Why do you need a ventilation system in a Passive House Building?

A lot of energy is required to heat air, or cool it during summer, yet very little energy is needed to move air around via an efficient fan. Therefore in order to achieve low energy use in a building, air leakage has to be minimised or the heating energy you pay for just ends up leaking outdoors. All Passive Houses must achieve a stringent airtightness requirement. Certified Passive House ventilation units have exceptional energy efficiency and are highly recommended.