Timber & Wood Products
The most important property of good firewood is moisture content. Firewood should be fully seasoned (to below 20 percent moisture content) before being burned. Because it can be difficult to ensure that purchased firewood is properly seasoned, the best approach is to buy and stack firewood well before it is needed. There is no danger in over-seasoning wood – drier is better.
"W179 Wood Products Information - Moisture Content of 'Seasoned' Firewood," The University of Tennessee Agricultural Extension Service, W179 08-0079, http://trace.tennessee.edu/utk_agexfores/101