In this article, explicit relations to calculate the local Nusselt number from the values corresponding to the boundary condition of the first kind have been developed for forced convective flow through asymmetrically heated parallel-plate channels. The asymmetric thermal boundary condition is characterized by a parameter, A, defined as the ratio of wall temperatures in excess of the entry fluid temperature. The boundary condition of the first kind corresponds to A = 0 or A -> infinity. The validity of the superposition relations has been established from the numerical results obtained for the simple model of hydrodynamically developed and thermally developing flow. However, the superposition relations can be expected to be valid, as long as geometric and flow symmetry are preserved.