Tuesday 11 January 2011

How To Burn Wood Efficiently

Understanding the way in which wood is burnt will allow you to burn wood in a more environmentally friendly way, reduce the costly maintenance required for your chimney and get more heat out of the wood. There are 3 stages in the wood-burning process:

Evaporation - When you light a stove a lot
of energy will be needed at first to boil away any moisture trapped inside the wood. This takes a lot of energy to drive the water out of the wood and convert it into steam, producing an inefficient fire that is not burning cleanly. Also, much of the energy wasted in evaporating water is energy that could have heated the stove and started heating the room. This is a waste of all three elements; wood, money and effort. This water trapped in the wood has a nasty habit of putting out the fire, the best way to avoid this is to use seasoned wood, Properly stored and seasoned wood will help to minimise these problems.

So what is seasoning?
Essentially it is m
aking wood fit for burning – by reducing its water content – usually by leaving it for a period of time in the right conditions. All wood contains water. Freshly-cut "green" wood can be up to 45% water, while well-seasoned firewood generally has a 20–25% moisture content. Well seasoned firewood is easier to light, produces more heat, and burns cleaner.
Emissions - As the heat of the fire intensifies, waste-gases (smoke) are released from the wood. Unburned smoke is emitted into the air either as pollution, or condensed in the chimney causing creosote build-up. It takes time for the air in your chimney to heat up. When it is still cold you get an effect similar to the condensation of hot breath on a colder window or mirror. So when the by-products of combustion (smoke in the form of gases) exit the stove, and flow up into the relatively cooler chimney, condensation occurs.

The resulting residue that sticks to the inner walls of the chimney is called creosote. Creosote is formed by unburned, flammable particulates present in the smoke. It is black or brown in appearance. It can be crusty and flaky, tar-like, drippy and sticky or shiny and hardened. Quite often, all forms will occur in one chimney system.

If the wood you are using is water logged, or green, the fire will tend to smoulder and not warm the chimney sufficiently. Wet wood causes the whole system to be cool, and inefficient. In contrast: dry wood means a hot fire, which results in a hot flue, and a hot flue means much less creosote clogging up your chimney.

Charcoal - When most of the tar and gasses have burned the remaining substance is charcoal (ash in it’s finer form). A hot bed of charcoals and ash can enhance the combustion process when burning larger pieces of wood. Start with a small fire to develop a bed of glowing embers. As the charcoal bed develops and the cooker heats up, slowly add larger and larger pieces of wood. It takes time to build a good charcoal bed, but it is well worth the effort. Only empty excess ash periodically and always leave a bed of ash on which to light the next fire.

Every type of wood is different, some such as ash burn well and produce plenty of heat, in contrast Poplar, the same wood that is used to make matchsticks! burns very slowly and produces very little heat. Below is an interesting poem to help you remember which wood to use and which to avoid!
Logs to burn, logs to burn,
Logs to save the coal a turn
Here's a word to make you wise,

When you hear the woodman's cries.
Never heed his usual tale,
That he has good logs for sale,
But read these lines and really learn,
the proper kind of logs to burn.
OAK logs will warm you well,
If they're old and dry.
LARCH logs of pine wood smell,
But the sparks will fly.
BEECH logs for Christmas time,
YEW logs heat well.
SCOTCH logs it is a crime,

For anyone to sell.
BIRCH logs will burn too fast,
CHESTNUT scarce at all
HAWTHORN logs are good to last,
If you cut them in the fall
HOLLY logs will burn like wax
You should burn them green

ELM logs like smouldering flax
No flame to be seen

PEAR logs and APPLE logs,

they will scent your room.
CHERRY logs across the dogs,
Smell like flowers in bloom
But ASH logs, all smooth and grey,
burn them green or old;
Buy up all that come your way,
They're worth their weight in gold.

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