Glossary of Terms

Airtight Heater

One in which the amount of oxygen entering into the firebox is totally controlled, allowing the fire to burn slower and thus last longer.


A design feature of Dutch West wood stoves, by which incoming combustion air enters the firebox above the front glass, and shields the glass from the flame, thus keeping it cleaner.


Two pieces of metal designed to support firewood in a firebox.

Ash Door

A door found in the floor of the firebox that provides access to the ash dump, through which ashes can be dumped into the ash pit.

Ash Pit

A storage compartment for ashes, located in the chimney base.


A near-horizontal metal panel, usually at the top of the inside of the firebox, which deflects the gases and smoke so that they stay in the firebox longer, resulting in more complete combustion. Scandinavian stoves have a special baffle system that causes the logs to burn back to front.


The area located above the damper on the front smoke chamber wall of a masonry fireplace.


The initials stand for British Thermal Unit(s). This is an outdated but commonly used measure of heat, and is the amount of heat required to raise the temperature of one pound of water 1ø Fahrenheit. 3,412 BTUs is equal to one kilowatt-hour (1kWh). Suppliers should be able to supply heat output in kilowatts (kW).


This is an outer shell for the firebox, which permits a greater diversity of finishes, such as tile surfaces. The cabinet helps to reduce the surface temperature of the stove (especially important if there are small children around the house) and reduces the distance necessary from combustible materials and surfaces. Cabinet stoves provide a greater volume of convective heat.

Cast Iron

A metal commonly used for wood heaters, cast iron is an alloy of iron, carbon and silicon that is poured into a mould made from a master pattern.

Catalytic Converter/Combustor

A catalyst is something that increases the rate of chemical reaction without taking part in it. In stoves, they are usually a ceramic substance coated with metal. They increase overall efficiency and reduce creosote production and smoke emission (which is particularly useful in areas with high air pollution potential). Nevertheless, check their lifetime, risk of damage and replacement cost.


An enclosure for a “Class A” or factory-built chimney which hides the metal chimney from view.


One or more passageways, vertical or nearly so, for conveying flue gases to the outside atmosphere

Chimney or Flue Cap

A factory-fabricated appliance that is installed on the chimney top to protect the chimney from water intrusion, birds, leaves and other debris.

Clean Out Door

An door located on the exterior base of the chimney which provides access into the ash pit for the purpose of removing ash.


The distance required by building and fire codes between stove, smoke pipe or chimney and combustible materials such as wood furniture or carpets. Clearances must be obeyed even if the combustible materials, such as wood furniture or carpets, are protected by noncombustible plaster or other masonry materials.


The process of burning, or oxidation accompanied by heat. When sufficiently rapid, also accompanied by light.


Chimney and stovepipe deposits originating as condensed wood smoke having three stages. 1st stage is soot, 2nd stage is lumpy and crisp, 3rd stage looks like roofing tar and is smooth as glass.

Convection Heating

The natural movement of air as it heats up and expands. This creates a natural flow of air as the warmer air moves upward and is replaced by cooler air.


A measure of firewood, equal to an amount measuring 4 feet x 4 feet x 8 feet.


A moveable blade located in the throat of the fireplace. Designed to impede air flow into the chimney.


The difference in air pressure at the same elevation between the inside and the outside of a chimney, chimney connector, or appliance. The term draft is sometimes used to denote the rate of combustion airflow into a fuel burning appliance, or the rate of flue gas flow. Draft is a critical component of stove or fireplace performance.


Energy efficiency is the fraction (or percentage) of the energy in the fuel that becomes heat in the house, i.e. heat energy output divided by solid fuel energy input. Efficiencies of slow combustion heaters vary from model to model, and during various operating conditions and use of different fuels. Do not confuse efficiency with effectiveness.


byproducts of combustion vented out of the home.


An opaque vitreous compound applied by fusion to the surface of metal. Heaters with an enamel finish are easy to maintain because they do not need to be painted or blackened.

Energy Efficiency

The percentage of the total energy content of the fuel consumed that becomes useful heat in the house.


The area that contains the grate or andirons upon which the materials are arranged for combustion.


Heat refractory brick used in the construction of a firebox.


Hearth, firebox, fascia and chimney.


Sheet metal used to make a water-tight seal between the chimney and the roof.


The passage in the chimney which moves the products of combustion up and out of the chimney top.

Flue bypass

A damper-type plate situated within the firebox which, when closed, forces the volatile gases into a secondary combustion chamber.

Flue Cap

See Chimney Cap.

Flue Liners

Materials that add protection to the inside of the chimney, protecting it from intense heat.

Freestanding Heater

A heating appliance normally on legs or a pedestal that occupies an area roughly equal to that of an easy chair.


Sheet metal or steel thickness is measured in terms of gauge. The lower the gauge number (e.g. 24, 18) the thicker the metal (although sometimes thickness of sheet metal in a stove is stated in fractions of an inch or in millimeters). Gauge is usually used to describe flues.


