene, etc., and even gas will not burn unless mixed with a certain per cent. of air or oxygen, and all so-called inflammable (fire proof) material, such as mineral wood, prepared felt, asbestos, iron, steel, etc., can be entirely consumed by fire if subject to sufficient blast. Under ordinary conditions, so-called fire-proof material will not burn, but throw them into a blast furnace—one equipped with a powerful blower—and watch the results. In a short space of time you will find nothing left to indicate that such material had been thrown into the furnace.
The above illustration is given simply to show what a necessary factor air is to produce combustion even in a limited degree. Not only is air necessary to produce combustion, but the more air or draft you give a fire the more perfect the combustion, and the more perfect the combustion, the greater the heat it produces, and the greater the heat produced, the less fuel is required. Air is less expensive than either wood or coal; bear this in mind and profit by it. You have learned the necessity of using the poker frequently, and you have learned what is meant by draft and combustion. Now be guided by what you have learned.