Abstract: A method and apparatus for drying stored grain based upon phenomena related to wet bulb temperature, depression, relative moisture, and relative humidity. The invention contemplates a conventional grain storage bin in which a suitable storage volume is defined beneath a lower, preferably perforated floor. A lower air plenum defined beneath the floor receives air which is circulated through the bin to dry the stored grain. When activated a relatively low capacity gas heater heats the circulating air which is forced by a conventional fan through an interconnecting vent interiorly of the bin plenum. Fuel for combustion preferably is limited by a modulating valve controlled by a temperature-sensing probe disposed within the plenum. Operation is initiated by a humidistat disposed exteriorly of the plenum, which initiates heating in response to ascertainment of a control reference humidity. For drying purposes the temperature of ambient air is raised by no more than the control depression.