The purpose of ventilation is to remove the poor, humid air from your home and to replace it with fresh, temperate and filtered air. Ventilation means continuous air exchange. With a ventilation system, the air is replaced automatically, in contrast to manual ventilation, which requires open windows, and some times carries the risk of drafts and other inconveniences.
A family of two adults and two children produces around 10 litres of liquid a day, which needs to be ventilated out of the home. The Danish Asthma and Allergy Association recommend that homes are aired out for 3 x 5-10 minutes daily, with a through draught, all year round to expel damp and harmful particles. This is not necessary with mechanical ventilation. At the same time, you also save on heating bills, as the heated air does not disappear out the window in winter.