Abstract: An auxiliary heater for a vehicle heating system of the type having a burner projecting into a combustion chamber delimited by a combustion tube from which combustion gases emerge and are introduced into an annular space through which the combustion gases flow in an opposite direction to an exhaust outlet, the annular space being bounded peripherally by a heat exchanger containing a heat-transferring medium, such as water. In order to improve the efficiency of such an auxiliary vehicle heater and to lower the temperature of the combustion gases leaving the exhaust outlet, the cross-sectional flow-through area of the annular space is reduced in the flow direction toward the exhaust outlet. Fins are provided which project into the annular space a distance that reduces in correspondence with the reduction in the cross-sectional area of the annular space. The reduction in the cross-sectional area of the annular space may be continuous or in steps.

Abstract: A heater fired with liquid fuel, especially a vehicle heater, utilizing a liquid heat transfer medium. The heater comprises a tubular combustion chamber and a heat exchanger mounted over the combustion chamber. The heat exchanger deflects exhaust gas leaving the combustion chamber in an axial direction. An annular space, which conducts the hot exhaust gas, is left between the heat exchanger and the combustion chamber. The heat exchanger is provided with ribs on its inner lining which project into the annular space. These ribs are aligned essentially radially and parallel to a central longitudinal axis of the combustion chamber and the heat exchanger. To improve the efficiency of the heat exchanger, at least a portion of the ribs are provided with an exhaust vorticizing arrangement along at least a portion of their length.