Raised grid-like metal structure where fuel is placed in the firebox.

‘Green’ wood

Wood that has just been cut from a live tree, or wood that has not partly seasoned at least.

Hardness of wood

The denser and heavier the wood and the harder it is, the better it is for firewood. Most pine is soft wood. Hard wood will burn longer, leave less ash, and usually spark and smoke less than soft wood.

Hearth (Inner)

The floor of the firebox.

Hearth (Outer)

The area in front of the firebox opening which is constructed of non-combustible material.

Heat Exchanger

Usually a chamber at the top of the fire box that is heated by the burning of the volatiles. Heat in this chamber is either vented into the room by convection or the use of a fan.

Heat Shield

A heat-resistant material, either anchored to the rear of a free-standing slow combustion heater or attached to walls with airgaps (between heat shield and wall), permitting the heaters placement closer to heat sensitive walls.


A container attached to an appliance in which fuel, either coal, nuggets or wood pellets, is stored and from which the fuel is fed to the burner.

Inbuilt Heater

A model which fits into an existing fireplace, with the flue going up through the chimney. Other types, with special insulating cabinets, can penetrate existing combustible walls. On some of these units a fan (usually two-speed) propels the heated air into the room. Other inbuilt heaters are designed to operate efficiently without a fan. ‘Back-to-back’ and ‘two-way’ units are also available if heat is required in two rooms separated by a solid wall.

Island Fireplace

A fireplace that has four sides of glass, for viewing from any angle.


Small pieces of very dry wood that, when mixed with newspaper, will ignite fire logs.


The metal bar or other non-combustible material that spans the top opening of the firebox.


an ornamental facing surrounding the fireplace or simply a shelf above a fireplace.

Negative Pressure

Condition in a building where the inside pressure is less than the outside pressure. This is often caused by kitchen fans that draw inside air out of the house, and it can effect stove or fireplace performance.


This means to coat or to spread. Typically mortar parging is found in the smoke chamber of a newly constructed fireplace.

Particulate Matter

pollution produced from various sources including woodsmoke. Fine particle pollution (PM 2.5) is invisible to the naked eye and can be inhaled deep into the lungs.


Chemical alteration of wood, coal, or other combustible materials as a result of exposure to heat.

Pellet Stove

A kind of stove that burns wood fibers that are compressed into the size of a pencil eraser.


Are made of 100% wood sawdust with no additives. The sawdust in pellets is a manufacturing byproduct otherwise destined for landfills.

Peninsula Fireplace

A fireplace that has three sides of glass.

Primary Air

Combustion air directed to the firebox where the fuel is located; supports all stages of combustion.

Radiant Heat

A kind of heat, by which objects are heated (and not the air around them).

Seasoning of wood

Seasoning is the gradual reduction of the moisture content of ‘green’ wood. If ‘green’ wood is stored under proper sheltered conditions, with reasonable air circulation, for nine months to a year, it’s moisture content will reduce from about 50% by weight to about 20%, when it is then suitable to burn. Completely dry wood is possible only under laboratory conditions.

Secondary Air

Air drawn into a wood stove firebox at a strategic point to ignite wood gases, enabling more complete and efficient combustion.

Secondary Combustion

The burning process of volatile gases in specially-designed wood heaters. Without secondary combustion, these gases escape, unburned, up the chimney.

Secondary Combustion Chamber

An upper cavity at the top and rear of the stove, intended to take the place of a baffle.


A fine black, powdery substance formed by chemical breakdown in the combustion of wood.

Steel or Sheet Metal

An iron material distinguished from cast iron primarily by it’s lower carbon content and the fact that it is much more malleable. There are many grades and gauges of this type of metal. Steel plate (as opposed to steel sheet) permits full welded construction, which increases stability and durability.

Smoke Chamber

The section of a masonry fireplace that contains the smoke chamber walls and the smoke shelf and located above the throat or damper area and below the flue.

Smoke Shelf

A shelf located behind a fireplace damper.

Solid Fuel

Wood or coal.

Spark Arrestor

A wire cage that is installed on the chimney termination to prevent sparks from moving into the atmosphere.


An opening just above a fireplace. The damper is usually located in the throat of a fireplace. Top Sealing Damper- A device installed on the chimney top which will impede the air flow.

Wash Crown

Concrete piece on the top of a chimney which seals off the air space between the inner walls of a masonry chimney and the flue liner. It slopes away from the liner to shed water.

Woodburning Appliance

Any fireplace, wood burning heater, or pellet-fired wood heater, or any similar enclosed device burning any solid fuel used for aesthetic or space-heating purposes, which has a heat input of less than one million British thermal units per hour.

Woodburning Heater

An enclosed, wood burning appliance capable of and intended for space heating (i.e. a wood stove or fireplace insert).


A wall of bricks that separates two or more flues in a chimney. Typically this is an unlined flue. Zero-Clearance Fireplace