A Guide To Burning Wood
Soft or Hardwood?
Traditionally hardwoods - Oak, Sycamore, Ash - have been considered better as fuel than softwoods - Larch, Spruce, Douglas Fir. The reason is that hardwood is denser, so an identical sized hardwood log actually contains more carbon, provides more heat and burns longer.
The truth is both are good fuels. A kilogram of softwood can have the same calorific value as a kilogram of hardwood. You will need a greater volume of softwood logs to get the same energy, because they have a lower density, but they are generally cheaper. If you have room to store more logs and you don’t mind re-filling your stove a little more often then softwood could be for you.
Wet or Dry?
The most important measure for wood fuel quality is moisture content.
Burning wet wood with more than 25% moisture content creates corrosive smoke and tar that can damage flue linings and cause chimney fires - it is not GREEN! Dry wood produces little smoke, low tar deposits, and high efficiency heat output, especially when burnt in a modern appliance able to efficiently burn combustion gases.
Wood for Burning - Seasoning
One of the most common mistakes people make is to burn green, non-seasoned wood. Green wood can contain up to 75% moisture, a figure that has a considerable effect on the calorific value of the wood, since part of the heat released is used to evaporate the water content and is then dispersed into the flue along with the water vapour produced.
Wood for burning in a wood stove must first be seasoned for a period of about 18-24 months, so as to reduce its moisture content to 15-20%. This clearly increases the price of the wood due to storage prior to sale but without such seasoning a significantly greater amount of timber will need to be burnt to get a similar heat output as seasoned wood.