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.