Abstract: A grain dryer has pair of heating columns in communication with an upper plenum, and a pair of cooling columns in communication with a lower plenum. A heater is located between the lower plenum and the upper plenum, wherein air is heated by the heater as air in the lower plenum is pulled through the heater and into the upper plenum. As the grain flows into the cooling column, it is exposed to cooling air being pulled through the cooling column into the lower plenum. A cooling air bypass system having a plurality of bypass tubes brings bypass air into the lower plenum from outside the grain dryer without having the bypass air come into contact with the grain being cooled in the cooling section. The cooling air bypass system includes a grill with an adjustable damper to adjust the amount of bypass air that flows into the lower plenum.