Common chimney and fireplace terms, defined.




Aluminum Liner - Aluminum can be used as a relining pipe, when relining flues for low-efficiency gas furnaces or water heaters. These devices produce neither enough heat nor enough moisture to constitute the need for a more durable stainless steel relining pipe.

Andiron - Andiron or firedog, is a bracket support, normally found in pairs, on which logs are laid for burning in an open fireplace, so that air may circulate under the firewood, allowing better burning and less smoke. Much like a fireplace grate.

Ash - The white/grey powdery residue left when combustible materials such as wood and other biomass is burned.

Ash Dump - An opening located at the bottom of the fireplace, through which ashes can be dumped. Often, there is a door covering the opening.

Ash Pit - A storage compartment for ashes, located underneath the ash dump. It is usually quite large and should have a access door for cleaning out the ashes periodically.


Baffle - An object or plate installed in an stove or fireplace to change the direction of flue gases often to help burn more effectively. 

Biomass - Biomass is organic material that comes from plants and animals, and it is a renewable source of energy. When biomass is burned, the chemical energy in biomass is released as heat. Examples of biomass include:

  • Wood and wood processing wastes. Often in the form of pellets for pellet stoves.
  • Agricultural crops and waste materials such as whole, husked corn kernels used in corn stoves.

Blower - A fan with a motor that is often installed in a fireplace or stove to help distribute the heat being produced.


Carbon Monoxide - An odorless, colorless, tasteless poisonous gas that is a byproduct of incomplete combustion. Carbon monoxide can be fatal if not detected. Please see our Carbon Monoxide Page for more information.

Certified Chimney Sweep (CCS) - An individual The nationally recognized credential provided by the Chimney Safety Institute of America (CSIA) is the measure of a chimney sweep’s knowledge about the evaluation and maintenance of chimney and venting systems. A CCS credential holder is trained in the sweeping and inspection of different chimney systems, operation of the necessary equipment, health and safety considerations, codes, clearances, standards and practices of the chimney service trade.

Chase Cover - A metal cover that fits over your chimney chase (generally on chimneys with wood, metal, or vinyl siding) to prevent water from entering the chimney.

Chimney Chase - The area or structure around metal flue pipes. The chase is usually built with wood or steel studs with an exterior that can include brick/stone veneer or wood siding or stucco

Chimney - One or more passageways, vertical or nearly so for conveying flue gases from the appliance to the outside atmosphere.

Chimney (or Flue) Cap - A protective covering or housing for the top of a chimney. Often, chimney caps have a lid to protect from rain, snow and sleet and a screen mesh of some sort to keep animals out.

Chimney Cleaning (Sweeping) - The process of removing soot, creosote, and debris from a chimney. Soot and creosote are by-products of combustion and should be removed regularly from the chimney to help prevent a chimney fire. Chimney cleaning along with an inspection should be preformed as part of an maintence schedule to ensure your chimney operates as efficiently and safely as possible.

Chimney Connector - The pipe connecting a fuel-burning appliance to a chimney. Most commonly made from galanized steel, stove black pipe, or a listed double-wall pipe system.

Chimney Liner - The inner portion of the chimney that contains the products of combustion. It can be made of clay tiles or of metal. The flue chimney liner is one of the most important part of the chimney system. It must be able to contain the products of the combustion process. This means that any holes, cracks or deteriorations must be repaired or replaced to ensure the preformance and safety of the chimney system.

Corbel - Units of masonry projecting from or projecting upward and outward from the face of a wall or chimney in courses to form a support or ledge for a beam, rafter, or other member.

Cord (of wood) - The cord is a unit of measure of dry volume used to measure firewood and pulpwood in the United States and Canada. A standard cord is a neat stack of wood that has a volume of 128 cubic  feet. It measures 4 feet high, 4 feet wide and 8 feet long. This includes the air between the wood. The actual wood volume is usually around 90 cubic feet. See our article "What is a Cord of Wood?" for more information.

Corn Stove - A corn stove is designed for whole, shelled corn kernel combustion and is similar to a pellet stove. The chief difference between a pellet stove and a dedicated corn stove is the addition of a metal stirring rod within the burn pot, or an active ash removal system. These vary in design slightly, but usually consist of one long metal stalk with smaller rods welded at a perpendicular angle, in order to churn the burn pot as it spins. An active ash removal system consists of augers at the bottom of the burn pot that evacuate the ash and clinkers. During a normal burn cycle, the sugar content within corn (and other similar bio-fuels) will cause the ashes to stick together, forming a hard mass. The metal stirring rod breaks apart these masses, causing a much more consistent burn. 

