The European Standard EN 50465 specifies the requirements and test methods for the construction, safety, fitness of purpose, rational use of energy and marking of a micro combined heat and power appliance (mCHP appliances). In comparison to the first edition, this second edition has been mainly revised in the following points: inclusion of requirements for Stirling engine and internal-combustion engine; revision of the requirements for fuel-cell heating appliances, consideration of experiences; partly adaption to EN 15502-1 and EN 15502-2-1, especially to reflect the new requirements for air proving devices; introduction of additional types of combustion air and flue duct systems; modification of the total efficiency calculation; modifications of NOx weighting and calculation. Since the new scope also comprises other fuel-cell technologies, the extended title of the standard reads "Combined heat and power appliance" (before: "Fuel cell gas heating appliances"). Micro-cogeneration (mCHP) is an efficient technology for heating, cooling and electricity. It is based on the simultaneous generation and utilization of electrical and thermal energy where the alignment of the systems with the heat demand of the application is considered as the most fundamental principle. mCHP appliances that are already established in the market are used to provide central heating and domestic hot water in residential buildings. A fuel cell, Stirling engine and internal-combustion engine are just some of the significant technologies to be thermal heart of a mCHP appliance. Other technologies are principally not excluded. Matters related to quality assurance systems, testing during production and certificates of conformity of auxiliary devices are still not dealt with in this European Standard. In detail, the following limitations apply to the scope: mCHP appliances of the types B22, B23, B32, B33, B52, B53, C1, C3, C42, C43, C52, C53, C62, C63, C82 and C83 based on the classification of CEN/TR 1749 that use one or more suppplied gases of three gas families at the pressures stated in EN 437, where the temperature of the heat transfer fluid of the heating system (heating water circuit) does not exceed 105 °C during normal operation and where the maximum operating pressure in the heating-water circuit does not exceed 6 bar and in the domestic hot-water circuit (if installed) does not exceed 10 bar, appliances which are either intended to be installed indoors or outdoors in apartially protected place and which are intended to produce hot water either by instantaneous or storage principle, which have a maximum heat input (based on net calorific value) not exceeding 70 kW and which are designed for sealed or open water systems. EN 50465 does not contain the requirements necessary for appliances capable of producing electrical energy without using the thermal energy. This standard does not cover all requirements for mCHP appliances that are intended to be connected to gas grids where the quality of the distributed gas is likely to vary to a large extent over the lifetime of the appliance (see Annex DD). The responsible body is DKE/K 384 "Brennstoffzellen" ("Fuel cells") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.