Abstract: A double pass reversing dryer provided with a main heat source for heating air passing through the upper plenum and a supplemental heat source for heating air as it passes from the upper plenum to the drying bin. When the double pass reversing dryer of the present invention is in an unbalanced state with more high moisture content agricultural material to be dried than low moisture content agricultural material to be dried, the temperature in the upper plenum is reduced and some of the air is vented directly to the lower plenum. The remainder of the air in the upper plenum is heated by a secondary heat source before the air passes into the drying bin containing the low moisture content agricultural material.