Shopping for good quality firewood can be confusing - what's moisture content and why do you pay a premium for kiln-dried logs? When you get into the detail, seasoned logs are a false economy - but they're also worse for the planet than kiln-dried.
Why? Time for a science lesson!
Wood is hygroscopic, meaning it gains and loses moisture to the air naturally. When logs are cut, they will contain a lot of water, sometimes more than 60% moisture content, whereas the ideal for burning is 10% - 20%. The wetter the wood, the lower the temperature that it burns at and the higher the emissions of pollutants.
The moisture therefore needs to be removed before the logs can be used as firewood. There are two ways to do this - seasoning or kiln-drying.
Seasoned logs are dried naturally over a period of time.
Depending on the species of wood and the conditions in which they're kept in, seasoned logs can take anywhere from 6 months to 2 years to properly dry. They need to be kept in a place with low humidity, off the floor, away from walls and obviously, out of the rain!
Because there are so many factors that affect how dry the logs will get, there is a massive variation in the quality and moisture content you get when you buy seasoned logs.
When we first started buying logs, we tried seasoned logs from a few different suppliers and found that the moisture content varied wildly, with some at the ideal 20% and some at a massive 40%!
Kiln-drying means drying the logs in a chamber, or kiln, where the temperature, air circulation and humidity are controlled. This means that the logs can be dried faster, to a more specific moisture content, which is usually below 20%. Whilst kiln-dried logs are often more expensive than seasoned logs, they will burn hotter, last longer and emit less smoke and ash. And who likes cleaning layers of thick soot from their log burner?
To reduce pollutants emitted from firewood, the government's Clean Air Strategy aims to tackle the burning of wood with moisture content higher than 20%, so it looks like kiln drying may even be made mandatory from Feb 2021. You can read more on that here.
We exclusively use kiln-dried for our logs, pizza logs and kindling, and we buy only from Woodsure "Ready to Burn" certified suppliers, so we guarantee less than 20% moisture content in all of our British firewood. Check out our firewood products here.