This paper analyses practical procedures for the virtual recognition of CHP (Combined Heat and Power) and non-CHP parts of the plant, and for determining their efficiencies and other parameters required by the regulator. The division of the plant into CHP and non-CHP parts is done on the basis of standard measurements carried out in practice, and the correct thermodynamic energy balance. The Energy efficiency of the CHP part is equal to a pre-set value and that of the non-CHP part is lower than this value. Instead of the Primary Energy Saving (PES) indicator, which compares the efficiency of a CHP plant with a classical plant for the production of heat energy and electricity, here we are analyzing a method that recognizes only the part of the CHP plant that fulfills the preset value of high-efficiency cogeneration. This value is prescribed by the national regulator and depends on the type and age of the plant, operating conditions, etc. Practical calculation procedures rely primarily on rules that are used in the EU (European Union). The impact of a changeable practical operating mode and the sensitivity of the referred efficiency to the attractiveness of cogeneration is particularly evaluated. (C) 2017 Elsevier Ltd. All rights reserved.