Glossary of Chimney-Related Terms



AL29-4C is an alloy of stainless steel that is highly resistant to corrosion, used for relining flues that will vent a modern, high-efficiency gas furnace. Since most of the heat generated by such an appliance goes into warming the home, flue gas temperatures tend to be relatively low. Low flue gas temperatures keep moisture in the flue gasses from evaporating and being eliminated up the flue. This combination of moisture in the flue gas, along with other chemicals that may be inducted into the flue from the surrounding environment, can contribute to a very corrosive flue gas composition. AL29-4C is made to resist such corrosive environments over a long period of time.


Located on the floor of the firebox, this door allows you to easily sweep the ash from your firebox, into the ash pit below, and accessible for cleanout by means of a cleanout door



The boot adapter transforms stoves or fireplace inserts oval or rectangle exhaust openings to round exhaust openings. This will allow a round liner to attach directly to the appliance. The adapter collar angles back to give it a smaller profile. The collar can also be changed to a 30 degree or 10 degree tilt.



Carbon monoxide (CO) is an odorless, colorless, tasteless poisonous gas that is a by-product of incomplete combustion. Sometimes an early warning is flu-like symptoms, but CO can cause brain damage and death with no warning. A damaged furnace flue poses a real threat of carbon monoxide poising, because this gas can escape through the smallest crack. Also a partial or complete collapse of the clay flue liner can block the flue, and quickly fill the house with deadly gas. This tragedy occurs in homes every year. Estimates indicate that 55,000 reported incidents happen in homes alone.


A chase is a wood-constructed chimney. It has a decorative surrounding that covers the multi-wall insulated metal flue inside the chimney. The box is typically covered with vinyl, aluminum or wood siding, or sometimes simulated stone.


The chase cover covers the entire top of your chimney/chase to prevent rain and snow from entering. It is not recommended you install a galvanized chase cover. Galvanized covers rust fairly quickly and will leak. Stainless steel is the most widely used, with Copper for those that want a more elegant look.


A self-standing outdoor fireplace, with a large round fire chamber open on one side and a vent stack (chimney). These are used year around and typically found on back patios, decks or in garden sitting areas. They provide for easy starting, efficient burning and great heat. They are made from a variety of materials, but cast aluminum seems to be preferred by most, for its heat output, light weight and strength.


A structure made of masonry or metal, that usually surrounds and supports the flue for venting hot flue gases or smoke from a fireplace, furnace, stove or insert to the outside atmosphere. Chimneys are typically vertical, to ensure that the gases flow smoothly.


Protective coverings for chimneys usually made of stainless steel, or copper. Most chimney caps have a mesh screening that serves the dual purpose of spark arrestor and barrier against animals. Chimney caps prevent rain from entering the flue of the chimney, and help prevent down-drafts.


This is the process of removing soot, creosote, and debris from a chimney. This should be done on a regular basis in order for the chimney to operate as efficiently and safely as possible, and to maintain your warranty if you have a stainless steel liner.


A log impregnated with chemicals which when burned in a fireplace is said to loosen creosote and soot in the flue and allow them to fall into the firebox. It is generally believed this is not a safe substitute for a physical cleaning of the flue by a chimney professional. Also known as chimney sweep log and chimney sweep fire log.


Devices, such as brushes, scrapers, and rods used for the purpose of cleaning chimneys, used by professionals and the "do-it-yourselfer".

CHIMNEY LINER also see flexible or rigid

A flue liner in a masonry chimney is clay, ceramic, or stainless steel installed inside of a chimney, intended to contain the combustion products, direct them to the outside atmosphere, and protect the chimney walls from heat and corrosion. Safe, serviceable flues must remain free of perforations, cracks or damage of any kind that could allow carbon monoxide to pass into the living spaces of the home. A flue must also protect nearby combustible materials such as framing, walls, ceilings, insulation, or floors from the heat and smoke.


Chimney relining is the most practical and affordable way to repair deteriorated or damaged chimneys. Installing either flexible stainless or rigid stainless liners seems to work for most all applications. Chimneys can be damaged by a number of things such as settling, hurricanes and lightning, but the most common source of chimney damage is a chimney fire. In addition to chimney damage, older chimneys may be unlined or their liners may have deteriorated to the point where relining is warranted.


