WOOD - SLOW COMBUSTION
A Wood-Burner's Glossary:
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 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 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 This is an outdated but commonly used measure of heat, and is the amount of heat required to raise the temperature of one pound of water 1 Fahrenheit. 3,412 BTUs is equal to one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.
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.
Creosote: A complex oily substance formed by solid fuel combustion and deposited in the flue by the smoke and gases of the burning fire. It may appear as black sooty material or as tarry residue. Under certain circumstances, it will also liquefy. Flues should be cleaned regularly to avoid creosote build-up that could cause fires.
Damper: The draught-regulating mechanism on a flue, near where it leaves the stove vent. It is usually a round plate which revolves on a pin. In case of flue or chimney fire, it is important to be able to close this damper.
Efficiency: 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.
Firebrick: A special, high-heat resistant brick that is used to line the firebox, which protects it from direct contact with the flames, lengthening it's life. Firebricks are usually set in place, without cement, and must be replaced when they deteriorate (usually after three or four years of constant use).
Flue bypass: A damper-type plate situated within the firebox which, when closed, forces the volatile gases into a secondary combustion chamber.
Flue pipe: The fire-resistant pipe through which smoke and gases are carried to the outside. The part inside the room must be stainless or vitreous enamelled steel. For the section through the roof space, the flue pipe must be shielded by one or two cases, usually made of galvanised steel, forming insulating airgaps, or gaps filled with insulating materials. Copper or brass casings are sometimes used for decorative purposes and can act as heat-shields.
Gauge: 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 millimetres). Gauge is usually used to describe flues.
'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: A non-combustible surface (such as concrete, ceramic tiles, slate, or bricks) onto which the slow combustion heater is placed. The hearth should extend beyond the heater on all sides and at least 300 mm beyond the heater's opening. Depending on the thickness of the hearth, airgaps between the hearth and the floor are desirable for continuous air flow.
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.
Inbuilt Slow Combustion 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.
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 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.
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 Shelf: See baffle.
Stepstove: A stove with a two-step top to provide two cooking areas with varying surface temperatures.
Thermostat (automatic): Different materials are used, although a bimetallic strip or coil is common. After the stove's operater sets the thermostat for the heat desired (i.e. the temperature, which the fire burns) the thermostat controls the air input to the fire. As long as fuel is available in the firebox, the stove does the rest, increasing or decreasing it's heat production as required.