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Shelton, Jay W. Jay Shelton's Solid Fuels Encyclopedia. Garden Way Publishing. Charlotte, Vermont. pp. 56-83.

Abstract: This article explains the functions of a chimney and the safety precautions that must be taken when using and maintaining chimneys. A chimney carries smoke out of the house while allowing air to flow into the house to feed the fire. Hot air naturally rises and as the hot gases escape the chimney, the pressure inside the chimney becomes less than the air pressure outside the chimney. Air will be drawn into the chimney where there are openings or cracks. This airflow is known as a draft.

The article provides a detailed description of how to measure draft and what the safe measurements should be. Chimney flow capacity is also explained and formulas are provided to determine a chimney's flow capacity.

Temperature is also a factor in chimney function. In the past, it has been thought that a hotter chimney will draw more air. Once the flue-gas temperature of a chimney reaches 600 degrees Fahrenheit, its capacity rate actually begins to decrease. It is suggested that the flue-gas temperature should be around 300 degrees Fahrenheit.

The size of the chimney also affects its function. Increased height improves the flow capacity, but the capacity is not increased proportionally to the added height. The higher the chimney becomes, the more the flue gases will cool before exiting the chimney, decreasing the flow capacity. The diameter of a chimney affects the flow capacity more drastically than the height does. The diameter of the chimney should be the same size as the flue collar of the appliance it is connected to.

Chimneys are often held responsible for fires, although the exact cause is difficult to determine. Insufficient space between a chimney and surrounding combustible materials is a common cause. Improper installation and improper maintenance of chimneys are also causes. A chimney should be able to withstand chimney fires, which occur when accumulated creosote burns. They should also be equipped with easy access to inspect and the clean creosote.

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