Laminar free convection in an isothermal asymmetrically heated vertical channel has been extensively studied in the past, and empirical correlations for the overall channel convective heat transfer rate are available in the literature. However, this problem has been revisited in order to develop empirical correlations that allow the calculation of the average Nusselt number for each channel wall separately. A numerical solution has been obtained for a Prandtl number of 0.71 and for Rayleigh numbers ranging from the conduction regime to the isolated boundary layer regime. The data have been used to develop correlations for the average Nusselt numbers on the hot and cold walls. These correlations satisfy a heat balance for the overall channel.