This heat is beneficial when conditioning, as the heat partially relieves stresses by plasticizing the wood. The heat also encourages moisture movement into the lumber, avoiding the risk of reverse case-hardening. That is, the dry-bulb temperature may be much above the set point, and the EMC achieved will be much lower than desired. For example, assume that the equalizing dry-bulb temperature is 170 F, with a 135 F wetbulb temperature. Turn off heating coils by using a low dry-bulb temperature setting on the controller or by manually closing the heating valve.
Thicker lumber requires slightly longer conditioning times.
After equalizing, cool the lumber for several hours. Leave the kiln doors and vents open with the fans running and the heating and humidifying systems turned off. Then, close the doors and spray steam into the kiln without heat. As the lumber's surface will be quite cool, the moisture from the steam will condense on the lumber's surface, providing rapid stress relief. Conditioning times may be as short as two hours.