Parametric tests were experimentally conducted to observe the role of average nanoparticle size, pressure, heater orientation, and heater size during pool boiling of water using Al2O3 nanoparticle coated flat heaters. Results indicate that pool boiling performance is dependent on the parameters tested, except the nanoparticle size, for both uncoated and nanocoated surfaces. The nanoparticle coated heater consistently produced dramatic Critical Heat Flux enhancement relative to the uncoated surface at all tested conditions. It was postulated that the better wettability in the nanocoating, especially its ability to continuously rewet the base of the growing bubbles, was the main cause of enhancement. Published by Elsevier Ltd.