A firewood kiln is an enclosed structure used to speed the drying process of firewood. The structure of the kiln is generally constructed in one of two ways: a permanent building or a mobile structure. Kiln buildings typically have a fixed foundation and are constructed expressly for drying firewood. The building is often well sealed and equipped with airtight kiln doors. The second kind of firewood kiln can be a more portable structure typically made from used shipping containers, which have been outfitted with special equipment used for kiln drying.
Features of the typical firewood kiln include a boiler or other heat source to generate warmth, fans for circulating warm air through the wood, and bins or racks used to dry the wood. Firewood kilns also usually have gauges to measure humidity and temperature. The kilns are often heavily insulated and then lined with waterproofed plywood. Some firewood kilns are equipped with tracks so wood can easily be moved into and from bins and racks.
Firewood kilns can be powered by various types of energy. Some kiln users choose to use natural gas while others use wood boilers. Some other fuel options include oil-fired boilers, electricity, and steam heat. Solar power can be used to augment other energy systems, but it generally does not generate enough power to efficiently run a firewood kiln on its own.
Without the use of a firewood kiln, seasoning firewood properly typically takes seven to twelve months. It is often difficult to keep seasoned wood dry, and there is no guarantee that it will remain free from pests and fungal growth. If wood is not kiln dried, it often cannot be sold commercially. In addition, seasoned firewood tends to create more creosote build up in woodstoves and chimneys than kiln dried firewood does.
Firewood kilns have many advantages. For example, they can ensure the humidity in the wood is at the optimal amount for the most efficient burn rate. Optimal wood moisture content is approximately 20 to 25 percent. Kiln dried firewood is also free from insects and fungi. This is important if the wood will be sold commercially. Kiln dried firewood also is cleaner looking, making it more desirable than traditionally seasoned firewood.
Since firewood kilns speed up the process of wood drying, the firewood producer who uses one will often benefit by being able to sell more wood that is of a higher quality than if he or she relied on seasoning. A good fixed foundation firewood kiln can dry up to 24 cords in two days time. A more portable unit can dry four to 13 cords in three to five days, depending on how it is constructed.