Notes the large savings possible if ventilation were adapted to the prevailing need. A promising possibility for indicating occupancy and thus the ventilation requirement is measuring the level of carbon dioxide. The project includes a test with equipment for CO2-monitoring of the exhaust air flow in an office building which controls the volume of outdoor air supply, thusmaintaining the CO2 level constant. Measures how the CO2 level can vary locally,how other pollutants in air can vary, how much energy can be saved. Employees noted no significant difference between normal ventilation and CO2 controlled air flow. States the test proves the method works satisfactorily. Energy costs saved mean the equipment would pay for itself within about a year, depending on the design of the building. Currently available components are adequate for the system.