Lumber needs to be dried before use to assure against warping, and a homemade wood kiln is an innovative way to dry your own lumber. According to Jamie Duckworth of Woodweb.com, it is even possible to build a solar wood kiln that not only is small and takes up very little space, but essentially uses nothing but the sun to dry out wood staves to a specific humidity level. Whether you choose to build a solar-, fire- or water-powered kiln, make sure it is sized appropriately to achieve the best results.
Kilns are operated by dryheating freshly cut wood slabs. One of the best ways to provide dry heat and low humidity is by utilizing heated water in a radiator-type kiln system. Essentially, water pipes are run throughout the kiln and warm water is passed through them while fans blow air throughout the kiln room. This heats the air and circulates the air, lowering the humidity. The water pipes have a constantly circulating supply of hot water going through them, heated by a constant heat supply. Build an appropriate-sized room with a single door and no windows. Suspend heating pipes throughout one side of the building or from the ceiling, and make sure that at least one side has a bank of fans. Load boards into the kiln and heat the water, circulating it through the pipes. Turn the fans on and monitor the drying process weekly. These kilns are best for large operations due to their efficiency and energy input.
Fire-powered kilns are built much the same way as water kilns, except the air in the kiln is heated not with water, but by the fire directly. Many kilns of this type utilize gas heaters or some other type of controlled flame to heat the inside of the kiln itself, again using fans to circulate air throughout the kiln. Fire kilns are best for smaller or medium-sized operations and simply require a flame-powered heater to be situated at one end of the kiln with a fan blowing the warm air throughout the kiln itself. Again, drying should be monitored weekly. Be extremely careful not to provide any chance for the open flame to contact the wood.
An effective kiln can be made utilizing the power of the sun as long as the kiln itself is quite small and is situated facing the rays of the sun on a nearly constant basis. Solar kilns rely on the convection of the sun's rays to heat the inside of the kiln, yet still utilize fans to draw moisture out of the air. Build a small shed and fill it with shelving for the wood, making sure there is plenty of space between each board. Install fans along one side of the building, and build a slanted, glass roof. Face the building toward the south, and place it out in the middle of an open field so it catches the most sunlight. Place the boards on the shelving and keep the doors to the building closed all the time. Use the fans to draw moisture out of the kiln air, and check the moisture of the boards weekly.