A heating device for an exhaust system of an internal combustion engine ; the heating device comprises: a first tubular body where a combustion chamber is obtained on the inside; a fuel injector , which is mounted through a first base wall of the first tubular body so as to inject fuel into the combustion chamber ; at least one inlet opening , which can be connected to a fan so as to receive an air flow, which is directed into the combustion chamber and mixes with the fuel; a hot air outlet opening to let hot air out of the combustion chamber , which outlet opening is obtained at a second base wall of the first tubular body opposite the first base wall ; an outlet duct , which originates from the outlet opening ; a spark plug , which is mounted through a side wall of the first tubular body so as to trigger the combustion of a mixture of air and fuel; and a labyrinth , which surrounds a side wall of the first tubular body , starts from the inlet opening , ends in the combustion chamber and must necessarily be crossed through by the air that, from the inlet opening , reaches the combustion chamber ; wherein the labyrinth comprises a delivery segment , which develops around the first tubular body and extends from the inlet opening at the first base wall of the first tubular body , to an annular manifold , which preferably surrounds the outlet duct ; and the heating device is characterized in that: the delivery segment develops only around half of the first tubular body ; and the labyrinth comprises a return segment , which develops around a remaining half of the first tubular body that is not engaged by the delivery segment , has no point overlapping with the delivery segment and extends from the annular manifold to the combustion chamber . a first tubular body where a combustion chamber is obtained on the inside; a fuel injector , which is mounted through a first base wall of the first tubular body so as to inject fuel into the combustion chamber ; at least one inlet opening , which can be connected to a fan so as to receive an air flow, which is directed into the combustion chamber and mixes with the fuel; a hot air outlet opening to let hot air out of the combustion chamber , which outlet opening is obtained at a second base wall of the first tubular body opposite the first base wall ; an outlet duct , which originates from the outlet opening ; a spark plug , which is mounted through a side wall of the first tubular body so as to trigger the combustion of a mixture of air and fuel; and a labyrinth , which surrounds a side wall of the first tubular body , starts from the inlet opening , ends in the combustion chamber and must necessarily be crossed through by the air that, from the inlet opening , reaches the combustion chamber ; wherein the labyrinth comprises a delivery segment , which develops around the first tubular body and extends from the inlet opening at the first base wall of the first tubular body , to an annular manifold , which preferably surrounds the outlet duct ; and the heating device is characterized in that: the delivery segment develops only around half of the first tubular body ; and the labyrinth comprises a return segment , which develops around a remaining half of the first tubular body that is not engaged by the delivery segment , has no point overlapping with the delivery segment and extends from the annular manifold to the combustion chamber . the delivery segment develops only around half of the first tubular body ; and the labyrinth comprises a return segment , which develops around a remaining half of the first tubular body that is not engaged by the delivery segment , has no point overlapping with the delivery segment and extends from the annular manifold to the combustion chamber . <EOS>