What is the best fuel for a wood burner stove?
First determine if you have a wood or multi-fuel stove. Does it have a grate?
Wood burns best on a flat bed of ash. Coal needs to be on a raised grate to allow extra air flow underneath to enable the efficient combustion at a higher temperature.
Stoves are designed specifically for either wood or multi-fuel. Some wood burners do have conversion kits for multi-fuel use but check your liner is suitable. A survey by the Stove Industry Alliance found 77% of multi-fuel stove owners use their stoves exclusively for burning wood.
There are two grades of stainless steel used in twin walled flue liners, 316 and 904 (higher grade). You have 3 options: 316 both layers, 316 outer and 904 inner or 904 both layers.
The most common and cheaper installation is 316. Check your HETAS installer invoice or the data plate to check which you have.
316 are not suitable for any type of coal, only wood. 904 are suitable for either wood or smokeless coal. Smokeless coal increases flue deposits and acidic corrosion
Never use house coal in a stove, it burns far too hot. Coal produces much more CO2 so is also less environmentally friendly.
Golden Rule 1: Even if you have a multi-fuel stove do not burn wood and coal together. When burned together the sulphur released by the coal and water moisture from the wood combine to create a nasty corrosive solution that sticks to surfaces in the system. Especially vulnerable is the liner.
How to get the best from your wood burner:
Dry seasoned (2yrs) or kiln dried wood are best. Never any MDF, tantalised (treated garden timber), varnished or painted wood or other waste material. Treated wood release carcinogens and other toxins as well as particulate matter into the air.
Dry wood means less than 25% moisture content. Trees are normally felled in the winter, for the domestic market, when their moisture content is at its lowest. In the summer the water content can be up to 65% of the weight of newly felled timber.
Energy is wasted burning off water and it increases the build up of creosote in the flue. You burn about 3 times the amount of unseasoned wood to achieve the same heat output of seasoned wood.
Accurate checks can only be done by splitting a log and using a moisture meter. Usually the bark on seasoned logs comes away easily. Looking at the end of a log, radial cracks deep enough to be described as splits should be evident. Tap a seasoned log on a hard surface and it should have a hollow sound, rather than a dull thud sound from a damp log. The colour of seasoned wood fades over time, markedly different to that of green wood.
You can dry out your own wood in a wood store if you have the facilities; otherwise ensure you buy seasoned wood from your supplier.
Which is best, hardwood or softwood?
Softwood has the same heat content, or calorific value, by weight as hardwood. Hardwood is much denser, so has a higher calorific value by volume, typically almost twice that of softwood. Cost wise hardwood is more economical than softwood. Softwood tends to light more easily than hardwood and burns faster due to its resin content, so ideal for kindling and initial burning. Softwood seasons much faster than hardwood. Hardwood tends to produce less smoke than softwood.
It is generally recommended best to burn a combination of both types. Getting the wood burner up to its efficient operating temperature is best achieved initially using just softwood then introduce the hardwood logs later.
Hardwoods: broad-leafed, deciduous trees that lose their leaves in winter, such as Oak, Ash, Beech, Birch, Sycamore and Elm.
Softwoods: coniferous trees which are evergreen, have needles and cones, such as Cedar, Scots pine, Douglas fir, Larch, and Spruce.
Guide to common types of wood logs
Low heat and burns quickly.
Burns slowly, small flame, pleasant scent, no spitting/sparking.
Low smoke, excellent flame, good heat output, burns at steady rate, low moisture content, but 30% lower calorific value by volume than oak.
High water content, 2yrs to season, burns well.
Fast burning, good heat output, best mixed with slower logs: Elm, Ash or Oak.
Burns well, longer lasting heat, pleasant smell.
Slow burning, good heat output, 2yrs to season, pleasant smell, no spitting.
Reasonable flame & heat output, good smell.
Burns well, plentiful supply due to Dutch Elm Disease, slow burning lasting heat.
High water content, long seasoning time, pleasant aromatic smell, burns fast.
Steady burning, good heat output, thorny, difficult to handle.
Excellent firewood, allow to season, burns fast, bright flame, no spitting.
Low heat output, burns fast, bright flame.
Low quality firewood.
Must be well seasoned, reasonable heat, leaves oily sticky deposits in the flue system.
One of the best firewood. 2yrs to season, high calorific heat output, lasting heat even from just embers, burns slowly.
Burns slow and steady, reasonable heat, pleasant smell, poor flame, no spitting.
Fast burning, common kiln dried joiner’s wood, bright flame, high in resin, spits, oily/sticky deposits in flue system, good kindling.
Not recommended, burns poorly with unpleasant black smoke.
Burns quickly, low heat output, smokes and sparks, low quality firewood.
Burns well, moderate heat output, good flame.
Slow burning, tremendous heat output.