Natural convection in partitioned square enclosures filled with air is numerically studied, trying to characterize these enclosures mainly in what concerns its overall heat transfer performance. Two partitions of finite thickness are considered, placed in the enclosure following an ordered arrangement, which position, length and thermal conductivity are varied for some values of Rayleigh number and for different thermal boundary conditions. Study starts considering the simplest enclosures with two adiabatic partitions, after the more realistic enclosures of heat conductive walls and partitions are considered, and finally the even more realistic situation of enclosures with heat conductive partitions and walls subjected to cyclic thermal boundary conditions in the vertical direction is also considered. Position and length of the enclosures' effects depend on the thermal boundary conditions prescribed for the enclosure, and different thermal boundary conditions (corresponding to the heating or cooling operations or seasons) are considered to capture this effect. Fluid flow field, thermal field and heat transfer are analyzed for some particular situations through the streamlines, isotherms, and heatlines. The overall thermal performance of the enclosure is analyzed through the overall Nusselt number, and many data are compactly presented for different placements and lengths of the partitions, for different thermal conductivity of the walls and partitions of the enclosure, for different Rayleigh numbers and for different thermal boundary conditions imposed to the enclosure. Considered boundary conditions and the enclosure walls and partitions of finite thickness and finite thermal conductivity are much more realistic conditions than simply the single cavity without walls and with perfectly adiabatic partitions usually considered in many studies of this kind. (C) 2012 Elsevier Ltd. All rights reserved.