When running a wood fired heating system it is important to understand your fuel. There is very little calorific difference of wood types based on their dry weight. Woods with a greater density burn for a longer time, as it has a higher calorific density. The most important (part/ aspect) of burning wood is to make sure it is dry.
Moisture content in wood
When a tree is felled in winter, the moisture content of the wood will be over 50%, and even higher if it is felled in summer. By splitting the logs and/or cutting them to short lengths, you can accelerate the rate at which the wood will dry out. You can check how dry it is using a moisture meter.
The reason the wood needs to have dried out is that when you put a log into a fire or stove, before it can burn, all of the moisture must be driven off, and this uses some of the heat from the fire – so, the wetter the log, the less heat you get out. But there’s another problem too – wet wood doesn’t burn as cleanly, which is bad from the point of view of pollution, and also can deposit tar in the chimney, potentially creating a fire risk.
So how dry should your wood be before you burn it? This varies from one stove to another, but the moisture content should be 30% at most, and ideally should be 20%. How long it takes to get this dry depends on how the wood is stored. Ideally it should be split as soon as possible, then stored off the ground in a place where air can circulate through it and the rain is kept off it. Drying to 30% should usually happen within a year, and 20% in two years, although in ideal conditions these times can be reduced.
Types of firewood.
Alder: Opinion varies, works best well seasoned.
Apple: Splendid/ It burns slowly and steadily when dry, with little flame, but good heat. Good scent. Must season well
Ash: Best burning wood; has both flame and heat, and will burn when green, as it has a low moisture content. Will burn even better dry.
Beech: Best when well seasoned
Birch: The heat is good but it burns quickly with a bright flame. Nice smell, works well when mixed with other woods that burn more slowly.
Cedar: Good when dry. It gives little flame but much heat, and the scent is beautiful.
Cherry: Burns slowly, with good heat. Another wood with the advantage of scent and does not spit.
Chestnut: Mediocre. Apt to shoot embers. Small flame and heating power.
Cypress: Burns well but fast when seasoned, and may spit
Douglas Fir: Poor. Little flame or heat.
Elder: Mediocre. Very smoky. Quick burner, with not much heat.
Elm: To burn well it needs to be kept for two years. Even then it will smoke.Very high water content – more water than wood.
Hawthorne: burns well
Hazel: Good, burns fast without spitting. but has other uses, so you might not want to burn it
Holly: Good, will burn when green, but best when kept a season.
Hornbeam: Good, burns well
Horse Chestnut: Good flame and heating power but spits a lot.
Laburnum: Totally poisonous tree, acrid smoke, taints food and best never used.
Larch: Crackles and spits, scented, and fairly good for heat. Oily soot in chimneys
Laurel: Has brilliant flame.
Lime: Poor. Burns with dull flame.
Oak: Dry oak is excellent for heat, burning slowly and steadily with a good heat. Seasoned for 2 – 3 years is best.
Pear: Slow and steady, good heat and a good scent.
Pine: Burns with a splendid flame, but apt to spit. Needs to be well seasoned. Gives off a large number of resins.
Plane: Burns pleasantly, but is apt to throw sparks if very dry.
Plum: Good heat and scent.
Poplar: Burns slowly with little heat – better for making matchsticks
Rhododendron: The thick old stems, being very tough, burn well.
Robinia (Acacia): Burns slowly, with good heat, but with acrid smoke.
Rowan: Burns well
Spruce: Burns too quickly and with too many sparks.
Sweet chestnut: burns well when seasoned but sends out sparks. Only for use in a stove with door closed!
Sycamore: Burns with a good flame, with moderate heat. Useless green.
Walnut: Good, and so is the scent. Aromatic wood.
Willow: Poor. It must be dry to use, and then it burns slowly, with little flame. Apt to spark.
Yew: Last but among the best. Burns slowly, with fierce heat, and the scent is pleasant.
More information on preparing your firewood can be found here