Fuel Choices & Performance
There are a number of different solid fuels available for burning on open fires and stoves, of which the most commonly used are wood and coal (including smokeless coal). When choosing your fuel there are two important factors to consider:
The type of fireplace or appliance you are using – Some appliances are designed to only use specific fuels, you can’t just burn anything in them. It’s important to follow manufacturers instructions regarding which type of fuel to use. Whether or not you are in a Smoke Control Area – There are 5 Smoke Control Areas in Brighton with restrictions on the type of appliance you can use and fuel you can burn.
The sections below include information about burning wood, coal and other materials often picked up from skips or from left over building work. There is a list of the common types of wood available in the UK and details of it’s burn quality and also information about what to burn in stoves. If you have feedback regarding your experiences, please Contact Us.
Is Wood Carbon-Negative?
Carbon dioxide (CO2) is a ‘greenhouse gas’ and the main pollutant responsible for the process of global warming, as it traps the suns heat so increasing the temperature of the earths surface. Over the last 150 years we have pumped enough CO2 into our atmosphere from the use of fossil fuels in coal, oil and gas fired power stations, not to mention aircraft and the more than one billion cars in use today, to raise CO2 levels higher than they have been for hundreds of thousands of years.
Burning wood is considered to be the most environmentally friendly form of heating using combustion and one of the most energy efficient when burned in a wood burning stove. The amount of CO2 produced when burning a mature tree is less than the tree absorbed whilst growing. So if the tree comes from a managed forest, i.e. it is replaced once felled, then using such wood for fuel is ‘CO2 negative’.
Wood is a renewable energy source, a new tree takes around 20 years to mature to a sufficient size to be used for burning, whereas fossil fuels take millions of years to form. Burning wood releases less of the gases that damage our ozone layer (the layer of gas in the atmosphere that protects us from harmful levels of ultraviolet radiation emitted by the sun) than leaving it to rot naturally.
Wood has its flaws; there are many varieties and not all burn as well as each other, it produces smoke, soot, tar and Carbon Monoxide which are dirty and dangerous, it takes up a lot of room to store and whilst it is less polluting than coal, it doesn’t produce as much heat. Many people prefer the experience of burning wood over coal.
Burning Seasoned Wood
There are numerous types of wood used in the UK as firewood. Their suitability differs hugely so it is important to choose the right type and it is essential that wood is properly ‘seasoned’ before use.
Hardwooods burn longer than softwoods as they are more dense and therefore less wood is required. Softwoods contain more resins (sap) which produce more dangerous byproducts like creosote that can cause Chimney Fires.
All wood naturally contains a lot of moisture and it can soak up more moisture if not stored properly. Moisture content differs by wood type but all ‘green’ wood (freshly cut wood) contains levels of moisture that are too high for burning. Burning green wood or wood that has not been seasoned enough and still has a high moisture content is wasteful, as some of the fuel energy is used up evaporating the moisture which reduces the energy released as heat. The moisture that evaporates can itself cause serious problems as it condenses inside the chimney flue causing more creosote to build up in the flue.
Moisture in wood is measured as a % of the overall weight of the wood. Seasoning wood is the process of chopping and splitting it into logs and storing it under cover from rain but with an open air supply to allow the wood to dry out. Ash has one of the lowest moisture contents when green at around 35%, i.e. 35% of the weight of a piece of Ash is moisture. Oak has a moisture content of around 50% and Spruce has a moisture content of over 65%.
Wood left to season naturally will end up with a moisture content of around 18 – 20%. It is unlikely to drop lower than this due to the natural level of humidity in the air. Wood with a 20% moisture content is safe to burn. Kiln dried wood has a moisture content of around 10%. Ash can season from 35% to 20% in around 6 months (under the right conditions) whereas oak can take two years or more to drop to 20%.
We have listed some of the commonly available types of wood found in the UK in the section below called ‘Common Types of Wood’. This is based on information that we have collected from various sources over time, it is not a comprehensive list, they may be more types of wood in use across the UK that we haven’t mentioned. The list is in alphabetical order as opposed to quality order and it includes comments regarding suitability for burning.
The only accurate way to measure how much moisture there is in a piece of wood is to use a moisture meter. Old wives tales like ‘knocking two pieces of wood together and if it sounds hollow its fine….’ are clearly not very scientific and not to be relied upon.
