To bring in oxygen. All living beings consume oxygen. Breathing turns oxygen into carbon dioxide (CO2), which can cause headaches, tiredness and concentration issues. Ventilation removes carbon dioxide from the house while introducing fresh air.
To control humidity. Human activity creates humidity (breathing, baths, showers, cooking, laundry). For example, a family of four can release about 20 litres of water vapour in the air of the home every day. Excess moisture is harmful to several materials and objects because it can cause expansion, loss of adhesion, odours, oxidation (rust), mould, rotting and condensation. Ventilation evacuates this excess water vapour. On the other hand, insufficient moisture dries out our respiratory system and makes us vulnerable to viruses and bacteria. Low humidity levels can also cause wood to crack. As shown in graph the ideal humidity level is between 40% and 60%, or 35% if the outside temperature is close to -20°C (-4°F) or lower.
