This residential building is located in Boyana, a neighbourhood of the Bulgarian capital Sofia. The climate in Boyana is warm and temperate. The average annual temperature is 10,6 °C with about 600 mm of rainfalls annually. The building is a two-floor multi-family 6 apartment dwelling that was completed in 1974. In 2004, a new part was added to the building. Total floor area is 564 m2. In the new part, gas boilers provide hot water and space heating. In the old part separate electric boilers and heaters carry out these functions. Split air-conditioners are used for cooling in the summer. The common areas are heated with a gas heater. The annual final energy consumption related to the occupied apartments with a heated space of 336 m2 is 200 kWh/m2, of which 143 kWh/m2 from natural gas, 13 kWh/m2 from coal and 44 kWh/m2 from electricity. The annual heating and cooling demands are 117 kWh/m2 for space heating, 21 kWh/m2 for DHW and 58 kWh/m2 for space cooling.