Abstract: Heating boiler intended to be used for burning straw, paper and similar fuel material in the form of compressed bales. The boiler is capable of supplying the material to be burned as a function of the heat requirements. It is necessary to provide optimum combustion conditions to maintain exhaust gas emission values within prescribed limits. The boiler is therefore provided inside its combustion compartment with a channel (2) wherein the compressed bales are dried and the slow distillation gas is removed to a large extent from the fuel. The bale supply channel (2) opens into a combustion chamber (4) enclosing the combustion compartment and preventing the flames from touching the water jacket (15) of the boiler.