Never burn wood that has a coating, e.g. paint or varnish, as they release toxic gases when burned. More on this is the section below called ‘Off-cuts, Floorboards & Wood from Skips’.
Common Types Of Wood
The list below shows some of the commonly available types of wood found in the UK. This is based on information that we have collected from various sources over time. It is not a comprehensive list, they may be more types of wood in use across the UK that we haven’t mentioned. The list is in alphabetical order as opposed to quality order and it includes comments regarding suitability for burning.
|Wood||Description As A Fuel||Quality As A Fuel|
|Alder||Low heat output, burns quickly||Poor|
|Ash||One of the best woods to burn, with a high heat output and steady burn rate. Can be burned 'green' (un-seasoned) but at it's best when seasoned.||Very Good|
|Beech||High heat output and steady burn rate, but only when seasoned.||Very Good|
|Birch||Fairly high heat output but fast burning. Can be burned 'green' (un-seasoned) but green Birch produces large amounts of sap which can add to sooty tar deposits in chimneys.||Good|
|Cedar||Fairly high heat output and steady burn rate, lasts well. Can spit and produce sap which can add to sooty tar deposits in chimneys.||Good|
|Cherry||Slow burning with a fairly high heat output. Must be well seasoned.||Good|
|Chestnut||Poor burning and low heat output.||Poor|
|Firs||Poor burning and low heat output. Produces sap which can add to sooty tar deposits in chimneys.||Poor|
|Elm||Slow burning and medium heat output. Requires cutting and splitting followed by a long period of seasoning to dry out properly, ideally 2 years.||Average|
|Hawthorn||High heat output and steady burn rate.||Very Good|
|Hazel||Good heat output but fast burning. Should be well seasoned, ideally a year.||Good|
|Hornbeam||Good heat output and slow burn rate.||Good|
|Horse Chestnut||High heat output and fairly slow burning. Spits a lot so better for stoves than ope fires.||Good|
|Oak||Fairly high heat output and very slow burning. Requires cutting and splitting followed by a long period of seasoning to dry out properly, ideally 2 years.||Good|
|Pine||Fairly high heat output but fast burning. Can produce large amounts of sap which can add to sooty tar deposits in chimneys. Requires cutting and splitting followed by a long period of seasoning to dry out properly, ideally 2 years.||Good|
|Poplar||Poor burning, low heat output and very smokey.||Poor|
|Spruce||Poor burning, low heat output.||Poor|
|Willow||Poor burning, low heat output.||Poor|
Off-cuts, Floorboards & Wood from Skips
It is very common to find nails and screws in ash pans and stoves when sweeping and it is one of the most common questions we are asked… ‘can I burn old floorboards? …. can I burn pallets? etc and many customers have mentioned collecting firewood from skips.
Burning wood with a high moisture content can be dangerous as mentioned in the section above called ‘Burning Seasoned Wood’. Wood in skips and pallets are very often kept uncovered outside and all wood can soak up water. Even thoroughly seasoned wood that is left out in the rain will start to soak up water meaning it is no longer suitable to burn until it has been dried out again.
Wood that has been treated with varnish, lacquer, any kind or paint or weatherproofing treatments are not suitable for burning. As well as creating noxious fumes, when it burns it releases corrosive chemicals that attack the inside of the flue. These emissions and moisture from the fuel form acids that can corrode bricks and lime mortar in brick flues which create a real risk of leaks, i.e. smoke escaping into other rooms in the property through cracks that form in the brick work. These acids can also attack steel flue liners that are installed with stoves, corroding holes in the liners that will again let smoke escape where it shouldn’t. This will invalidate guarantees given by the liner manufacturers (there are ways of testing corroded steel to prove what caused the corrosion).
The best wood to burn are hardwoods like Ash or Oak that have been chopped, split and seasoned thoroughly to reduce the moisture content down to 20% or less and stored under cover from rain but with a good air supply.
Coal has been used to provide heating in the UK for centuries. Open fireplaces not only provided direct heat, they also heated water in back boilers some of which fed radiators which provided much more heat than just the open fire. These coal powered radiators were the precursor to the modern radiators powered by gas and electric central heating systems.
The two most common varieties of natural coal still used in domestic heating systems are Bituminous coal (otherwise known as ‘ordinary house coal’) and Anthracite. Bituminous is a relatively soft coal of good quality (60 to 80% carbon content) and Anthracite is a much harder coal with very few impurities (92 to 98% carbon content) and is arguably the highest quality coal available.
