The paper reports experimental and numerical investigation of the melting front propagation in a paraffin-based phase change material (PCM). The investigated case was a block of PCM with a heat flux introduced at one of its sides. The PCM block was contained in a transparent container and thus the propagation of the melting front could be monitored with a camera. The melting temperature of the PCM was 28 °C and the container was located in an environmental chamber where the ambient temperature was maintained at 27 °C during the experiment. The natural convection in the melted PCM played an important role and it had to be considered in the heat transfer models. The numerical models taking into account natural convection in liquid PCM require long computation times, and therefore they are impractical if the fast computation of the melting front position is needed. The effective heat conductivity approach can be used to overcome this issue. Two numerical models were compared: an in-house heat transfer model using effective conductivity approach developed in MATLAB and a more advanced model created in the off-the-shelf simulation tool COMSOL, which accounts for the natural convection in liquid PCM.