Two-dimensional numerical simulations of the natural convection flow of air in a differentially heated, inclined square cavity were performed for both laminar and turbulent flows. The angle of inclination of the cavity was varied from 0°(heated from below) to 180°(heated from above). For Rayleigh numbers between 10 4 and 10 11 the natural convection flow has been calculated. A detailed analysis was made for Rayleigh numbers of 10 6 and 10 10. The standard k− ε model for turbulence was used in the prediction of turbulent flows. Numerical predictions of the heat flux at the hot wall and the influence of the angle of inclination on the Nusselt number are presented. The Nusselt number shows strong dependence on the orientation of the cavity and the power law dependence on the Rayleigh number of the flow. Flow patterns and isotherms are shown to give greater understanding of the local heat transfer. For the high Rayleigh number calculations hysteresis of the solution was found at a transition of flow patterns.