This study presents energy efficiency measures in fans as an important energy consumption facility in the industry and common usages by identifying the sources of energy loss and applying methods to reduce those losses, which are one of the critical issues in protecting the environment and in global warming. The carbon footprint can be lowered by reducing the energy consumption of a fan over its life cycle. The main sources of energy loss in fans such as noise, vibration, lubrication, temperature of the bearings, installation type, damper and filter, especially pulley and belt system compared to electrical variable speed drive, are theoretically and experimentally discussed. The laboratory results show that the mechanical variable speed drive is one of the critical sources of energy loss in centrifugal fans. The results also show that by changing the drive with an electrical variable speed drive, the energy usage can be substantially optimized. For instance, using an electrical variable speed drive has reduced the energy loss up to 38.5 % with regard to the speed and according to the different flow rates. Moreover, based on the results derived from the equations and figures, it can be concluded that a considerable amount of energy per year, as well as the related cost can be saved and this shall be noted particularly in industrial applications.