Heat transfer in a metal cut by a moving arc jet is considered using the method of superposition of heat sources and sinks. The heat sources are located at the plasma–liquid metal boundary, heat sinks—at the melting front. Special attention is paid to the influence of the molten metal layer that separates the plasma and not yet molten metal. It is shown that this layer hampers heat transfer to the melting front. Neglecting its heat resistance could lead to a very substantial errors especially at high cutting speeds. The thicker the layer and/or the higher the cutting speed, the more power is necessary to perform the cut and the higher the average temperature of the melt. Estimations show that power carried out by the removed melt could reach half of the total power necessary to make the cut. The suggested method allows one to include the heat of heterogeneous reaction of oxidation at the melting front. The method could be applied to describe other types of metal cutting with a moving concentrated heat source.