In order to optimize the combined heat and power (KWK) in the whole operating range of an electricity-heat generation plant, the operating parameter of a unit combined heat and powerplant in connection with a compression heat pump for meeting the additional demand of heating power through the recovery of environmental hear or process waste heat are investigated The proportion of the electric to the thermal efficiency is used as a decisive characteristic number for the combined heat and power in the individual case of operation. The total operating number, which refers to the design efficiency is in dependence on the relative electricity characteristic number compared with those of the unit combined hear and power plant with heating boiler and the combined heat and power plant-with back pressure-steam bleeding. The cost-effectiveness of a hear pump-unit combined hear and power plant is compared with the cost-effectiveness of a unit combined heat and power plant with heating boiler on the basis of the annuity factors and the return flow period of the invested start capital resulting from this.