Anatomy of a Chimney
Of all the complex features in your house, a chimney is perhaps the simplest – but there's more in there than you may think. If he were not so magical, Santa could not possibly get through to the fireplace.
1. At the top there's the chimney cap (sometimes called a crown, wash or splay) that keeps weather and animals from getting in.
2. The "flue" refers to the open space inside the chimney where air can flow.
3.The chimney chase is the portion above the roof line.
4. The flue is lined with metal to reduce the risk of fire.
5-6. The smoke chamber and smoke shelf for the open space where smoke rises through the damper.
7. The damper is where you open and close access to the flue.
8. The mantel.
9. Fireplace face.
10. The lintel is the horizontal metal plate supporting the bricks above the firebox opening.
11. This space leading to the damper opening is called the throat.
12. The firebox is lined with firebrick designed to withstand the heat.
13. The firebox.
14. The outer hearth, usually brick.
15. The inner hearth, usually cement.
16-17. The ash dump door is a metal trap door through which you can sweep the ash through an opening to the basement level.
18. A clean-out door opens to the outdoors.
19. The ash pit must be cleaned out periodically if the ash dump door is used.
The chimney cap plays an important role in the chimney system. Often made of metal, stainless steel or copper, the chimney cap is responsible for protecting the chimney's flue from animal invaders, water damage and downdrafts. Failure to install a chimney cap is like leaving a window open on the top of your home. Raccoons and squirrels can enter an unprotected chimney for nesting. Water can damage the mortar inside the chimney and lead to mold growth and unpleasant smells. The chimney cap can also prevent sparks from landing on your roof, which could lead to a serious home fire.
Trainees at the Plainfield, Ind.-based Chimney Safety Institute of America witness a planned chimney fire. There are about a dozen CSIA-certified sweeps in central Indiana. Photo by Brandon Smith
The Risk of Chimney Fires
It's very important to have your chimney cleaned on a regular basis -- at least once every two years -- to remove soot and creosote that builds up inside. Creosote remains flammable and sparks floating up the chimney can start a fire that can quickly spread to your house.
According to the National Fire Protection Association, about eight percent of all home fires are related to fireplaces and chimneys, and most of these fires are caused by creosote build-up.
Creosote can be found in more than one form, but in the context of chimneys it is a dark brown or black tar left behind by wood smoke as it passes over a solid object like the inside of your chimney.
In small quantities it poses little risk, but because it is flammable the risk increases because sparks or even just heat can cause it to ignite.
Perhaps the most important thing to know about a creosote fire is its potential to spread very quickly throughout the home, often without any warning.
According to a study of the causes of fires conducted by the Fire Analysis and Research Division of the National Fire Protection Agency, the leading factor contributing to home heating fires was failure to clean creosote from solid-fueled heating equipment, primarily chimneys.
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Whoever you hire, you'll usually save money if you schedule your cleaning during the warmer months when chimney cleaning and inspection companies aren't as busy.