Tips to simulate natural convection in a closed domain: Mass conservation inside the closed volume of simulation could be numerically hard to achieve particularly if the steady state solver is used. The choice of a proper density model for the purpose is crucial: For steady solver, the mass of the domain is related to the operating density (constant) and in that case the Boussinesq model must be used (no equation of state). If the transient solver is used, for instance if no steady state results could be obtained (weak convergence), both ideal gas and boussinesq model could be recommended; initial conditions prescribe the mass inside the closed domain. Ideal gas model should be preferred if large density variations (>20% change) are expected inside the domain. In any closed domain case, the incompressible ideal gas model should not be used since pressure inside the closed domain is adapted locally in such a way that the mass is conserved.