The capability of simulating natural and forced convection has been recently developed and integrated into PowerFLOW, a general purpose CFD solver based on the lattice Boltzmann algorithm. Several benchmark tests have been performed to validate this buoyancy model. Two typical cases of Rayleigh-Benard convection with the Rayleigh number slightly above (Ra = 2000) and below (Ra = 1500) the critical Rayleigh number of 1708 were tested to verify the conceptual and algorithmic correctness of the buoyancy model. Then simulations of turbulent natural convection in an enclosed tall cavity with two different Rayleigh numbers, Ra = 0.86 x 10(6) and Ra = 1.43 x 10(6), were carried out and found to be in a very good agreement with the experiments of Betts and Bokhari. (C) 2004 Published by Elsevier Ltd.