Abstract: An aeration system for grain bins includes a plurality of outlet ducts extending radially outwardly from a central manifold when the grain bin has a flat floor; and a plurality of outlet ducts extending radially upwardly and outwardly from the bottom center of the bin when the floor of the bin is conical. Each outlet duct is defined by a pair of elongated, contiguous side walls which define a triangle with the floor of the bin; and a plurality of louver-type openings in such side walls for discharging air into the contents of the bin. Centrifugal or other fans are used to supply air to the manifold and outlet ducts.