This work presents numerical computations of heat transfer over banks of square rods in aligned and staggered arrangements with porosity in the range 0.44-0.98. It is focused on low Reynolds number flows (0.05-40). Two thermal boundary conditions were investigated, namely constant wall temperature and constant volumetric heat source. The effects of bank arrangements and porosity as well as the effects of Prandtl and Reynolds numbers on the Nusselt number are examined. In the case of constant volumetric heat source, the results are approximated with a power equation adapted for the case of low Re number flows. This study shows that the thermal boundary condition on the solid surface influences heat transfer when thermal equilibrium is reached in the bank of rods. (C) 2007 Elsevier Ltd. All rights reserved.