A hopper bottom for supporting a cylindrical side wall of a grain bin includes a hopper wall having an inverted cone shape supported on upright support legs. A manifold duct is supported above the hopper wall to define a manifold passage therein extending circumferentially adjacent to the peripheral edge of the hopper wall. A plurality of outlet openings formed in the manifold duct in communication from the manifold passage to an interior of the hopper wall for open communication with the grain bin thereabove. An inlet opening extending through the hopper wall in alignment with the manifold duct receives ventilation air from a blower to direct the flow through the manifold duct and into the grain bin through the outlet openings of the manifold duct.