In this study, the energy performances for the insulated and uninsulated statuses of a building located in Selcuklu district of Konya were determined and compared. The energy efficiency of the insulated and uninsulated building was examined using the Building Energy Performance Program (BEP-TR 2). In addition, the results obtained from this program was compared with the results obtained from TS-825 and was interpreted. Within the scope of the study, the project information of the building (geometry of building and heating, lighting, mechanical and ventilation system information) was entered into the BEP-TR Program, and clear energy amounts for the heating and cooling needs of the building were determined. Besides, the need of lighting energy, the amount of consumption and the emission amounts of carbon dioxide (CO2) were determined in the days when the daylight was not utilized and in the areas that had no effect on daylight. Heat loss and heat gain calculations of the building have been made, according to TS-825. In consequence of the data obtained, the annual heating energy need of the insulated building was determined as 92 kWh/m² and the energy class was determined as C class, with the BEP –TR program. However, the annual heating energy need of the uninsulated building was 134 kWh/m² and the energy class was determined E class.