The ventilation systems in residential buildings are built so that external air is directed into living rooms (living rooms and bedrooms) and air is drawn out of the so-called dirty rooms (kitchen, WC, laundry room, bathroom, wardrobe). Air thus moves from the clean rooms toward the dirtier rooms. Ventilation must be in continuous operation at minimum capacity at the least. The building will constantly need general ventilation which removes volatile substances from construction and finishing materials. In addition, ventilation will be required to replace the air contaminated by human and other activity with fresh air from outside. Ventilation in a home is sufficient if the room in living areas is replace completely every two hours. In addition, failure to clean ventilation is one of the primary causes of mould problems.
The purpose of ventilation is to ensure healthful and pleasant indoor air in a building. The ventilation system removes contamination in the air and brings in fresh air from outside. Contamination in this case includes odours and moisture from human activity, radon from the soil, and chemicals from construction and finishing materials.