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Dry kiln operator's manual

Informally Refereed
Authors: William T. Simpson
Year: 1991
Type: Miscellaneous Publication
Station: Forest Products Laboratory
Source: Agriculture handbook (United States. Dept. of Agriculture) ; no. 188. Madison, Wis. : U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory, 1991: vi, 274 Pages


The modern dry kiln is a unique product of research, development, and experience. It is the only practical means now in wide use for rapid, high- volume drying of lumber to conditions necessary for maximum serviceability in housing, furniture, millwork, and many other wood products. As part of our charge to help further the efficient utilization of our nation’s timber resource, Forest Service research and development in lumber drying has made a significant contribution to the technology. The Forest Products Laboratory (FPL) has been conducting research in lumber drying since it was established in 1910. Early work by Harry Tiemann (The Kiln Drying of Lumber: A Practical and Theoretical Treatise, J.B. Lippincott Company, Philadelphia, PA, 1917) at FPL established lumber kiln-drying technology and the first lumber dry kiln design. Tiemann’s book can really he considered the first drying manual. Several other FPL drying manuals followed before the 1961 manual by Rasmussen. A well- designed and properly operated dry kiln can in a few days or weeks turn green lumber fresh from the forest into a dry, stable material necessary for successful industrial enterprises in today’s highly competitive markets. The more critical the drying requirements, the more firmly the dry kiln becomes established as an integral part of the lumber mill, the furniture factory, or the millwork plant. For many wood products, kiln dried lumber is essential. Dried lumber has many advantages over green lumber for producers and consumers alike. Removal of excess water reduces weight and thus shipping and handling costs. Proper drying confines shrinking and swelling of wood in use to manageable amounts under all but extreme conditions of relative humidity. Properly dried lumber can be cut to precise dimensions and machined more easily and efficiently; wood parts can he more securely fitted and fastened together with nails, screws, bolts, and adhesives; warping, splitting, checking, and other harmful effects of uncontrolled drying are largely eliminated; paint, varnish, and other finishes are more effectively applied and maintained; and decay hazards are eliminated if the wood is subsequently treated or protected from excessive moisture regain. Efficient kiln drying of lumber is therefore of key importance in the utilization of our forest resource. On one hand, it helps to assure continued markets for wood products by increasing their service life, improving their performance, and contributing to consumer satisfaction. On the other hand, it helps to conserve our forest resource by reducing waste in manufacture and extending service life and usefulness of products. Both are essential in using timber wisely, which has long been an accepted tenet of forest management policy. The full benefits of modern kiln-drying technology can be gained only when certain prerequisites are observed. Mill management must recognize the importance of efficient operation to quality of product, and operators must be well trained and encouraged to apply the best techniques. Quality should not be sacrificed for quantity in the production of kiln-dried lumber. The high value of our timber resource makes it uneconomical to do so.


Kilns, Kiln schedules, wood properties, drying, wood handling, handbooks, drying defects, kiln drying, seasoning (wood)


Simpson, William T. 1991. Dry kiln operator''s manual. Agriculture handbook (United States. Dept. of Agriculture) ; no. 188. Madison, Wis. : U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory, 1991: vi, 274 Pages