The present invention relates to a system for extracting and recovering energy for large for large flows of heavy ashes produced by solid fuel boilers, able to decrease the final temperature of the extracted ash without increasing the air flow entering the boiler flue, usually fixed by the boiler designers at a value around 1.5% of the total combustion air. When the air flow needed to the cooling exceeds the maximum quantity allowable in the boiler, the system allows the exceeding air and the possible vapour to be sent to the air inletting duct entering the air/fume exchanger on the air side, thanks to a separation of the cooling environments made by the ash itself. The separation of the environments of the cooling system is handled automatically based upon a temperature signal of the ash to the discharge from the system. If the cooling air is not sufficient to cool down the ash, the cooling efficiency can be increased by the addition of nebulised water.