Creosote - A type of carbon rich chemical released during the burning of wood and other fossil fuels when there is a lack of adequate airflow. As the smoke rises through the chimney it cools, causing water, carbon, and volatiles to condense on the interior surfaces of the flue. This appears on the flue as a hard, dark, and shiny coating.

Cricket - (also referred to as a Saddle) A ridge that extends from the back of the chimney to the slope of the roof, with the purpose of shedding water away from the connection between the chimney and the roof.

Crown - A chimney crown is the top surface of a chimney formed with concrete or mortar and poured on top of the chimney and extends out passed the stone or brick and typically has a drip edge built in to the underside to prevent water from entering the masonry below. Crowns generally have a slope away from the center of the flue stacks.

Crown Wash - The crown wash is much more popular because it is much more cost effective and is usually just cement sloped down from around the flue tiles feathered to the edge of the stone or brick.  Both share the common goal of keeping weather out from the very top of the chimney.

CSIA - The Chimney Safety Institute of America or CSIA is a non-profit, tax-exempt educational institution dedicated to chimney and venting system safety. Hiring a CSIA certified chimney sweep means your sweep has been trained and is up to date on industry standards and best practices. At minimum you r sweep should be supervised by a CSIA certified sweep.


Damper - A damper is a device for controlling the flow of air or smoke in a chimney or woodstove. In its most common form, it is a plate located in the fireplace or stove pipe with a control handle. For some stoves there is an additional air control damper located on the exterior of the stove.

Damper Cap & Top Mount Damper - Located on the top of the chimney. Works by closing off the top of the flue when not in use so that cold air does not enter the home and that heat/cold air does not get drawn up an open flue. A cable is run down the side of the flue and attached to the side firebox wall. The cable controls the opening and closing of the damper. Damper caps are like any other chimney cap but with an integrated damper. Damper caps and top mounted dampers often have a gasket that helps seal the opening, therefore they are generally more energy efficient than traditional dampers.

Direct Vent - A sealed combustion system that utilizes a flue pipe to draw air for combustion from the exterior of your home and a flue pipe inside of this pipe that exhausts combustion gasses outside. 

Draft - The rising gas creates a pressure difference called draft, which draws combustion air into the appliance and expels the exhaust gas outside through the chimney.

Draft Hood - The draft will change in a chimney as exhaust vents towards it, especially when going from cold air to hot. A draft hood is placed above the upper most part of gas appliances such as a furnace or water heater, to draw air into the chimney, creating a consistent air flow without any wind gusts or sudden temperature spikes or drops. Hot air, if not put through a draft hood would create a strong air flow through the burners. A draft hood significantly cools the air as it is released by the burners, causing condensation if the system is not calibrated properly.

Dryer Vent - A vent connected to a clothes dryer that is used to screen lint and remove exhaust.

Dryer Vent Cleaning - Dryer vent cleaning is a service in which the built up lint is removed from the dryer venting systems. Lint that normally occurs in a clothes dryer can build up over time. Build-up of lint causes the dryer to take more time in drying clothes and becomes a fire hazard.


Exhaust - The system through which waste gases are expelled.


Fireback - A piece of heavy cast iron, sized in proportion to the fireplace and the fire, which is placed against the back wall of the fireplace. Firebacks serve two main purposes; protect the back wall from damage that may be used by fireplace tools during use and to reflect heat back out into the room.

Firebox - Chamber of a fireplace or stove where the fire actually burns.

Firebrick - Brick composed of clay and silica and designed to withstand high temperatures such as those found in a firebox.

Fireplace - A place for a domestic fire, especially a grate or hearth at the base of a chimney.

Fireplace Grate - A frame of steel or cast iron bars for holding fuel when burning, as in a fireplace or stove. It provides a safe and secure foundation upon which the fire burns. The grate is positioned roughly in the center of the firebox and filters falling ash from the burning fire above, improves the quality of the flames produced and increases the heat output.

Fireplace Insert - Wood, coal, pellet, or gas heating appliances that fit inside an existing fireplace.

Flashing - Sheet metal or other materials used in waterproofing roof valleys or the angle between a chimney and a roof.