A group of professionals who make their living cleaning, inspecting, repairing and maintaining chimneys.

CLASS A INSULATED PIPE also see multi-wall

Class A chimney pipe, is made of double-wall or triple-wall insulated pipe, which is one pipe contained inside another. The goal is to minimize the outside diameter of the pipe and the allowable distance from combustibles. The outer wall of chimney pipe is stainless steel or galvanized steel. The inner wall is stainless steel. In three-wall pipe the intermediate wall is aluminized steel.


Devices installed in a masonry chimney to allow access to the interior chimney for the purposes of inspection, routine sweeping and creosote removal, or removal of debris. They can be made of steel, cast aluminum, or clay.


Burning wood and fossil fuels at low temperature causes incomplete combustion of the oils in the wood, which are off-gassed as volatiles in the smoke. As the smoke rises through the chimney it cools, causing water, carbon, and volatiles to condense on the interior surfaces of the chimney flue. This leaves a black oily residue referred to as "creosote".


A hand tool device used to reduce the opening of a rigid liner or component end (male) so it can fit into the end of the same size pipe.

CROWN (or Cap, Wash, Splay)

The chimney crown is usually a concrete piece at the top of the chimney, with a small gap around the clay tile (if installed) for expansion. The cement crown slopes away from the flue to deflect water.



Wood-burning fireplaces usually have a damper installed in the upper part of the firebox. The damper is designed to be shut when the fireplace is not in use and can be easily opened when it is. It's common to forget to close the damper after a fire goes out, however, and that leaves a big hole through which heated or cooled air can escape the house. Even when a fireplace damper is closed, the sealing is often not very effective.


Chimney dampers with caps are mounted to the top of the chimney, replacing traditional throat dampers, with caps to protect them from weather. These top dampers also prevent unwanted air intrusion down the chimney, and keep warm air from escaping when the chimney is not in use.



An electric fireplace is an electric heater that mimics a fireplace burning coal, wood, or natural gas. Electric fireplaces are often placed in conventional fireplaces, which can then no longer be used for conventional fires. They plug into the wall, and can run on a "flame only" setting, or can be used as a heater. An electric fireplace is a kind of vent-less fireplace, which is a type of fireplace that does not require a ventilation system.



Fire glass is a product which is designed to be used in gas fireplaces or gas fire pits to help reflect the light and heat, and can replace the lava rocks or fake logs. The fire glass is available in a variety of shapes, colors and textures to allow you to design a one of a kind look. Fire glass does not melt or emit toxic fumes, smoke or soot, and lasts virtually forever.


A masonry fireplace has a firebox built of individual, generally yellowish firebrick. The firebox, of course, takes the brunt of the fire's heat and it requires some special attention. The firebrick can take the heat pretty well, but the joints will fail in time from the constant expansion and contraction. In a fireplace without a chimney cover, rain water will also pool on the smoke shelf, mix with the soot behind the damper, and form acidic slurry that seeps into the fire back destroying the mortar joints. These joints must be kept in good repair with a high temperature refractory mortar to ensure the fire is contained.


Referred to as refractory brick, used to line the fire box area, inside stoves, inserts or fireplaces. These brick can withstand extremely high temperatures. Firebricks can be purchased as individual brick, or in a panel and can be cut to size. In a fireplace application they should be set with refractory cement.


A round enclosure for containing a fire outdoors. The fire pits of today have changed dramatically with their elevated stands and styles, some of which transform into tables. They can be wood burning or converted into gas burning.


A device of either metal or masonry construction open on at least one side, designed to contain a fire. These can be for outdoor use such as cooking and barbeque, or for indoor use for ambiance and some heat.


These liners are round, and can be reshaped to oval, square or rectangle, to fit most all applications. When installed in a brick chimney they will follow the path of the flue through turns or offsets. They are corrugated on both inside and outside to allow for flexibility. Smooth wall flexible liners are smooth on the inside only, and are only available in round and will have about 20% better draw. See also chimney liner.


