Firewood: Hardwood verses Softwood

By The Helpful Engineer / On / In Energy Conservation

Hardwood v softwood
Hardwood v softwood

I try and burn hardwood in my stove where possible. But recently I received a load of mixed softwood instead. It was interesting to note how quickly it burned in the stove compared with hardwood. This meant much more tending of the fire.

The end result is that I will always try and obtain hardwood where possible from now on.

Comparing wood. Generally all timber contains the same amount of heat energy per kg of weight. Therefore the density of seasoned timber indicates its potential heat output. Below is a list of various common seasoned timber densities. The difference between hardwood and softwood is immediately apparent:

Hardwood

  • Oak is 750 kg/m3
  • Beech is 725 kg/m3
  • Ash is 700 kg/m3

Softwood

  • Pin is 600 kg/m3
  • Larch is 500 kg/m3
  • Douglas Fir is 500 kg/m3

The above figures assume seasoned timber (i.e. 15% moisture content). Fresh (green) timber will contain substantially more moisture, it would also be unsuitable for burning.

Hardwood is a more economic fuel. Based on the above figures, common softwood is approximately 30% less dense than common hardwoods and therefore produces 30% less energy. But my local timber supplier sells seasoned hardwood logs (mixed) for only 15% more than the mixed softwood. Therefore there really is no point buying seasoned softwood, if you have the choice. It costs more per unit of energy produced and it burns faster, produces less heat and needs more storage area.

But softwood does has some advantages for firewood; it drys (seasons) quicker than hardwood when cut. Which is an important consideration from an Irish perspective, with our mild and moist climate. It is also easier to light which means softwood is usually used for kindling.

Finally a  poem about the advantages and disadvantages of different types of firewood, which seems to agree with my recent experience;

The Firewood Poem (1930)

By Celia Congreve

Beechwood fires are bright and clear
If the logs are kept a year,
Chestnut’s only good they say,
If for logs ’tis laid away.
Make a fire of Elder tree,
Death within your house will be;
But ash new or ash old,
Is fit for a queen with crown of gold

Birch and fir logs burn too fast
Blaze up bright and do not last,
it is by the Irish said
Hawthorn bakes the sweetest bread.
Elm wood burns like churchyard mould,
E’en the very flames are cold
But ash green or ash brown
Is fit for a queen with golden crown

Poplar gives a bitter smoke,
Fills your eyes and makes you choke,
Apple wood will scent your room
Pear wood smells like flowers in bloom
Oaken logs, if dry and old
keep away the winter’s cold
But ash wet or ash dry
a king shall warm his slippers by.

 

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