A Nusselt number, appropriate for forced convection in a channel bounded by two parallel plate walls heated asymmetrically, is introduced and evaluated for various velocity profiles, for either uniform heat flux or uniform temperature boundary conditions. It is shown that the value of this new Nusselt number is independent of the asymmetry if and only if the velocity profile is symmetric with respect to the midline of the channel. (C) 2004 Elsevier Ltd. All rights reserved.