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.