Convective heat transfer must not be necessarily generated by an external induced flow. When density in a fluid varies with temperature, gravity forces act on the density variations inducing a flow. This effect is called buoyancy. Buoyancy-driven heat transfer is termed natural convection. This type of flows are highly unsteady, such that conventional CFD methods that rely on a time-averaged approach fail to obtain a converged solution. For this reason I use LES to simulate the transient behavior of natural convection flows.