• Delivery to Store
  • No Minimum Order
  • Free Delivery on Orders over £50
  • Prices include VAT

You are here

Log Glossary

Logs2U Glossary

For general help, please use our Logs FAQ's or if you are not sure which are the best logs to buy for your appliance read our Log Buying Guide.


The non-combustible, mineral content of biomass. During combustion bottom ash is the ash that is left behind in, or under the grate. Fly ash consists of very small particles of ash that are carried out of the system along with the flue gases. Both types of ash can be used in moderation as a soil conditioner.

Also a species of tree, which is a very popular firewood as it gives a good combination of flame, heat and firelife.


Material that is derived from living, or recently living biological organisms. In the fuel context it is often used to refer to plant material, however by-products and waste from livestock farming, food processing and preparation and domestic organic waste, can all form sources of biomass. With such a wide range of material potentially described as biomass, the range of methods to process it are equally broad.A typical example would be biomass wood pellets .

Biomass Fuel

A solid, liquid or gaseous fuel that is derived from biomass. Biomass that has been processed or converted in some way into a more convenient form, principally to increase energy density. This may involve physical pre-processing simply to cut it into more manageable pieces or reduce the moisture content.


A small block of compressed material moulded by mechanical means into the desired shape.  Common briquetted materials used in fuel production include coal dust, charcoal, sawdust or woodchip.

Carbon Cycle / Carbon Neutral Process

The cycle by which carbon in various forms moves between the various components of the Earth's biosphere, between the atmosphere, hydrosphere (seas and oceans), lithosphere (rocks, soils and mineral deposits, including fossil fuels) and biological material including plants and animals. Carbon is constantly moving between some of these forms, maintaining a state of dynamic equilibrium. Other forms, most notably fossil fuels, can potentially store carbon indefinitely, however if they are burned the carbon is released and makes a net addition to the carbon cycle and raising the total free carbon. If biomass is used without replacement, as for instance can happen in the case of forest clearance such as in the Amazon rain forest, this too can make a net addition to the carbon cycle. Sustainable use of biomass, however, makes no such direct net addition as growing replacement plant material absorbs the carbon released by the harvested biomass, and is thus said to be a Carbon Neutral Process.

Calorific Value

The Calorific Value of a fuel is a measure of the amount of heat, per unit of weight that is produced when the fuel is burnt.  Usually expressed as Kilojoules / Kilogram (kJ/kg).

Closed Appliance

Term used to describe all heating and cooking appliances that have a closed fire chamber.  Includes wood-burning and multi-fuel stoves, room-heaters and cookers.

Dumpy Bag

A bag used for transportation of logs and other materials.  Come in a variety of sizes.  All Logs2u Dumpy bags are 1m3 bags with a special water resistant coating and top cover to ensure that all logs remain dry during transportation.

Energy Density

The amount of energy stored per unit volume (volume energy density) or mass (mass-energy density) of a fuel. A high energy density generally makes storage and transport of a fuel more convenient. Fossil fuels typically have higher energy density than solid or wet biomass fuels.  The energy density of logs can be increased by reducing the moisture content of logs .

Energy Output

The amount of energy released, measured in KiloWatt Hours (KW/h) when burning fuel.  For logs this figure depends on the moisture content of the wood.  The lower the moisture content the more energy will be released.


A Firelog is a manufactured log constructed to be used as wood fuel. Firelogs are designed to be inexpensive while being easier to ignite and burn longer than firewood. Firelogs available from Logs2u are manufactured using sawdust and paraffin, which is mixed and extruded into a log shape. The extruded firelogs are individually wrapped in paper packaging which can be ignited to start burning the firelog as the paraffin is readily combustible.


Firewood usually relates to timber or trees unsuitable for building or construction. Firewood is a renewable resource provided the consumption rate is controlled to sustainable levels.

Green Wood

Wood that has been recently cut and which has not had an opportunity to season.  Green wood can have a moisture content as high as 60%.  When burnt, green wood uses much of its energy to evaporate off the moisture it contains and therefore, does not produce as much heat as seasoned or kiln dried wood.  Because of the lower temperatures, larger amounts of Tar are produced which are deposited on exhaust flues leading to fouling of the system.  Green wood should never be used on closed appliances, but can be used on open fires.