Flue - The passage in a chimney for conveying flue gases to the outside atmosphere.

Flue Collar - The flue collar is the round, metal opening designed for connecting vent piping. Any appliance that requires venting, including stoves and furnaces, has a flue collar where gases and smoke leave the appliance and enter the chimney flue. It is usually composed of metal and may appear on the top or on the back of the appliance. Some flue collars are designed to connect chimney inserts or stoves to the chimney.

Flue Liner - Special liner required by codes and standards to cover the inner surface of the flue. The liner serves as a buffer between flue gases and chimney walls and is designed to contain the products of combustion.

Flue Tile - A rectangular, square or round section of terra-cotta (clay) tube. Masonry chimneys have sections of clay flue tiles stacked one on top of the other to form a liner called the flue.


Gas Fireplaces - Fireplaces that have either been converted from wood to gas or were constructed for gas. Most often their primary purpose is atmosphere rather than heat.

Gas Insert - A gas burning appliance that burns propane or natural gas to create flames. Gas inserts are installed into an existing fireplace and are generally vented up through the existing chimney.

Gas Log - A gas-burning appliance consisting of a gas burner made to resemble a log, used in a fireplace to simulate the effect of a burning log.


Hearth - Floor area within the firebox of a fireplace or a fireplace stove.

Hearth Extension - A structure, usually consisting of stone, masonry or tile that protrudes into the living area of the house.


Mantel - The fireplace mantel or mantelpiece, also known as a chimneypiece, originated in medieval times as a hood that projected over a fire grate to catch the smoke. The term has evolved to include the decorative framework around the fireplace. Mantelpiece is now the general term for the jambs, mantel shelf, and external accessories of a fireplace. This is also often referred to as the fireplace surround.

Masonry Chimney - A field-constructed chimney of bricks, stones or reinforced Portland cement concrete, lined with suitable chimney flue liners built in accordance with applicable building code requirements.

Masonry Fireplace - A hearth and firebox of solid masonry units such as bricks, stones, listed masonry units, or reinforced concrete, provided with a suitable chimney.

Mortar - A mixture of lime, cement, sand, and water, placed between individual masonry units such as brick, stone and other materials, to bond those materials together.

Mortar Joint - In masonry, mortar joints are the spaces between bricks, stone and other materials, that are filled with mortar. Mortar joints can be made in a series of different fashions. The mortar that crates the horizontal joints between masonry units is called a Bed Joint. The vertical mortar joints are Perpend Joints, often referred to as head joints. The most common styles of mortar joints are: 

  • Concave joint - This popular type of joint is formed in mortar through the use of a curved steel jointing tool. It is very effective at resisting rain penetration due to its recessed profile and the tight seal formed by compacted mortar. Patterns are emphasized on a dense, smooth surface, and small irregularities are hidden.
  • V-joint - This type of joint can be made with a V-shaped jointer or a trowel soon after the bricks are laid. Ornamental and highly visible, the joint conceals small irregularities and is highly attractive. Like the concave joint, the V-joint is water-resistant because its formation compacts the mortar and its shape directs water away from the seal.
  • Weather joint - Mortar is recessed increasingly from the bottom to the top of the joint, with the top end not receding more than 3/8-inch into the wall. The straight, inclined surfaces of the bed (horizontal) joints tend to catch the light and give the brickwork a neat, ordered appearance. This joint is less compacted than the concave and V-joints, although it is still suitable for exterior building walls.
  • Grapevine joint - While most popular during America’s Colonial period, this design is often replicated in newer brickwork. It is created with a grapevine jointer, which is a metal blade with a raised bead that creates an indented line in the center of the mortar joint. These lines are often rough and wavy, simulating the generally straight yet slightly irregular appearance of a grapevine. It is commonly used on matte-finish and antique-finish brickwork.
  • Extruded (squeezed) joint - This joint design requires no tooling and is formed naturally as excess mortar is squeezed out from between the bricks. The result is a rustic, textured appearance. This design is not recommended for exterior building walls due to the tendency for exposed mortar to break away, degrading the wall’s appearance.
  • Beaded joint - Raising a rounded, bead-shaped segment of the mortar away from the mortar surface produces this old-fashioned, formal design. Although beaded joints can create interesting shadows, they are not recommended for exterior use due to their exposed ledges.
  • Struck joint - This joint is formed in a similar fashion as the weathered joint, except that the bottom edge, instead of the top edge, is recessed. It is a very poor insulator against water, as it will allow water to collect on its bottom ledge.
  • Raked joint - For this design, mortar is raked out to a consistent depth. Although often left roughened, it can be compacted for better water-resistance. This design highly emphasizes the joint and is sometimes used in modern buildings in order to match the historic appearance of their locales. Unless it is compressed, it is not as water-resistant as other mortar joints because the design incorporates ledges, which will collect water as it runs down the wall. Also, when mortar is removed from the joints, it becomes smeared on the surfaces of the brick at the recesses. To remove the mortar, contractors often aggressively clean the walls with pressurized water or acid solutions, which can open up additional voids and increase the possibility of water penetration.
  • Flush joint - This joint is best used when the wall is intended to be plastered or joints are to be hidden under paint. Because the mortar is not compressed, it is less water-resistant than some of the other designs.
  • Tuck pointing - This joint has mortar colored to match the bricks surrounding a line of white mortar to make the joints look very small. The white portion of the tuckpointed joint stands proud of the bricks.

