Free convective heat transfer for laminar, two dimensional flow in a vertical channel with a backward-facing step on the heated plate with isothermal boundary conditions has been numerically analyzed. The results compare favorably with the existing numerical results for a plane channel as well as for a backward-facing-step. The velocity distribution shows starved flow situations after the step for a Rayleigh number of 103 and higher for a step size of 50% of the plate spacing for asymmetric heating. For a step size of 25% of the plate spacing such situations were observed for Rayleigh numbers of more than 2000. Recirculation starts to disappear as the straight wall temperature approaches the inlet fluid temperature for a step size of 50% of the plate spacing.