The research community as well as the design and construction practice is spending a lot of efforts and investments in developing systems which optimise the energy use for achieving certain specified air flow rates. For example, improvements in efficiencies of 10 % in heat recovery systems would be considered as remarkable. At present, one observes a tremendous difference in the ventilation requirements in various countries as well as at the European level. Variation of a factor 10 of the ventilation rate requirement can be found in the proposal for European standard CEN prENV 1752 depending on the 'cleanness'of the building. The present paper develops these problems and makes a comparison with the situation in other areas like thermal comfort and lighting requirements.