Natural convection is simulated in a truncated cone filled with Cu-water nanofluid, pure water is considered as the base fluid with Pr=6.2 and (Cu) is the nanoparticle . Inclined and top walls have constant temperature where the heat source is located on the bottom wall of the conical container which is thermally insulated. A finite volume approach is used to solve the governing equations using the SIMPLE algorithm for different parameters such as Rayleigh number (103, 104, 105 and 106), inclination angle of inclined walls of the enclosure and heat source length (0.3L, 0.7L and L). The results showed an enhancement in cooling system by using a nanofluid, when conduction regime is assisted. The inclination angle of inclined sidewall and heat source length affect the heat transfer rate and the maximum temperature.