Over the past decades, pool boiling heat transfer of water has been investigated extensively by many scientists and researchers at system pressures varying from atmospheric to near critical pressure. However, at sub-atmospheric pressures conditions there is a dearth of data, particularly when the vapour pressures are less than 10 kPa. The authors have conducted a detailed study of pool boiling of water in an evaporator where its system pressure was about 1.8 kPa. The heat flux for pool boiling was derived from an uniform radiant heaters up to 5 W/cm2 (or a total heating rate of 125 W within an area of 25 cm2), a region that is of interest for the cooling of CPUs.