The increased use of combined heat and powerplants, especially in the form of unit heal and power plants has been discussed adversely in public. The evaluation of such plants takes place on the basis of a comparison between different systems of the separated and combined generation of power and heat. The paper deals with the basic weak points of such comparisons. The importance of the combined hear and power generation is set within a new framework from the exergetic points of view. The considerations are illustrated on examples and are generalized with the help of parametric contemplations.