Abstract: Heat treating firewood in basket using a kiln having a burner side placement area and an opposite side placement area for receiving baskets containing firewood. The two placement areas separated by a set of downcomers that provide heated air. Loading the kiln with baskets of firewood through the use of at least one of the first end wall and the second end wall. Applying a charge to heat the baskets of firewood. The application of the charge circulating heated air for the kiln from the mixing chamber and returning the heated air to the kiln through the supply duct till the dry bulb temperature reaches an initial target temperature above 230 degrees Fahrenheit. After reaching the initial target temperature for dry bulb temperature, increasing the wet bulb temperature depression target while working to maintain the dry bulb temperature within a selected tolerance with respect to the initial target temperature.

Abstract: A mixing chamber assembly for mixing burner output with kiln return air. A first vertical duct that receives kiln return air from the first return duct when the kiln is operated in a first mode and receives kiln return air from the second return duct when the kiln is operated in a second mode. A second vertical duct in fluid communication with the first vertical duct so that the kiln return air enters the first vertical duct, travels upward, and changes direction to then travel downward in the second vertical duct to pass downward into a dispersion chamber to provide downward movement of the kiln return air. The dispersion chamber having a hot duct discharge to convey burner output laterally above a delay table surface. The downward movement of the kiln return air colliding with the burner output to provide mixing of the kiln return air with the burner output.

Abstract: Kiln design that uses a series of at least two subsections with airflow in constant but alternating directions instead of using bi-directional fans that periodically reverse directions. The uninterrupted alternating air flow may be used in continuous drying kilns (CDK) with two sets of carriages carrying spaced stacks of lumber travel in opposite directions through a sequence of chambers. The uninterrupted alternating air flow may be used with a set of at least one pathway for carriages carrying lumber to be dried where all carriages move from a first end of the kiln to a second end of the kiln.