Energy saving is a highly concerned topic in the developing countries. To achieve a desirable living and working condition for inhabitants while consuming minimum amount of energy, more and more efforts, new technologies are developed and invested in the different industries by countries. It has been discussed that energy use in the building sectors is intensive and has the largest share in the total energy supply. Therefore, a growing number of companies and institutions are either required or voluntary to take energy efficiency measures once a year or more to identify current energy use, as well as the opportunities for energy efficiency improvement. One of the energy efficiency measures is energy audit. This report is aiming at pinpointing the current energy consumption for a joint ventilation system used by five premises in downtown Gävle, Sweden. The building company is planning a renovation for the ventilation system, including a cut down of energy supply while improving thermal comfort by providing adequate ventilation. The main object area is a restaurant, which consumes most energy supply. During the measurements, three sets of equipment (TSI VelociCalc plus, SWEMA FLOW 230 and TSI-AccuBALANCE) were used to collect air flow and temperature data. The results indicate that the current energy use for the joint ventilation system during a year is around 50438 kWh, using recommended ventilation rates; while it can be reduced to 34737 kWh. For the restaurant, the required ventilation rate is 1204 l/s to provide fresh air constantly if it is over 150 people and give ventilation according the standard: 7 l/s p 0.35 l/s m2. The current ventilation rate is only 312 l/s, thus clearly failing to comply with the standard. One viable method for providing enough ventilation rate and at the same time without wasting energy is to install CO2 detector, which regulates the ventilation rate according to the level of CO2 concentration. The studied shops have instead very high ventilation rates in the current system; though this provides good air quality, the energy is wasted unnecessarily.