The paper investigates the effect of natural convection during differential scanning calorimetry measurements of phase change materials. We performed series of numerical simulations to characterize and quantify the perturbation on the measured thermogram. This perturbation becomes significant at the end of the fusion process. It manifests itself as an increase of the heat flux amplitude which accelerates the fusion process. Three correlations are built from the simulation results. The two first correlations quantify the amplitude of the heat flux deviation. The third correlation locates the time at which the perturbation occurs. The correlations are valid for large DSC capsules (around 1 ml), and high Prandtl materials (paraffins, salt hydrates, fatty acids). They enable to define the experimental conditions for which natural convection becomes negligible.