The aim of this study is to get the thermal characteristics of flow boiling using water at subatmospheric pressure compared to the atmospheric pressure to enhance the thermal performance of the system. The heat transfer rate, nucleation and critical heat flux are affected by the system pressure. The knowledge of subatmospheric pressure on flow boiling is desirable due to the growing demand for various applications. Flow boiling at the subatmospheric pressure is advantageous due to the relatively larger latent heat and relatively low surface temperature. The heat transfer coefficient and the surface temperature are investigated experimentally in a conventional tube at subatmospheric pressure for subcooled flow boiling. The water streams in the tube of diameter of 11.7 mm and a length of 1500 mm. The results are examined at different values of mass flux and heat flux at subatmospheric pressure. The effect of inlet subcooling and mass flux are explored in this study. It is evident from the experiments that the boiling heat transfer coefficient at subatmospheric pressure is greater than that observed at atmospheric pressure, for the subcooled flow boiling.