This standard provides a calculation method for the economic issues of heating systems and other systems that are involved in the energy demand and consumption of the building. It applies to all types of new and existing buildings. The fundamental principles and terminology are explained in the standard. The main items of the standard will be: - the definitions and the structure of the types of costs which shall be taken into account for the calculation of the economic efficiency of saving options in buildings; - data needed for definition of costs related to systems under consideration; - the calculation method(s); - expression of the result of the economic study. This standard is part of the method for calculation of economic performance of energy saving options in buildings (e.g. insulation, better performing generators and distribution systems, efficient lighting, renewable sources, combined heat and power& ). The scope of this specific part is to standardise: - the required inputs; - the required outputs; - the calculation formulas; - The type of energy systems concerned with the energy performance of the building. NOTE This is the revision of EN 15459:2009. The revision has been made consistent with the EU regulation on cost-optimal. This revision includes the definition of payback for investment, and inclusion of the costs due to the deconstruction of the building. The method presenting annualised costs has been suppressed.