This study investigates the natural convection in a square enclosure with hot and cold cylinders, induced by the temperature difference between a cold enclosure and the hot and cold circular cylinders contained within it. The immersed boundary method is used to model the two enclosed cylinders, based on the finite volume method, and two-dimensional natural convection was studied for different Rayleigh numbers in the range 10(3) <= Ra <= 10(6). Additionally, the study investigates the effect the presence of the hot and cold cylinders at different locations within the enclosure have on the heat transfer and fluid flow. The locations of the hot and cold circular cylinders are varied vertically along the centerline at the left and right parts of the enclosure, respectively. The existence of local peaks for the Nusselt numbers along the surfaces of the cylinders and enclosure is determined by the gap between the cylinders and the enclosure and thermal plume governed by the convection, respectively. Detailed analysis results for the distributions of the streamlines, isotherms, and Nusselt numbers are presented in this paper. (C) 2012 Elsevier Ltd. All rights reserved.