Since the CO

2-emissions and electricity prices are ever increasing many companies have tried to reduce their energy consumption in order to reduce both CO2-emissions and the cost of using energy. Therefore, in this article an office building situated in Sweden have been investigated with its current ventilation flow and what saving poten-tials can be made from heat recovery and a different ventilation flow in regards to health, energy and cost. Empirical data have been collected to be able to calculate ener-gy savings made by heat recovery and new ventilation flow. A ventilation flow of 25 l/s per office were chosen and that the conference room should have at least 3 l/s per m² the dining room and locker was not investigated thoroughly and therefore a ventilation flow from the recommendations of Sweden was followed. The total flows became, 530 l/s respectively 630 l/s for the top and bottom floor. A rotating heat exchanger with an es-timated efficiency of 80% was used for heat recovery and through the two methods combined an energy reduction up to 96,4 % for heating and 83,4 % from the electricity could be reduced.