A method of recovering heat from bottom ash that is discharged from a combustion process in a furnace. Fuel and combustion air are fed into a furnace for combusting the fuel in order to generate heat energy to produce at least one of steam and hot water in a boiler arrangement, in which flue gases and bottom ash are generated. The bottom ash is discharged from the furnace. Heat is recovered from the flue gases. Heat is also recovered to a bottom ash cooling circuit from the bottom ash discharged from the furnace in order to utilize the recovered heat for preheating the combustion air in a heat exchanger. The heat exchanger is arranged in a combustion air heating circuit. Heat is exchanged from the bottom ash cooling circuit to the combustion air heating circuit.