Chimney Terminology

Ash Pit: A small trench located in the base of a fireplace used as a receptacle for ashes.

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Anchor: A band of steel that is secured to the bond beam. An anchor is critical in securing a chimney to the rest of the house and will provide support for both in the event of any kind of natural disaster.

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Carbon Monoxide: A byproduct of burning wood that is both odorless and colorless. Carbon monoxide is toxic to humans if inhaled in high concentrations.

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Chase: An outer barrier or cover for a manufactured

Class-A chimney that is used for aesthetic purposes to hide the chimney from plain view.

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Chimney: One or more vertical passageways that are used to emit toxic gases from a fireplace, stove, boiler or furnace.

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Chimney Cap: A cover that is installed on top of a

chimney that allows the proper ventilation of gases into the atmosphere but prevents the intrusion of water, leaves, branches, animals or other debris into the chimney.

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Chimney Fire: A fire that occurs due to the ignition of

creosote along a chimney’s inner wall. A fire hazard exists if a quarter of an inch of or more of creosote is present.

Grate: A raised metal grid where wood is placed in the firebox to prevent the fire from having direct contact with the hearth.

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Hearth: The floor of a firebox.

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Outer Hearth: The area located directly outside of a

firebox opening. The outer hearth is constructed of

masonry of other non-combustible or heat resistant

materials.

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Masonry Chimney: A chimney made of stone, brick,

cement, or other masonry materials that are field

constructed, often times at the same time the house is originally built (the most traditional type of chimney).

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Parging: A mixture of mortar that is spread over the inside of a chimney to prevent gas from escaping before exiting through the flue and to repair minor cracks in a chimney.

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Pyrolysis: A chemical decomposition of a fuel (usually wood) that is caused by heat, not combustion. Pyrolysis occurs when a piece of wood is placed in a fire but does not have enough oxygen to ignite. The by-product of this process is char.

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Smoke Chamber: Area of a chimney above the damper and smoke shelf but before the flue that compresses the gases and smoke from a fire in order to facilitate the proper escape of harmful gases out of the flue.

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Smoke Shelf: A flat area located behind the damper that is above the back wall of the firebox. The smoke shelf acts as a collecting place for anything that falls down the chimney and is important in stopping downdrafts.

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Throat: Area of a chimney that connects the flue to the firebox. The throat is usually where a damper is placed.

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Wythe: A barrier of masonry or bricks that separate one flue from another in a chimney.

Creosote: A highly combustible material that is a

by-product of burning wood or coal which builds up on the inner wall of a chimney over time. Creosote is black or dark brown in color and usually has the texture of tar or even glass.

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Crown: The sloped, concrete top of a chimney that

prevents the buildup of water around the opening. A

crown also acts as a separator between a flue liner and the inner wall of a chimney.

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Damper: A retractable plate located at the throat of a

chimney. When a chimney is not in use the damper is typically left closed in order to impede the flow of air into a chimney thereby conserving energy. When a chimney is in use, the damper is left open to ensure the hazardous gases associated with a chimney are safely emitted.

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Firebox: Area located in the opening of a chimney where wood is placed for burning.

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Flashing: Sheet metal that is placed in the area where the roof and chimney meet. Flashing is used to form a tight seal between the roof and chimney for the purpose of keeping rainwater or any other moisture from leaking under the roof.

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Flue: The passage in a chimney through which all gases are vented into the atmosphere.

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Flue liner: A metal tube that is inserted in the chimney to protect the inner chimney wall and the rest of a home from the hazardous gases associated with incomplete combustion of carbon. A flue liner is typically installed in older homes that may have gases leaking out of the chimney and into the house before being vented from the flue.

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