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.

A typical energy balance of an apartment building is presented in Figure 1. The heat loss due to ventilation and infiltration appears to be reasonably small, averaging 0.5-0.7 air changes per hour.

Heat recovery systems are not common, partly because of high investment costs (as they require either a heat pump system or a mechanical supply air system).