How Wood Burns
Evaporation – When you light a stove a lot of energy will be needed at first to boil away any moisture which is left in the wood. Using energy to drive off excess water in firewood robs the stove of energy needed for an efficient and clean burn. Also, much of the energy wasted in evaporating water is energy that could have heated the stove. Simply this is a waste of wood money and effort if you do not have seasoned wood to start with.
The presence of moisture tents to keep putting out the fire and therfore making it burn very poorly, which tends to produce a lot of creosote and pollution. Properly stored and seasoned wood will help to minimise these problems.
Emissions – As the heat of the fire intensifies, waste gases (smoke) are released fro 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 the chimney to heat up. When it is still cold you get an effect similar to the condensation of a hot breath on a cold 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 particles present in the smoke. It is black or brown in appearance. It can be crusty and flakey, tar like, drippy and sticky or shinny 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 hot fire, which results in a hot chimney stack therefore allowing less build up of creosote in the 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 stove 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 good bed of ash in the stove to light the next fire from, remember wood burns best in its own ash and embers.