The present work reports a numerical study of natural convection in an incinerator shaped enclosure with a localized heated source situated at the bottom. Lattice Boltzmann Method (LBM) is used to simulate nanofluid (water-Al2O3) flow and heat transfer. Simulations have been carried out for the pertinent parameters: Rayleigh number (Ra=103−106 ), solid volume fraction 0 6%    relative heat source high ( 0 0.5    ), relative heat source width ( 0.02 0.8    ), and inclination angle of the incinerator ( 0 360     ). The comparison of the obtained results is in excellent agreement with results from literature. It may be noted that the Rayleigh number, the solid volume fraction, the heat source tallness enhances the heat transfer and influences the flow pattern and the thermal structures. However for the relative heat source width plays opposite role for values superior to 0.4.