Carbon dioxide emissions during the application of the heat pump in selected European countries for one hundred years are estimated. These emissions were calculated including the source of the electrical energy. The highest emissions are in Macedonia and Poland, where coal and lignite are the major sources of electrical energy. The lowest emissions are in Norway, where the major portion of the electricity is produced from renewable resources. The highest emissions are forty times higher than the lowest emissions, so the heat pump can be named a "green" heat source only in those countries where electrical energy is produced from hydropower or nuclear power plants. The methodology to calculate the critical value of the average generation factor for power plants, from which the heat pump causes lower carbon dioxide emissions, was developed. As an example, the calculations were performed for the ground heat pump, gas condensing boiler, and the oil boiler. In conclusion, for the countries where solid fuel is major source of electricity, heat pumps should not be applied. Instead, condensing gas boilers should be used. (C) 2013 Elsevier B.V. All rights reserved.