Why Ventilate your Home,
Paraphrased from Rob Dumont:
Every house needs ventilation. Most older houses get their ventilation from air leakage, but most modern houses on the are now tight enough that a mechanical ventilation system is needed.
Why do houses need ventilation? Let’s go back to fundamentals.
There are about five main reasons. First, people need about 8 Litres per second (15 cubic feet per minute) of reasonably clean air for health and comfort. We ingest air at about 380 parts per million outdoors and our lungs reject carbon dioxide into the air that we exhale. Our exhaled breath is quite loaded with carbon dioxide, with about 40,000 parts per million or 4% CO2 . If you recycled that exhaled breath directly back into your lungs, you would soon be overcome with carbon dioxide poisoning. This is essentially what happened in the Black Hole of Calcutta, when a large number of people died in a confined space. Inside houses and most buildings, carbon dioxide levels should generally be below about 1000 parts per million. If the level is higher, it is usually a sign of inadequate ventilation (or a blocked chimney.)
A second reason that humans must have ventilation is to get rid of moisture that the body emits. Sedentary adults release about 0.1 kilogram (0.1 litres) of moisture per hour, partly through breathing and partly through skin evaporation. Cooking, bathing, floor washing, etc. all contribute additional moisture to the air. One of the common signs of inadequate ventilation in a home is high humidity, with condensation on the windows.
A third reason for ventilation is to dilute body odour, perfumes, deodorants, cologne, etc.
A fourth reason to ventilate is to remove the offgassing from building materials. Our paints, floor coverings, furniture, cabinets and so on all will all emit some volatile organic compounds, and these should be diluted by adequate ventilation. It is also important to choose building materials carefully to avoid organic compound emissions and formaldehyde.
A fifth reason to ventilate is to ensure that there is adequate combustion air for furnaces, boilers, water heaters, fireplaces, etc. When any fuel burns, sufficient air must be supplied or deadly carbon monoxide can readily occur.
In older houses, leaky walls and ceilings will generally provide enough ventilation air through most of the year. However, when there is no wind and the temperature inside the house is the same as outdoors, there is no driving force for ventilation, and very little air change will result.
