US Patent 11460249 Multi-pass lumber kilns

Embodiments provide a multi-pass kiln with two or more chambers, an entrance and an exit at a proximal end of the kiln, and a reciprocal flow path extending through the kiln from the entrance to the exit. Lumber charges traveling along the reciprocal flow path may travel in a first direction along one side of the heated second chamber before traveling in a substantially opposite second direction along the opposite side of the second chamber. The distal end of the kiln may be substantially sealed, and a pressure differential between the distal end and the proximal end may draw moist heated air from the heated chamber toward the exit and entry to preheat and/or condition lumber charges traveling through the first chamber.