The influence of airtightness on the operation of ventilating systems in multi story buildings.

Energy consumption due to ventilation and air infiltration has been estimated to be 30-50% of the total energy use in Finnish high rise residential buildings. While natural ventilation was common in earlier buildings, central mechanical ventilation systems have become predominant during recent decades. Presents a typical energy balance in an apartment building. The heat loss due to ventilation and infiltration appears to be 0.5-0.7 ach.