Burning coal produces more heat than burning smokeless coal or wood and the better quality coal, the more heat. It does however produce more smoke and soot making it the dirtier. Sulpher emissions in smoke can mix with moisture in smoke to form acids that can attack the inside of chimney flues and flue liners, corroding brick, mortar and steel and potentially creating risk of leakage, i.e. smoke leaking into rooms rather than escaping out of the chimney. It can also burn very hot and cause damage to stoves, more on this in the section below called ‘Which Is Best In My Stove, Wood or Coal?’.
Smokeless Coal or Eco coal produces less soot and smoke than ordinary coal. There are many varieties and they are all man-made, i.e. they are manufactured using a combination of coal and renewable materials. Many smokeless coal suppliers claim that as well as producing less emissions, smokeless also produces more heat. In our experience and from listening to feedback from many customers who use smokeless coals, it produces less heat than ordinary coal and hardwoods and it often does not completely burn, i.e. there is a fair amount of un-burned coal left in the grate when the fire is out.
Which Is Best In My Stove, Wood or Coal?
First thing to make clear is, there are different types of coal which can be simply categorised as ‘smokeless’ coal and ordinary ‘house coal’. You must NEVER burn ordinary house coal in a stove. This fuel is way too hot for a stove and can cause serious and often un-repairable damage to the inside of a stove. Steel and iron can warp, bend and crack if it gets too hot. Ordinary house coal should be clearly labelled as such.
There is one major difference between a wood burning stove and a multi-fuel burning stove and that is stoves that are wood only do not have a grate as wood can be burned on a flat surface, i.e. the bottom of the stove. Multi-fuel burning stoves have a grate as coal MUST ONLY be burned on a grate and never on the flat bottom surface of a stove.
A grate is basically made of cast iron bars or a cast iron grid of some design which allows air to come up from below and ash to fall down into an ash pan. The grate is often movable, i.e. there is usually some mechanism built into the stove that allows you to move the grate from the outside to shake ash off it and through the gaps to the ash pan. This mechanism is often called a ‘riddling’ plate or riddling bars.
Coal can only be burned on a grate because whilst wood will burn happily sat on a pile of ash, coal requires air from both above and below to burn properly as well as an escape route for the ash. Ash can block the grate which will stop air getting to the coal. The grate can then overheat and warp or crack.
If you are burning wood you should only ever burn hard wood logs that have been properly seasoned. Never burn soft wood logs or unseasoned logs as they contain a lot more moisture and sap which can cause tarry deposits inside the flue liner which can lead to chimney fires. You should also never burn wood that has been treated in any way. The chemicals in the treatment can corrode the steel in flue liners and this will invalidate the liners warranty or guarantee. That’s why burning wood from skips is not a good idea. See the sections above for more info on this.
Generally we do not advise using coal in any stove, even if it is multi-fuel, for the following reasons:
Slow To Burn – When your stove is burning and your coal is reducing you will eventually need to top it up with more coal. When fresh coal is added to an already hot burning stove, the new coal can take some time to start burning properly. While it is getting going it releases large quantities of thick volatile yellowish-grey smoke, which fills up the chimney flue. When this smoke reaches a high enough temperature it can ignite causing an explosive flash which can cause damage to the inside of the stove including twisting / warping / cracking baffle plates and grates and damage to the flue liner, plus the possibility of smoke blowing back into the room through the air vents. If the stove is ‘slumbering’ i.e. not burning ferociously, perhaps because the air vents are closed, there is a greater risk of these explosive gases being produced, particularly if fresh coal has been added to the stove whilst its slumbering. This can also happen with wood when the stove is slumbering, but it is far less likely High temperatures – if the air supply into the stove is too high and there is a lot of coal inside, the temperature can become too hot for the stove to handle again potentially damaging baffle plates, grates and flue liners. More corrosive – wood releases moisture when it burns and coal gives off sulphur dioxide. If burned together these emissions can mix forming a weak sulphuric acid which can corrode the steel of the flue liner. For this reason multi-fuel stoves that will definitely be used to burn both types of fuel together require a flue liner made from a higher grade of steel to resist this corrosion, which is more expensive. Most people only use wood in stoves but often buy a multi-fuel stove as there little of no price difference between wood only and multi-fuel version of the same stove and its easy to keep clean thanks to the grate and the ash pan. Doing this you will only need a flue liner that is suitable for wood only.