The increase Of CO2 emissions and the emerging climate change are the most serious environmental problems nowadays and limit economic development. This increase is mainly attributed to the growing world population and the related growth in energy demand, which results in the vast consumption of fossil fuels in the power generation sector. Significant actions for the implementation of energy saving measures have been adopted worldwide for reducing greenhouse gas emissions. CO2 calculators have been developed to evaluate the effectiveness of these measures, relating energy to CO2 emissions. These calculators include in most cases the entire power system. The purpose of this work was to evaluate the role of the electricity. networks' losses in the actual CO2 reduction potential, following the implementation of energy saving measures, in relation to the network's voltage level in which the infrastructure is connected. Buildings are representative due to their volume and to different voltage levels of power supply. The work presented was conducted in the framework of the Intelligent Energy Europe Programme entitled Bottom Up to Kyoto (BUtK), as a part of an evaluation of the CO2 emissions' reduction potential through energy savings measures in 6 municipalities of EU's New Member States. (C) 2009 Elsevier Ltd. All rights reserved.