An intake plenum unit is provided for a heat exchanger with a tube block made of a plurality of heat exchanger tubes. The heat exchanger incorporates an intake plenum with a tube wall in which a lengthwise slot is provided for receiving ends of the heat exchanger tubes. The intake plenum is made of one or more individual tubes inserted into one another endwise or fitted together. Each intake plenum has, at least at one individual tube end, a lengthwise slot that is open and made before or after the construction of the intake plenum. This allows problem-free compensation for manufacturing tolerances of the tube ends to be fitted into the lengthwise slot regarding their length in the direction of the lengthwise slot. The intake plenum unit is suitable for use, for example, for gas coolers and evaporators of carbon-dioxide air conditioners.