Abstract
In connection with the implementation of the energetic certification law in the European Union the issues relating to an air-to-water heat pump performance in a monovalent system in European climatic conditions have been discussed in this article. Running costs for an air-to-water heat pump-based system and conventional systems have been estimated. Analysis based on the law and concerned mono mode operation of a heat pump has been carried out for a classic single family house that has been built according to the standards and regulations valid in Poland.