An assessment of the contribution from the discharged air from the ventilation unit (after the passive heat exchanger) is not defined in the regulations.
As such, the combined unit needs to be tested as prescribed by the regulations on space heaters, water heaters and ventilation units and the relevant standards. If the mentioned contribution is not considered in the Regulation or harmonised standards, then it cannot be taken into account.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.