A flue is a duct, pipe, or inner portion of a chimney used for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. Flues are typically made of clay tiles or metal. Safe, serviceable flues must remain free of perforations, cracks or damage of any kind that could allow carbon monoxide to pass into the living spaces of the home. A flue must also protect nearby combustible materials such as framing, walls, ceilings, insulation, or floors from the heat and smoke.


The main function of a flue extender is to add height to the existing chimney to increase draft. Taller chimneys will provide better draft and increase performance to the appliance, and usually add 18" to 36" in height. The other added benefit is that many of the extenders can add a decorative appearance to your chimney, and some will be used as a chimney cap.



Artificial logs made of ceramic or fiber used in conjunction with a burner fueled by natural or liquid propane gas to simulate wood burning.


Fireplaces that burn gas instead of wood as fuel. These may have been converted from wood to gas or constructed specifically for gas. Frequently their primary purpose is ambiance and aesthetics rather than heat.


Heating or cooking appliances that use natural gas or liquid propane as their fuel.



The area directly in front of the opening of the fireplace, usually constructed of masonry or other heat resistant material for the purpose of shielding the floor from excessive heat.


A heating device that returns to the heating environment more than 84% of the heat it generates. Such a device has, therefore, relatively low flue gas temperatures. The lower flue gas temperatures result in more moisture that condenses on the interior flue walls. This situation significantly increases the opportunity for corrosion within the flue.



An insert is basically a fireproof box that's surrounded by steel or cast iron and fronted by insulated glass, and is inserted into an existing fireplace opening. Some inserts have a blower that pushes the hot air back into the room through front vents Fireplace inserts are much more efficient than a traditional fireplace. Inserts can be powered by electricity, gas, propane, wood, pellets or coal.


Material inserted between the stainless liner and chimney wall to keep the flue gases warmer inside the liner. The insulation can be a blanket wrap kit or a pour down mixture of water and vermiculite substance. Blanket wraps will add approximately 1.5" to the overall diameter of the liner, where the pour down mixture is usually used where there is less clearance. Insulation is not required, but is highly recommended. The warmer the gases are the better draft will be created. A better draft means less creosote and greater efficiency with the appliance.



A heating device that returns to the heating environment less than 84% of the heat it generates. Such a device has a warm enough flue gas temperature to allow for the vaporization and release to the environment most of the moisture created in the combustion process. This allows for a flue gas environment that is substantially less corrosive than that created by a high-efficiency gas furnace.



Sometimes referred to as a mantelshelf, usually covering part of the chimney above a fireplace opening, typically used in a decorative manner. It can also be designed to divert heat from rising directly up the wall.


A chimney cap designed to attach to the crown of a chimney and cover more than one flue on the same chimney.


Rigid insulated pipe with double or triple walls used for close proximity of combustible materials as in a chase or through a ceiling, attic, roof or wall.



That portion of a chimney located between two completely vertical portions that bends away from the vertical for architectural reasons. This bend can be as much 45 degrees. Offsets in chimneys are often difficult to negotiate when relining a chimney with rigid stainless steel relining pipe. That's why flexible relining pipe is so often used in the relining process.


This two piece adapter / off-set box is designed to allow you to adjust the amount of offset between the insert exhaust and the liner, up to 6".



A pellet stove or pellet insert burns compressed wood or biomass pellets to create a source of heat for residential and sometimes industrial spaces. By slowly feeding fuel from a storage container (hopper) into a burn-pot area, they create a constant flame that requires little to no physical adjustments. They are extremely efficient appliances compared to wood burning appliances.


Pulling cones are used to assist in the installation of a stainless chimney liner around the hard to maneuver twists and offsets by attaching a rope or winch to the eyelet and guiding it through the flue.



See chimney cap.


Refractory cement is made with high temperature cements and aggregates that will not expand when heated. This cement is used when building or repairing fireboxes, smoke chambers and flue liners.


Non-flexible stainless steel pipe used for relining masonry chimneys. Used primarily in chimneys that are straight with no offsets. Sizes range from 6" to 48" lengths and 3" to 16" diameter.



A chimney cap designed to attach to or cover a single clay tile flue.


