Within the context of the research programme “Koenst), a natural gas (methane) fuelled heater (Prototype I1) for injection moulding has been developed. When tested, the first prototype of this natural gas fuelled heater showed cracks at some specific spots, especially certain corners inside the hull. Studies showed that these cracks were caused by thermal stress components. A downscaled and re-designed prototype was produced (Prototype II), built for further validation under the appropriate test conditions. Unlike the first prototype, the re-designed prototype showed no cracks. Even though most of the problems were solved in this prototype, it was expected that the efficiency of the heater could be further improved. Aim of the study presented here was to improve the gas fuelled heater through a thermal and constructional re-design. The study has been carried out as part of the research programme “Ontwerpgereedschappen voor Extrusie” (Designtools for Extrusion).