Trees vary enormously in moisture content when felled. In summer, up to 65% of the weight of newly felled timber can be water.
Forestry work continues all year round but for the domestic heating market, trees need to be felled ideally in winter and certainly by the end of March when the moisture content is at its lowest. Trees felled in summer will take much longer to season. Some species of trees felled in winter will be ready for use the following winter. The target moisture content is 20% or less (wet basis) and this is often specified by the appliance manufacturer. Firewood ready for burning should never contain more than 25% moisture.