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 14,6 °C with about 650 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, approximately, 560 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. Several split air-conditioners are used for cooling in the summer. The common areas, the staircase, are heated with a gas flame coil. The primary energy consumption and total thermal energy demand is 277.800 kWh/year, which gives a value of around 200 kWh/m2 per year.