In my paper, I was observing the energy efficiency of Budapest Fasori Evanélikus Gimnázium. At first, I made an on-site monitoring in the building, in which I checked the energy consumers, and collected data about the energy usage. The school personnel helped me to get every information about the energy consumption. The economic department of the school made available to me the electicity bills and the gas bills for the years 2009, 2010, 2011 and 2012. I compared this data to the temperature diagrams of those years. I tried to make a detailed estimation of the energy usage of January 2012. The teachers and pupils helped me by answring my questionnaire about the temperature in the buiding, about their lighting and ventilation habits in a classroom. After that, I considered all of my collected data and observations and I made suggestions on reducing of energy and gas usage, and the cost cut availabilities. These prorositions comprise tariff change at the electricity supplyer company, lighting modernisation, solar system and heat pump system usage. All of my calculations include pay-off calculations as well. Finally, I recommended some simple opportunities, which don’t need any financial expenses to cut down the costs. I hope I could help the school to increase their energy efficiency, cut down the energy and gas usage along with the costs.