The invention relates to a heating unit, particularly a tube radiator, comprising at least two layers of heating elements (9) for receiving and conducting the heating medium, at least two heating elements (9) being disposed next to each other in each layer of heating elements (9). Said heating unit further comprises a supply connection for feeding the heating medium and a return connection for discharging the heating medium. According to the invention, feeding means (25, 27, 29) are provided which supply the heating medium from the supply connection to one of two layers of heating elements (9) (supply layer) if the heating unit encompasses two layers of heating elements (9) or to one or both of the most external layers (9) (supply layers) of heating elements if the heating unit encompasses at least three layers of heating elements (9). The inventive heating unit (1) is configured such and the final areas of the heating elements (9) of the at least two layers of heating elements (9) are connected such that at least some of the heating medium penetrates the heating elements (9) of the other layers of heating elements (9) in the opposite direction of flow after penetrating the heating elements (9) of one or both supply layers.