A CO2 level of 1000 ppm is very often used as reference for control and design of ventilation flow rates in buildings. This level is well accepted in practice, and is thus normally not given any further considerations. To retain 1000 ppm CO2 in a room with fully mixed flow conditions, a flow rate of 7 liters/sec per person must be supplied. In many countries, national regulations and standards prescribe flow rates for comfort ventilation that are significantly higher than 7 l/s. This is because ventilation flow rates are not related to occupancy alone, but also for instance to emission of odour and chemicals from building materials, activities and ongoing processes in the buildings. Ventilation requirements due to emission from building materials and processes are added to the occupant related flow rate. Hence, to meet regulations and standards while controlling CO2, the set point must be lower than 1000 ppm. This paper focuses on how to determine set points to meet the regulations. Norwegian building regulations have been used as an example. Calculations show that the set points can vary greatly from room to room, dependent on occupant load, room type and application, outdoor air quality and emission rate from building materials.