An experimental study has been performed to investigate the forced convection heat transfer around a tube in six scale-deposited circular cylinders of staggered arrangement in a cross-flow of air. The local, mean Nusselt numbers and fouling resistance were estimated. The effects of the scale thickness, the cylinder spacing and Reynolds number were studied to clarify the heat transfer characteristics and compared with those of in-line tube bank. The results are compared with that of clean cylinder. Subsequently, the mean fouling resistance over the entire circumference was estimated from those results as a function of scale thickness, the cylinder spacing and Reynolds number. It is found that the heat transfer of staggered tube banks greatly varies with the fouling of water scale, especially its height. Further, the mean fouling resistance strongly depend upon the cylinder spacing and Reynolds number. Copyright (C) 2003 John Wiley Sons, Ltd.