Types of Firewood
Green vs. Seasoned
Green Firewood has a moisture content greater than 50%. Any logs that have been cut down within 12 months should be considered green. A healthy standing tree will have a moisture content between 60% and 100+% (Yes, some trees can be more water than wood!). Thus green wood is any wood that has a moisture content of more than 50%, therefore making burning very ineffective because the potential BTU's (heat) of the wood will be lost in the release of the water through steam. The only true way to decrease the moisture content of wood is by opening the surface area of the wood to allow the water to evaporate via heat and air transfer. Firewood will not begin to fully season until split. You cannot completely season firewood in log or block form.
Signs of green firewood include: very tight end grain, uniform wood color, heavy wood, intact bark, mold/fungus, strong smell, sap, bugs or a dull "thud" when pieces are banged together end to end.
Seasoned Firewood has a moisture content less than 40% that will allow the wood to burn effectively and release the potential BTU's (heat). Wood that has been properly split and stored will promote the evaporation of water. In most areas of the country, especially the Northeast, it will take up to 12 months for split hardwood to be properly seasoned. Wood with more than 40% moisture content should not be burned for home heating. The minimum moisture content for optimal BTU's is no more than 20% to 30% moisture and as low as 10%. Below 10% the wood will burn too quickly.
Signs of properly seasoned firewood include: checks (cracks) in the ends, loss of wood color, lighter wood, loss of bark, no signs of mold/fungus, lack of smell and a loud "clang" when banged together end to end (like a baseball bat).
Kiln Dried vs. Air Dried
Kiln Dried Firewood is dried in a heated chamber removing water at very high temparatures. These specially designed kilns have been adapted from lumber drying kilns to specifically dry firewood in very short periods of time. Firewood kilns have a minimum temperature of 160 degrees with some reaching over 200 degrees. Kilns can dry firewood to below 20% moisture content in 48 to 72 hours.
The advantages of kiln dried firewood include: the wood has a consistently low moisture content, the wood is bug free, it is very clean, it can be dried very quickly and produced throughout the year, the wood produces the highest BTU's of any firewood, it burns clean and complete with no Creosote and very little ash.
Air Dried Firewood is seasoned outdoors using the sun and wind to evaporate water. Firewood that is air dried will vary in moisture content and drying time due to many different environemental factors.
The benefits of air dried firewood include: it is the cheapest drying method, large volumes can be dried at one time, the wood does not have to be moved from where it is processed, buyers can purchase wood from the drying area and it is less labor intensive than other drying methods.
Hardwoods vs. Softwoods
Hardwoods are very dense and they have more BTU's (= heat) per volume as compared to softwoods. They tend to be more difficult to start but will burn longer and release a good amount of heat. For all pratical purposes hardwoods are the best choice for firewood. Some hardwoods are better to burn than others. On Long Island we mainly burn Oak and Maple. They are excellent hardwoods for burning (as long as they're seasoned properly). Other quality burning hardwoods include: Ash, Beech, Birch and Hickory. There are other quality hardwoods but they are impractical to obtain in volume for firewood. Although most hardwoods do burn well there are a few that do not: Elm, Popular & Sycamore are among a few hardwoods that have poor burning characteristics.
Softwoods are less dense than hardwoods and tend to burn very quickly. They are good for starting a fire but will release a low amount of BTU's (= heat) per volume. Due to the high amount of sap in softwoods they are not recommended as indoor firewood. They may build up dangerous amount of Creosote in your chimney. If you do burn softwoods as firewood the following are the best choices: Doug Fir, Yellow Pine and Spruce. Most softwoods are best used as kindling and Cedar is among the best for that purpose. Cypress is among the worst softwood for firewood.