Anatomy of a Chimney
There’s far more to chimneys than meets the eye. While the average home owner is only vaguely familiar with the contents that extend beyond the hearth and the chimney, your fireplace and chimney could consist of up to 22 parts. Knowing about these parts and their functions can be useful in general maintenance, troubleshooting, or even talking with a fireplace and chimney expert about your service. Use the following guide to understand the various parts of your chimney, and be prepared for your annual chimney inspection!
1. Chimney Crown - Your chimney crown protects your chimney from water damage entering through small cracks. Without a proper chimney crown- or if you have a cracked one, rain water seeps into the bricks and mortar of your chimney structure. Even minute amounts of water can result in brick flaking, mortar deterioration, and unsightly salt deposits on your chimney. Without a good crown that has been sealed your chimney does not have any protection. Eventually, the bricks and mortar break up enough that the chimney is no longer structurally sound. You can read more about chimney crowns here.
2. Flue - A flue is simply a passage for conveying exhaust gases from an appliance to the outdoors. A flue may be a duct, pipe, vent, or chimney. An unlined chimney is technically a flue, even though an unlined chimney is a fire hazard.
3. Flue Lining – For a safe flue, a lining must be used to ensure minimal accumulation of flammable debris. This lining should be stainless steel or specially formulated lining tile. In our all about chimneys article we talk further about the importance of the flue lining and problems you may be facing with your flue lining.
4. Smoke Chamber – The purpose of the smoke chamber is to gently compress the byproducts of combustion into a smaller space (the chimney) without causing back draft. The use of sloping walls, in conjunction with good fireplace design and maintenance, helps facilitate this.
5. Chimney Damper – Chimney Dampers are lever or pulley activated doors within your chimney. They can be closed to prevent energy loss when your fireplace isn’t being used. They also help prevent rain water or animals from entering your home if your chimney cap doesn’t restrict this. Wondering how this relates to a chimney cap? This article explains.
6. Smoke Shelf - This shelf is just behind the chimney damper. Flat, it catches falling debris and rain water, and helps with the transition of large volumes of smoke into the small chimney.
Chimney Chase – This generally refers to a factory made case used around factory made chimneys. This function is taken by masonry chimneys in homes that have them.
Anatomy of a Fireplace
7. Mantle – Also known as mantel piece or mantel shelf, this piece of hardware is more than a surface to display family photos and hang stockings. It’s primary use was to help catch smoke and prevent it from entering the home, but as fireplaces have evolved its use isn’t as important as it once was.
8. Lintel - This piece is place just above the fireplace opening. Lintels are used in archway, door and window openings to help bear the load created by opening such spaces.
9. Throat - This is the space just below the damper and just above the firebox, where the fire first passes through.
10. Firebox - The firebox is the section of the chimney system in which a person builds a fire. A proper firebox is lined with firebrick, a substance of refractory ceramic, which can become cracked or weakened after years of use. This area of the chimney is often in need of repair. It is recommended to have a thorough inspection of the firebox every five years or so depending on fireplace usage.
11. Hearth Extension – This is the space that occupies the floor just outside of the firebox. It’s made of heat resistant material such as tile or brick to reduce the chance of fires.
12. Hearth – This is the space on which the fire actually burns. As with the firebrick, it must be able to handle both the potential corrosiveness of the burned material and the high heats it can be subjected to.
13. Ash Dump – Lies directly below the ash door dump, this is the space ash falls through once the ash dump door is opened.
14. Ash Pit – Below the ash dump, this serves as a collection space for dumped ash. It should be emptied frequently to prevent excess accumulation of flammable byproducts.
15. Clean Out Door – This door is used to clean out the ash dump. It frequently is located outside or in the basement to make ash removal easy.
16. Footing – This is the horizontal surface under the ash pit. Generally made of concrete, the chimney should be securely placed in relationship to the footing to prevent problems later on.
17. Foundation – The lowest part of the chimney walls, this is made of heavy duty brick or cinder block. It’s used as structural support for the rest of the chimney, and is exposed to potentially hot ash. As such, it should be sturdy.
Fireplace Face – This is the area between the mantel and the fireplace itself. Traditionally brick, it must be sturdy enough to handle the heat of the fireplace below it.
Ash Dump Door – This door allows you to easily remove ash from your firebox. Placed in the middle of your firebox, it can opened to dump the ash into the ash dump.