Green (unseasoned) Timber
This is the term used for freshly felled timber. The natural moisture content will be too high to burn efficiently, if at all.
For burning, firewood should be dried, or “seasoned,” until its moisture content is around 20 percent. Firewood with a moisture content higher than that may eventually burn, but it is extremely hard to light and just as hard to keep burning. Also, new high-efficiency wood-burning stoves will perform badly as much of the heat produced is wasted in turning the excess moisture in the wood to steam before the wood can be burnt.
Just as important, the stove will not reach high enough temperatures, to burn off the tars and creosote in the smoke produced by the fire. They will end up lining the inside of your flue pipes and chimney. They will also blacken the glass window of your stove and produce excessive smoke.
It is argued that you can burn Ash timber when it is ‘Green’ which is true, it will ‘burn’ because even when green it only has a moisture content of around 34%However it will produce much more of the all important heat if it contains less moisture, which, after all, is the objective.
To further demonstrate how important it is that the wood is dry:
A ton of wood with 50% moisture content has a calorific value (CV) of around 2,300 kWh but a ton of wood at 20% has a CV of over 4,100 kWh. That’s nearly twice as much heat warming your house.
In money terms, if a kWh of heat is worth 5p then a ton of wood at 50% MC is worth £ 116.38 but a ton of wood at 20% MC is worth £206.55. The higher value takes a bit of time and effort to achieve but the rewards are clear. (figures from forestry.gov.uk)
Some firewood suppliers will cut and split wood from a freshly felled tree and deliver the same day. This is ok if you are planning on storing the wood for at least a year to season but will not be suitable to burn immediately.
Likewise if the wood has been seasoned but has been stored out in the rain it could take weeks to dry out before it will burn efficiently. If you have no access to a moisture meter, good sign to look out for is cracks in the end grain of the logs like this:
Hardwood or Softwood?
Hardwood is the term used for Deciduous trees for example, Ash, Beech, Birch, Cherry and Oak. Hardwood tends to burn for longer so you will be loading the fire less frequently. It also produces longer lasting embers. If you have a large enough stove to take a very large piece of hardwood it can be left to burn for many hours once the stove temperature is hot enough.
Softwood is the term used for Evergreen trees such as Fir, Larch, Leylandiia and Pine. It tends to light more easily than hardwood and burns faster due to it being less dense and its resin content. It gives more immediate heat so is ideal for kindling and initial burning but produces very little in the way of long lasting embers and it is more likely to spit because of the resins present. For millions of North Americans and Scandinavians softwood is the only firewood available as Hardwood trees do not grow well in colder climates.
Typically, the heat content of softwood is little more than half as much as hardwood by volume. However by weight it is much the same. A ton of Hardwood will produce a very similar amount of heat to a ton of Softwood, but because it is lighter will take up more room for storage.
Kiln Dried or Naturally Seasoned?
Ok, so we have established that the wood needs to be good and dry, ideally under 20% moisture content. Kiln dried timber will certainly give you this, if it has been stored correctly and not allowed to get wet in the rain. However, a large majority of people burning wood to heat their homes, do so at least in part because of the environmental benefits in burning a renewable fuel over a fossil fuel. If the wood they are burning has been effectively cooked in an oven fired by oil coal or gas the environmental benefits are surely out weighed. Another consideration is where the timber has travelled from; there are many reputable companies within the UK selling kiln dried firewood. However if it has travelled great distances by road or hundreds of miles by sea from abroad, this again out weighs any environmental benefit. I did notice recently on the internet one company proudly advertising Hardwood logs from South Africa!
It is possible to achieve the low moisture content which is necessary for good firewood using natural, fuel free methods, it just takes a little more time and effort and we are very happy to put in the time and effort needed.
Storing your logs and kindling
It is very important to keep your logs and kindling as dry as possible, either in a well ventilated, shed, garage or log store. If you need a good quality log store we recommend Chesham Fencing Supplies based up in Wendover woods. Their stores come ready constructed and easily hold a truck load of our logs and a couple of sacks of kindling.
It is always a good idea if possible to get your logs and kindling indoors before they are needed as the warmer and dryer they are the better.
Lighting your fire
A fire can be lit simply by using lightly crunched up news paper with finely chopped kindling wood on top, but this can take experience and occasionally a few attempts.
The easiest and most failsafe way to get your fire going quickly is to place a firelighter in the center of the grate and light it. After a few seconds once it is burning well, place a large handful of our kindling wood on top of the burning lighter, one piece at a time, in a criss-cross fashion. Then add several smaller logs on top. Once they are burning well larger, heavier logs can be added.
If the kindling and logs are dry this will work every time.