Typically between the throat damper, and flue. The function of the smoke chamber is to take the exhaust gases from the large firebox and direct them into the relatively small chimney flue. The goal is to gently compress the exhaust gases without creating back-draft. The tapered walls, from the firebox to the flue will allow the gases to draft quickly and completely. If it works well, it accelerates the exhaust gases up into the chimney and helps to promote good draft. If not, the result is smoke in the house.

Factory-built fireplaces do not usually have a smoke shelf or smoke chamber above the damper. Since most of these fireplaces draw quite nicely, the need for a smoke shelf is questionable. It is, however, a standard part of most masonry fireplaces.


This is part of the smoke chamber area, located behind the throat and flue. It has two purposes: first, the ledge will catch water and debris and second, the ledge at the bottom of a smoke chamber is designed to deflect or break downdrafts from the chimney.


The horizontal protruding portion of a tee connector is called a snout. Snouts are typically 10" in length but can be increased to 22" or longer if needed. There are also slip connectors that can be used as adjustable snouts. Most snouts are installed with a long looping clamp. A double snouted tee can be custom fabricated when two appliances are being vented into the chimney using two separate holes.


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


Stove pipe has a very specific application, in that it connects a free standing wood stove to the chimney, through a combination of elbows, tees and pipe lengths. Stove pipe cannot be used as a chimney system (inside walls or attic, or outside of the building) and it cannot be used inside a masonry chimney as a chimney lining system. It is recommended that the crimped male end of the pipe is always pointed downward to prevent creosote from dripping outside of the pipe. Single wall and double wall stove pipe is available, with double wall allowing you to reduce the clearance to combustible material.



Clay (terra cotta) tiles are the most common type of masonry chimney liners. They perform quite well for open fireplace chimneys that are properly maintained. There are two disadvantages to clay tiles. The first is that, being a ceramic product, they cannot rapidly absorb and evenly distribute heat during the rapid temperature rise that occurs during a chimney fire. This uneven heating produces an unequal expansion which in turn causes the flue tiles to crack and split apart. A chimney with cracked chimney liners must be repaired before use. The second disadvantage is that tiles cannot adequately contain the liquid combustion byproducts produced by modern gas appliances.


A thimble allows you to pass a single wall stove pipe from the living area or basement through the combustible material of a wall and into a brick or metal chimney. The thimble reduces the amount of clearance needed from 18" to 2".

THROAT DAMPERS also see Dampers

Metal plates installed just above the firebox of a masonry chimney that are used for sealing the flue shut when the fireplace is not in use. Since they seal metal to metal, the seal is quite leaky even when the plates are new. Over time, the plates rust and deteriorate as they are exposed to heat and moisture. When this happens they lose almost their entire flue sealing capacity.


A top plate fits on the top of a chimney to support a stainless liner, and provide an area to securely attach the rain cap to a flexible liner. There are three designs. The flat top will fit securely on any flat or semi flat surface, the No Sag that is tapered to prevent standing water and will not sag with the weight of a liner, and the Terra Cotta style that fits over the flue tile protruding out of the chimney. All three styles will completely cover the flue opening and only allow gases to escape through the center hole.


A device installed at the top of a chimney for the purpose of sealing the flue shut when the fireplace is not in use. They are often used as replacements for throat dampers that are installed just above the firebox when a masonry chimney is built. They are operated with a pull cable and will completely close off your flue preventing the loss of heated or conditioned air, unlike the standard throat damper. Lyemance and Lock-Top top-sealing dampers are as much as 90% more efficient than throat dampers because they provide a silicone rubber gasket seal rather than metal to metal. These dampers can also have a screened cap to prevent debris and animals when left open. They are not recommended for gas appliances.



Vent or draft fans are designed to help create draft and assist in moving the smoke and gases up the chimney. They are available either top mounted or in line with the pipe.


Fireplaces that do not need to vent products of combustion to the outside environment. All electric and some gas fireplaces fall into this category.



Enclosed appliances, most commonly constructed of steel or cast-iron, used for burning wood for the purpose of heating an indoor space.

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Our 316Ti flexible chimney liner and chimney liner components have passed the rigorous testing at the Underwriters Laboratories with best in class status and are UL Listed. So if you are looking for UL listed chimney liner sold directly to homeowners, then look no further than Rockford Chimney

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