<p>Mostly, earlier studies on heat transfer enhancement through surface modifications have concentrated on understanding thermal energy transfer in forced convection regimes, while research on surface modification for enhancing heat transfer under free convection regimes has been relatively sparse. Moreover, while surface modifications affect the emissivity of a surface, this effect was not reported in earlier studies on heat transfer from micro/nano-scale coated surfaces. This investigation aims to quantify the contribution of individual heat transfer mode to the overall heat transfer, comprising free convection and thermal radiation, from surfaces modified by thermal spray coating technique. Additionally, the study examines the influence of non-uniform microstructure of the surface coating on enhancing heat transfer from these modified surfaces. The results show that the surface coating has caused to reduce the wall temperature by 29.71K with aluminum oxide micro particles and by 28.23K with tungsten micro particles, in comparison to the temperature of an untreated copper plate. The enhanced heat transfer from the plates coated with microscale particles is the result of synergistic effects of improved convective and radiative heat transfer. Our findings reveal that when considering natural convection from microscale-coated surfaces, thermal radiation is a significant factor in heat transport. Therefore, neglecting it can lead to misleading qualitative and quantitative result. Thermal radiation contributes as much as 49 % to the total heat transfer at high heat loads for surfaces coated with aluminum oxide and tungsten micro-particles. The newly proposed heat transfer correlations highlight the significance of surface roughness and emissivity in estimating conjugate heat transfer from surfaces coated with microscale particles.</p>