In large part of the World, people spend more than 90 percent of the time in indoor environments, where air quality is important for health. The environment outside the building, what goes on inside the building and the exchange of air pollutants affects the indoor air. Tight buildings can reduce energy consumption and entry of outdoor air pollutants, but unless ventilation is right indoor air pollutants from combustion processes, dampness, microbes, the dwellers bio effluents, appliances, care and cleaning products, clothing, furniture, building materials, the underground and many other sources will build up indoors causing important health effects.