Properly seasoned firewood still contains a good amount of water, say 15 to 20 percent of its weight. This water regulates the combustion process along with a few other factors, such as the size of the part, the configuration of the load and the supply of combustion air. Around 30%, wood sizzles and fires are very slow and it is difficult to achieve clean burning until the wood is almost at the point of carbonization. You can reduce the moisture content of wood by seasoning, but seasoning can be a very lengthy process that allows the wood to dry for several months or even years.
Seasoning is the process of allowing wood to dry for an extended period of time to allow the climate to naturally reduce the moisture content of the wood to levels acceptable for use as firewood. Seasoning is a long process that can last between 6 months and two years, depending on factors such as the type of wood, the initial moisture content of the wood and the exposure of the wood to the elements. Keeping the wood open to the air, especially to the wind, will help the wood stay dry and low in moisture. If the moisture content of the wood starts to increase instead of staying at the same level or decreasing, it's a sign that the wood is starting to decay.
The EPA test method requires wood with a moisture content between 16 and 20 percent (19 to 25% on a dry basis) and, when the wood is outside this humidity band, the emission rate of the stove increases. The higher the humidity of the fuel, the slower the wood decomposes when heated due to all the thermal energy absorbed by boiling the water in the wood and raising the temperature of the steam. The CSIA states that it can keep the wood stored for up to 3 or 4 years without any problem of the wood being damaged if you follow these recommended procedures for storing wood. In doing so, the wood can start to decay and rot because moisture is trapped under the cover and because the wood is not properly exposed to the sun and wind.