Laminar mixed convective flow across a block-mounted plate in a vertical channel is studied numerically. One plate with blocks is elevated to a constant temperature different from the inlet air and the other is adiabatic. The results show that the local Nusselt number is significantly affected by secondary flows induced by buoyancy and channel geometry. It is also noted that the heat transfer is mainly a function of the three geometric ratios and the Reynolds number. The average Nusselt numbers decrease with increasing Gr/Re2values in the blocks and increase with Gr/Re2at high Grashof numbers in the recirculation zones.