A numerical study is made of buoyant flow and heat transfer in a vertically mounted cup-like cylinder which rotates steadily about the longitudinal axis. The temperature at the cylinder sidewall is lower than that of the surroundings. The relevant nondimensional parameters are identified. The governing Navier-Stokes equations, with the Boussinesq-fluid approximation, are solved numerically. The rotational Reynolds number Re is large, and the cylinder aspect ratio is O(1). The three-component velocity and temperature fields are portrayed. When the base surface is insulated, for the Richardson number Ri greater than or equal to O(1), the meridional flow weakens, the boundary layer-like character in the temperature field diminishes, and the azimuthal flow approaches that of a rigid-body rotation. When the base surface is transferring, the velocity fields are little altered from those of the insulated base, but appreciable differences are seen in the temperature fields. Physical explanations and rationalizations are offered on the basis of numerical results. Detailed profiles of local Nusselt numbers at the solid boundaries are provided. The trends are consistent with the physical reasonings. (C) 2000 Elsevier Science Ltd. All rights reserved.