The energy statistics of OECD Countries shows that between 30-50% of primary energy is consumed in non-industrial buildings (i.e. in dwellings, offices, hospitals, schools etc.) Of this, as much as 50% is dissipated from the building in the departing air stream. As buildings become more thermally efficient, the proportion of energy loss (either heating or cooling losses) associated with ventilation and air infiltration is expected to become the dominant thermal loss mechanism. Additional losses may be associated with the energy needed to operate mechanical ventilation systems.