A grain drying and conditioning apparatus having a housing with an outer pervious skin with impervious end walls, air inlet, grain inlet, grain outlet and air exhaust duct structures connected thereto has air pervious walls which are spaced within the structure for confining a column of grain to be dried. A blower and heater mechanism is also connected to the housing for causing heated air to be forced through a first zone of the column of grain in one direction to heat and extract moisture therefrom and simultaneously causing air for cooling the grain to be pulled through a second zone of the grain column in an opposite direction, or, by simple adjustments, to be pushed in the same direction as the flow of the heated air. A plenum chamber is formed between the innermost of the pervious walls, the air duct structure, and a rear bulkhead wall opposite the air duct structure; an adjustable plenum divider mechanism is provided between the innermost of the pervious walls and the air duct structure in the plenum chamber for selectively dividing the plenum chamber into a first and a second section for the purpose of optimizing the heating and cooling of the grain in the first and second zones, or for combining both zones of the plenum chamber for optimum heated air drying in the entire structure.Air recycling structure and specific air control devices for regulating the volume of exhaust air versus recycled air in the exhaust areas of the dryer is provided for blending unsaturated exhaust heated air which was forced through the lower portion of the first zone (drying zone) of the grain column area by pressure with incoming cooling air drawn through the second zone (cooling zone) of the grain column area by suction to save the energy in such heated air.