This study deals with an exergetic analysis and assessment of a low exergy heating system from the power plant through the ground-source heat pump to the building envelope. The methodology used is based on a pre-design analysis tool, which has been produced during ongoing work for the International Energy Agency (IEA) formed within the Energy Conservation in Buildings and Community Systems Programme (ECBCSP) Annex 37 to increase the understanding of exergy flows in buildings and to be able to find possibilities for further improvements in energy utilization in buildings. The analysis is applied to a room with a volume of 105 m(3) and a net floor area of 35 m(2) as an application place, while indoor and exterior air temperatures are 20 degrees C and -15 degrees C, respectively. The heat pump system used for heat production with a maximum supply temperature of 55 degrees C was designed, constructed and tested in Aksaray University, Aksaray, Turkey. In this context, energy and exergy flows were investigated, while exergy destructions in the overall system were quantified and illustrated. Total exergy input of the system was found to be 7.93 kW and the largest exergy destruction occurred in the primary energy transformation at 5.31 kW. (C) 2008 Elsevier B.V. All rights reserved.