A guide to fire wood, for wood burning stoves and log gasification boilers

As a business we are constantly having the conversations about fire wood, we always amazed by the theory’s people come out with, for example yesterday I was at a potential customers home, who has a small ash plantation. He proceeded to explain that ash wood could be burnt wet, I asked him why ash had these magical properties. His answer was its true I read it online.

So who makes up the theories? Well frankly, who cares.

What’s important is that customers are burning fire wood with a maximum moisture content of 20 %. To test your fire wood take one of your logs that you think is ready to burn. Split the log down the grain and use your moisture meter to test the core of the log, if it has a moisture content of 20% or lower it is fit to burn. Note different woods with different densities will dry out at different rates, also a large chunk of wood will take longer to dry out than a smaller split piece of wood.

But why is it so important to burn dry wood ( max 20%). The moisture content in wood is simply water, when you burn the wood the water is converted to steam which makes its way up your chimney to the atmosphere, if you have a excess of water you will have a excess of steam which will cool the burning temperature in the fire box and lower the flue gas temperature.

1. A lower fire box temperature due to too much moisture ,this will mean less heat is produced to the room or to the boiler as you are simply drying the wood in the fire box instead of converting the wood to heat energy.
2. You will get dirty glass and tar build up within your appliance and chimney system, reducing its lifespan and efficiency
3. A greater chance of chimney fires, this is caused by tar build up within the chimney. Chimney fires reduce the lifespan of the chimney drastically
4. By having a lower fire box temperature, you burn off less emissions, creating more fly ash and more smoke. So that defra approved appliance suddenly is not as clean burning as it’s supposed to be .
5. Blocked chimney, causing potential carbon monoxide poisoning.
6. Poor heat output

Most woods have very similar energy value per kg , most people have issues understanding this as the pick up a log of beech and another of Sitka spruce both are the same size but the beech has a much greater mass and greater calorific value. This is because the beech is much denser.

However, 1 kg of beech is roughly the same energy value as 1 kg of stika spruce but not the same bulk.

Therefore, you may need twice the volume of soft wood compared to hard woods e.g. beech / oak, to create the same amount of energy.

Next time we will go through kiln dried wood opposed to air dried. What’s the difference?