These Guidelines recommend the ventilation required to obtain a desired indoor air quality in a space. The first step is to decide the air quality aimed for in the ventilated space. A certain air quality is prescribed to avoid adverse health effects while a decision is required on the level of perceived air quality aimed for in the ventilated space. Three different comfort levels are suggested. The next step is to determine the pollution load on the air caused by pollution sources in the space. The total pollution load is found by adding the loads caused by the building and by the occupants. The available outdoor air quality and the ventilation effectiveness of the ventilated space are also considered. The ventilation rate required to provide the desired indoor air quality is then calculated based on the total pollution load, the available outdoor air quality and the ventilation effectiveness. The ventilation rates required for health and comfort are calculated separately and the highest value is used for design.