Multi-flue Chimney - A single chimney containing more than one flue.

Multi-flue Cap - A chimney cap that covers more than one flue. Often a custom size, mounted to the flue tiles or the exterior edge of the chimney.


NCSG - The National Chimney Sweep Guild (NCSG) is a 501 (c) (6) non-profit trade association for Chimney Sweeps in The United States.


Parging - A thin coat of mortar applied to the inside of a masonry chimney or to the walls of a smoke chamber designed to reduce the resistance of flow in the chimney system.

Pellet Stove - A pellet stove is a stove that burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By steadily feeding fuel from a storage container (hopper) into a burn pot area, it produces a constant flame that requires little to no physical adjustments.

Pyrolysis - Chemical alteration of wood, coal, or other combustible materials as a result of the application of heat.


Reline verb - To add or replace pipe and insulation in an existing chimney flue that needs repair.


Seasoning - Wood drying (also seasoning lumber or wood seasoning) reduces the moisture content of wood before its use.

Smoke Chamber - Chamber in a fireplace directly above the smoke shelf and extending to the base of the flue.

Smoke Shelf - The area at the bottom of the smoke chamber created as the back wall of the firebox arches forward. The shelf is located at the intersection of the smoke chamber and the firebox. A damper is normally located on the forward side of the smoke shelf.

Soot - A black powdery or flaky substance consisting largely of amorphous carbon, produced by the incomplete burning of organic matter.

Stainless Steel Liners - Stainless steel pipe, either rigid or flexible, made for relining flues of masonry chimneys when the original clay liner has cracked or broken. May also be used to create a lining in a masonry chimney that was made without a clay liner.

Stack Effect - The tendency for warmer air to rise within a structure, creating lower pressure in the lower areas of the building.


Thermal Expansion - Alteration to temperature inside a chimney or duct system that causes the metal surfaces to expand.

Thimble - Fixed or removable ring, tube, or lining usually located in the hole where the chimney connector passes through a wall and enters a chimney or vent.

Throat - Opening above a fireplace firebox through which flue gases pass from the firebox to the flue. The fireplace damper frame assembly is usually located at the throat of a fireplace.


UL – Underwriters Laboratories - UL is a global safety consulting and certification company headquartered in Northbrook, Illinois. Established in 1894 as the Underwriters' Electrical Bureau (a bureau of the National Board of Fire Underwriters), it was known throughout the 20th century as Underwriters Laboratories and participated in the safety analysis of many of that century's new technologies. UL is one of several companies approved to perform safety testing by the U.S. federal agency Occupational Safety and Health Administration (OSHA). OSHA maintains a list of approved testing laboratories, which are known as Nationally Recognized Testing Laboratories.


Vent - A continuous passage (a pipe) from the flue collar to the draft hood where combustion gasses begin their expulsion from an appliance such as a furnace, water heater, or stove.

Video Scan - Incorporating a closed circuit video camera and monitor, for inspecting the interior of flues and other inaccessible areas.


Woodstove - A wood-burning stove is a heating appliance capable of burning wood fuel and wood-derived biomass fuel, such as sawdust bricks. Generally the appliance consists of a cast iron or steel, closed firebox, often lined by fire brick, and one or more air controls, which can be manually or automatically operated depending upon the stove.