Green wood is wood that has been recently cut and therefore has not had an opportunity to "season" (dry) by evaporation of the internal moisture. Green wood is relatively high in moisture relative to seasoned wood, which has been dried through seasonal passage of time or forced wood drying (as in kilns). Green wood is considered to be 100% moisture content relative to air dried or seasoned wood which is considered to be 20%. Available BTU charts for wood fuels tend to use air dried as their reference, thus oven dried or 0% moisture content can reflect 103.4% BTU content, exceeding the mean value. When green wood is used as fuel in appliances, it releases less heat per unit of measure (usually cords or tons) because of the heat consumed to evaporate the moisture. The lower temperatures that result can lead to more creosote being created which is later deposited in exhaust flues. These deposits can later be ignited when sufficient heat and oxygen are present to cause a chimney fire which can be destructive and dangerous.
'Green lumber' presents its own characteristics as well. Some species of wood are better used green because wood splits less when nailed green. Others tend to shrink excessively leaving voids between the individual pieces when allowed to dry. Often wood to be used for fine products such as furniture is 'kiln dried' to stabilize it and reduce the shrinkage/expansion of the finished product.
- NH Forest Market Report 1988, page 22