To overcome the limitations of traditional machining processes, a new foam machining process, the so-called rapid heat ablation (RHA) process using a rotary hot tool, was proposed as rapid prototyping and manufacturing (RPM) technologies. In this paper, the thermal characteristics of rapid heat ablation for EPS foam are investigated through numerical analyses. As the first approach, the thermal field by a stationary heat source is analyzed in order to demonstrate the influence of the tool shape and isotropy of a thermal field. Based on the analysis for stationary heat source, the rotary hot tool can be assumed to be a volumetric heat source. Thermal fields of workpiece by moving the heat source are simulated with valid assumptions and thermal boundary. As a result, the model predicts the temperature distribution of the workpiece as well as the melting zone which is the above melting temperature for various process parameters. The melting zone determines the calculated kerfwidth. The calculated kerfwidth shows a good agreement against the kerfwidth obtained by the experiment.