The fact remains that chimneys are being built today that will not operate because these basic needs are ignored. The annoyance and expense connected with a poorly constructed chimney will eventually have to be borne by the homeowner.
The best location for the chimney is in the center of the house, to minimize heat loss through the walls of the chimney. A chimney placed on the outside of the house will lose considerable heat. A well-constructed outside chimney will have to be several inches thicker than an inside one to compensate for this loss.
A chimney should run straight up with no angles or bends. Angles will cause resistance to the passage of air and gas through the chimney and thus cut down the draft. They also afford an excellent stop for the accumulation of heavy deposits of soot.
The interior of the chimney should be lined with fire-clay flue lining. This provides not only a smoother surface than can be obtained with either bricks or stones but also a measure of safety. The heat and oils in smoke will eventually cause ordinary mortar to disintegrate, with resulting leakage in the chimney.
There should be a separate flue for each piece of heating equipment. When two or more heating devices are connected to the same flue, they nullify each other's draft. This is Often the reason why coal-burning hot water heaters do not operate as they should. They are connected to the same flue as the main heating system and thus have little or no draft.
The top of the chimney should rise at least three feet above the top of the roof. Branches of trees should not be allowed to extend over the chimney top. Covering the top of the chimney will impair the draft, although it is quite common to see chimneys with caps of one kind or another.
No beams or girders employed in the construction of the house should protrude inside the flue of the chimney. This will have a serious effect on the draft, and is a fire hazard as well.
Stove pipes from other heating equipment should not protrude into the chimney. The end of the stove pipe should be flush with the inside of the flue.
See that all connections with the chimney, such as stove pipes, are airtight, so that the draft will not be impaired. If there is a clean-out door at the base of the chimney, keep it tightly shut and check from time to time to see that it fits tightly.
A chimney should be inspected and cleaned at regular intervals. This is especially important if very sooty fuels are burned or if the chimney suddenly fails to function properly. You can make a visual inspection of the chimney with a flashlight from the top or with a flashlight and a mirror at the clean-out door in the base.
Be on the lookout for cracks or breaks in the flue lining, loose pieces of flue tile, or large deposits of soot. Check all the masonry around the openings in the chimney where stove pipes enter.
To test the chimney for any possible leaks, start a fire in the stove, furnace, or fireplace, and when it is burning well throw on some material that will cause smoke. When the smoke begins pouring from the top of the chimney, cover it with a piece of heavy, wet cloth. This will force the smoke to find some other exit from the chimney, if one exists. In this way, any leaks in the chimney can be easily and quickly located and their location marked with a piece of chalk.
Once the leaks have been located, their size and number will govern what should be done about them. If there are a few small ones, they can be refilled with cement mortar made of 1 part cement to 3 parts fine sand. If, on the other hand, the chimney appears to be in generally poor condition, a chimney expert should be called in to examine the structure carefully and determine whether it can be repaired safely or must be completely rebuilt.
A chimney that leaks is a fire hazard, for a small piece of burning soot could pass through the opening and set fire to the roof or some other inflammable building material.
A straight chimney with a clean-out door at the bottom is relatively easy to clean. To do this, weight a burlap bag with old rags, sawdust, or some other waste material, and lower it into the chimney from the top.
Raise and lower the bag several times, and the soot will fall to the bottom of the chimney where it can be removed with a shovel and hoe. If the chimney serves a fireplace, cover the fireplace opening with a piece of cloth, hung from the mantle, to prevent soot and ashes from entering the room.
Very often, the flue area is too large for
a particular piece of heating equipment, or the draft fluctuates widely
with the prevailing wind.
This regulator is a type of damper which is opened and closed by the suction in the chimney. The regulator is first set to provide the required amount of draft. When the draft starts to increase, the disk of the damper closes far enough to reduce the draft. When the chimney draft decreases, the disk opens wider to compensate for this reduction.
In combustion, gas produces a considerable amount of water vapor. As this moisture is in a gaseous state it will flow out of the flue or chimney opening, provided it does not become chilled and thus condense into a liquid. If the chimney is well constructed and holds the heat, the vapor should have no difficulty in escaping, but if the chimney is poorly built or a large section of it is exposed to the wind and weather, the vapor will condense into a liquid.
This liquid contains certain acids which are capable, in time, of soaking through mortar joints and eventually working out of the chimney to damage wall and ceiling decorations. Homes heated with gas where such a condition exists should consult a chimney expert or the local gas company.
There are several methods used to eliminate this trouble, but it takes firsthand knowledge to know which one to select. Be sure you get someone who really understands this field, as many homeowners have paid out large sums to have their chimney rebuilt only to find that the condition still exists.
Gas-fired hot water heaters are often connected into the house chimney with several lengths of metal flue pipe. In some cases this pipe runs right up through an opening in the roof, and provides the necessary escape for the fumes from the burning gas. As a general rule, a long run of metal pipe will not hold the heat very well and in this event there will be condensation of vapors inside the pipe. This moisture may drip back down the pipe and find an exit at the pipe joints.
One simple remedy is to cover the pipe with special paper so that it will hold the heat longer. There is a special type of flue pipe made of materials that are poor heat conductors and this can be used instead of the metal pipe.