Heat exchanger with a optimised fluid flow heat absorbing channel, in particular for heating apparatus

Heat exchanger comprises a base body (10) with a heat-releasing flow channel (19) for a heat-releasing medium and a heat-receiving flow channel (25) for a heat-receiving medium. The heat-receiving flow channel has different flow cross-sections along its spiral-like extension so that the flow speed of the heat-receiving medium fits the heat load of the corresponding region of a heat transfer wall (11). Preferred Features: Windings (25.1-25.8) are formed on the outer side of the heat transfer wall to form the heat-receiving channel. The cross-section of the windings is fitted locally to the heat load of the corresponding region of the heat transfer wall.