This study deals with an exergetic performance evaluation of a geothermally heated building. This building used in the analysis has a volume of 1147.03 m(3) and a net floor area of 95.59 m(2), while indoor and exterior air temperatures are 20 and 0 degrees C, respectively. The geothermal heating system used for the heat production was constructed in the Ozkilcik heating center, Izmir, Turkey. Thermal water has a pressure of 6.8 bar, a temperature of 122 degrees C and a mass flow rate of 54.73 kg/s, while it is reinjected at 3.2 bar and 72 degrees C. The system investigated feeds three regions. Among these, the Ozkanlar region has supply/return pressure and temperature values of 4.6/3 bar and 80/60 degrees C, respectively. Energy and exergy flows are studied to quantify and illustrate exergy destructions in the overall system. Total exergy input rate to the system is found to be 9.92 kW and the largest exergy destruction rate occurs in the primary energy transformation at 3.85 kW. (C) 2008 Elsevier Ltd. All rights reserved.