Abstract: A drying kiln for lumber. The kiln comprises a drying chamber having two spaced drying sections each to receive a stack of lumber. There is a second chamber above the drying chamber and drivable, reversible, circulating means in the second chamber. The kiln also has heating means for air circulated by the circulating means. A first passageway permits the circulating means to force heated air across the drying sections, across the space between them and back to the circulating means. A second passageway extends downwardly into the space between the dryer section. There is a first and a second closable inlet for the second passageway. Each inlet is positioned on a side of the circulating means to receive a proportion of air forced towards it by the circulating means. A plurality of outlets to said space are in said second passageway. Means control the first and second inlets whereby if one is open the other is closed.