Endothermic (in the 30-300 C range) and exothermic (in the 300-500 C range) processes were identified through differential scanning calorimetry experiments on fly ash in an air atmosphere. The endothermic processes are thermodynamically controlled and include the desorption of organic compounds along with a phase transition. Instead, exothermic processes are kinetically controlled and include two distinct combustion reactions. Their nature was confirmed by the flatness in DSC scans performed in nitrogen. The apparent activation energies of the two reactions are in very good agreement with those previously obtained from kinetic studies. Based on these laboratory experiments, the energy balance of the thermal process on the fly ash was performed.