Abstract The effect of carbon nanotubes (CNTs) on nucleate boiling heat transfer in R22 and water is investigated with the addition of 1.0 vol% of CNTs. Test results showed that CNTs increase boiling heat transfer coefficients of these fluids. Especially, large enhancement up to 28.7% was observed at low heat fluxes of less than 30 kW/m 2. With increasing heat flux, however, the enhancement was suppressed due to vigorous bubble generation. Fouling on the surface was not observed during this study. Optimum quantity and type of CNTs and their dispersion should be examined for their commercialization in power plants and refrigeration equipment.