Abstract: A heat exchanger for use on existing grain dryers or integral to new grain dryers that recovers heat from the moist hot exhaust air leaving the grain columns and uses this recovered heat to preheat ambient air being drawn into the grain dryer via a blower. The heat exchanger utilizes heat exchange columns separated from ambient air columns by heat conductive walls. The heat conductive walls allow for a transfer of heat from the moist hot exhaust air through the heat conductive walls and into the ambient air being drawn into the grain dryer through the ambient air columns. The heat conductive walls do not allow for the mixing nor contact of the moist hot exhaust air with the ambient air. Therefore, heat is transferred to the ambient air being drawn into the grain dryer without the addition of moisture to the ambient air and the resulting decrease in moisture holding capacity that would result.