This study investigates the combined effects of surface roughness, slope, and CuO nanoparticles on enhancing the heat transfer coefficient (HTC) in pool boiling. The thermal behaviors were examined across both the free convection and nucleate boiling regimes. Results indicate that surface roughness and slope significantly influence heat transfer performance. Furthermore, the addition of CuO nanoparticles, together with the surface parameters, influences the heat-transfer behavior under the investigated conditions.The best-performing conditions among those investigated were identified as 0.1 wt% nanoparticle concentration, 0.94 µm roughness, and 10° slope for the free-convection regime, and 0.1 wt% nanoparticle concentration, 0.71 µm roughness, and 20° slope for the nucleate-boiling regime.Under these optimum conditions, the HTC increased by 53.4% and 45.4% in the free convection and nucleate boiling regimes, respectively. Additionally, the transition time to nucleate boiling was reduced by 12.3% through surface modifications and by 22.3% due to the presence of nanoparticles. Finally, the experimental setup and data were validated against existing literature, demonstrating high accuracy.