Abstract: A grain drying system around the interior of a grain bin wall which dries grain adjacent the bin wall while minimizing air and heat loss above the level of grain stored in a bin is disclosed. The system is self-regulating and limits air flow to areas above the level of the grain in response to changes in grain level or air pressure in the system. In the grain drying system, vertical air passageways or tubes extend about the interior of the bin wall. The elongated passageways, which have air diffusing or outlet areas, are arranged in fluid communication with a plenum chamber below an air permeable grain supporting subfloor in the grain bin. Each of the passageways or tubes has a movable float slidable therein. When pressure in the plenum chamber reaches a pressure equal to or greater than a predetermined level at which the floats are calculated to operate, the floats then rise within the air passageways until equilibrium with grain created air resistance is reached.