Most of the energy consumed worldwide comes from non-renewable sources, such as oil derivatives, making it necessary to search for renewable, clean energy sources, with emphasis on biomass from agricultural and industrial waste. Coconut shell pellets (CSPs) and cashew nut shell pellets (CNSPs) were manufactured and subsequently subjected to chemical, thermal and exhaust gas analyses of their combustion. Mean temperature results in the combustion area were 366.44 ± 84.79°C (CSPs) and 295.00 ± 89.47°C (CNSPs). The exhaust gas combustion values were 19.43 ± 0.57% (CSPs) and 18.75 ± 0.77% (CNSPs) of O2, 2348 ± 1241 ppm (CSPs) and 2901 ± 499 ppm (CNSPs) of CO, 14.92 ± 5.06 ppm (CSPs) and 39.83 ± 10.91 ppm (CNSPs) of NOx, and 441.25 ± 130.41 ppm (CSPs) and 2841.50 ± 765.26 ppm (CNSPs) of CH4. In conclusion, the combustion process of CSPs proved to be less polluting and more energy efficient when compared with CNSPs. The analyses of the exhaust gases from the combustion of these biomasses can serve as a basis for the creation of safety parameters and public policies to regulate the use of biomass for energy purposes.