A downward-facing heating surface under a pressurized condition is expected in some systems, such as in in-vessel retention through the external reactor vessel cooling (IVR-ERVC) or core catcher strategies, that are adopted in nuclear power plants. Because carbon steel is used in the IVR-ERVC strategy and some core catcher candidates, the combined effect of orientation, dimension, pressure and material effects on the CHF results had to be defined. In this study, the combined effects have been addressed with pressure up to 10 bar. The experimental results show that the trends are affected not by an independent parameter, but strongly affected by several environmental conditions. Different trends could be observed between the carbon steel and the stainless steel under high-pressure conditions. In addition, the effect of width on the CHF decreased and sometimes reversed as the pressure increased. Overall CHF on carbon steel is higher than that of the stainless steel at all width, pressure and inclination angle conditions. When the material effect combined with the pressure effect was considered, the trend could be divided into the following two conditions: narrow and wide. Based on the experimental trends, to apply realistic data, operational conditions including pressure condition should be considered, and other parameters such as material properties should also be considered to explain the trends.