Green vs Seasoned Firewood?
When selecting firewood its important to be sure the wood you are collecting or buying is seasoned. "Green" or "Wet" generally refers to wood that has been freshly cut and has not had adequate time for internal resins or sap to dry. This drying prosses is called "seasoning" and the time required depends on a number of factors. Generally, the more surface area exposed to air, the faster the wood will reach a seasoned state.
Proper seasoning can take months or years. Open grain woods split into thin pieces can take as little as 6 months for the resins to dry, while thicker hardwood pieces can take 18 to 24 months. If a large log is simply cut to length and not split, the drying process can take much longer, even decades for certain species. Seasoned firewood will have been cut split and dried long enough to the internal moisture content to level off around 20%.
There is a difference between firewood that is wet and wet firewood. It does not have to be covered or protected from the elements. The most important element is airflow. With proper ventilation, firewood will dry and become seasoned with time. If it is exposed to rain, only the very outside layer is affected. While moisture on the outer layer of otherwise seasoned firewood can hinder the starting of a fire, it has little effect on an effect on an established fire. Firewood can be wet on the outer layer, but wet or green firewood refers to the internal moisture content.