Living trees and fresh logs contain a large amount of water, between 40 and 65% depending on the species of tree.
It is very inefficient to burn fresh or wet logs because much of the heat produced as the log burns will be required to drive off the moisture contained within the logs as steam.
Kiln dried logs have a moisture level of below 20% and in some cases as low as 15%. You would need to burn around three times as many fresh logs to achieve the same heat output.
Burning fresh logs can also cause serious problems with your chimney or wood burning flume. Water vapour will combine with other gases and particles and the condensation forms a creosote-like substance which hardens to form tar on all surfaces. The chimney or flume can become blocked or the volatile residue can catch light, causing a chimney fire.
Excessive condensation can corrode any metal surfaces and can lead to perforation.
Kiln dried wood is timber that has been dried in a kiln oven. This is a quick and efficient process to produce logs that are ready to use.
Kiln dried wood is the most popular type of log. This because they produce a clean burn, a high heat and are ready to use as fire place logs straight away.