Wood from broad leaf deciduous trees, such as oak, maple, ash, beech or poplar.  Hardwoods tend to be denser than softwoods and therefore have higher calorific values, meaning they will generally burn hotter and longer than softwoods. Logs2U supply oak, birch, alder and beech hardwood logs.

Kiln Drying

A process where cut logs are dried under controlled conditions of heat, humidity and air circulation to accelerate the natural wood drying process.  The moisture content of logs can be accurately controlled and standardised from one batch to the next.

Kiln Dried Logs

Logs that have been dried in an oven to reduce their moisture content to less than 20%.  Kiln dried logs are recommended for use on closed appliances such as wood burners, multi-fuel stoves, and ovens as they produce much less tar, which if allowed to build up will foul your system.


Refers to the material or materials used to start a fire. In Logs2u's case, it specifically means the short sticks of wood used to get a fire started.

Log Splitter

Sometimes known as a Splitting Maul.  It is a heavy, long handled tool used for the splitting of logs along their grain.  Please see our Real Wood Guide for an explaination of how to split logs.

Log Store

A structure, usually wooden, used to stack and store logs where they are protected from rainfall but which allows fresh air to circulate.  A log store provides the ideal place to season green logs or to protect seasoned or kiln dried logs from the elements.

Mixed Wood

Usually refers to a delivery of wood, indicating that the wood is a mixture of different species, with possibly both hardwood and softwood varieties.

Moisture Content

The proportion of water in logs (including sap), defined as the weight of water as a percentage of the weight of the logs. This can be defined on either a wet basis, as a percentage of the total (wet) weight of the sample or a dry basis, as a percentage of the oven-dry weight of biomass. Wet basis is usually used for fuel purposes.

Seasoned Logs

Seasoned Logs have been naturally seasoned over time until such time as their moisture content has reduced to between 25-30%.  Seasoned logs have a higher moisture content than kiln dried logs and will therefore not burn as hot.  Seasoned logs are suitable for use in a range of appliances and open fires - Read our Log Buying Guide for key attributes.


Wood from conifers (coniferous trees) such as pine, spruce and fir trees.  Much more common than hardwoods and because they are easier to work with used extensively in constuction, furniture and paper manufacture.  However, they are generally less dense than hardwoods and do not burn quite as hot or for as long.


An enclosed cooker or heater, used to burn fuel for the heating of a room or the cooking of food.


The common name for the resinous partially combusted material produced by the burning of logs.  Tar is produced by the natural sap in the wood and can build up in stoves and flue ways over time.  The lower the moisture content of the logs being burnt, the less Tar build up will occur.  This is because logs with low moisture content, have less sap in them to begin with and as they burn hotter the tar is burnt off more efficiently.


Woodchips are an alternative solid fuel for heating in buildings or power generation.  They are generally low in cost, but there are few if any residential systems that can burn this fuel type efficiently enough to realise these cost benefits.  There use is generally restricted to larger commercial heating requirements such as schools, hospitals or office buildings. Please note that wood chips are not the same as wood pellets.

Wood Fuels

Wood fuel is any wood based product used as fuel and includes logs, wood pellets, woodchip and wood briquettes.

Wood Pellets

A type of wood fuel, generally made from compacted sawdust. The pellets are extremely dense and can be produced with a low humidity content (below 10%) that allows them to be burned with a very high combustion efficiency. Their regular geometry and small size allow automatic feeding and their high density also permits compact storage and rational transport over long distance. Wood pellets  can be conveniently blown from a tanker to a storage bunker or silo on a customer's premises. As the price of heating with fossil fuels increases, more capacity for pellet heating has been installed.

The one draw back is that specialist pellet burning stoves must be used which can be very expensive compared to other types of appliances.  However these stoves offer a number of benefits in terms of heating efficiency, ability to run for extended periods with little operator intervention, 24-hour thermostatic control, low levels of ash and low maintenance.

Wood Seasoning

A naturally occurring process that starts once a tree is felled, whereby the wood starts to dry out through evaporation of the internal moisture.  Wood seasoning can be accelerated by laying down the wood under cover from rainfall, such that air can circulate between the logs.  Newly felled wood can have a moisture content as high as 60%.  Depending on the ambient temperature seasoning to 25-30% moisture (suitable for closed appliances) can take between 1 and 2 years.