Abstract: An oven for electronics manufacturing including a heated chamber having openings at each end to the ambient environment wherein heated air is circulated by a centrally located fan to pass over workpieces in a substantially upward (or downward) flow. Equal temperatures at the entrance and exit ends of the heated chamber are promoted by a crossover air return arrangement in which a portion of the air from each end of the heated chamber is mixed with the air from the other end of the chamber as the circulating air is drawn into the fan for recirculation. In addition, a moveable shutter mechanism is provided at the entrance end and exit end of the heated chamber to adjust the air flow at the ends of the heated chamber. The shutter mechanism operates to selectively close off an adjustable portion of the heated air flow at the ends of the heated chamber.