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Transcripción del abstract original del autor: This paper introduces the development of compact high-capacity (hot water output: 42 kW) residential condensing boilers for Gas central heating. A large share of the residential and commercial markets for water heaters in Japan has always been taken by instantaneous gas water heaters due to their performance and installation advantages. Electronic control has brought additional functionality, more functions, and higher safety levels to them. On the other hand, though basic research into the use of condensing boiler technology to improve the thermal efficiency of appliances has been in progress, that has never reached the stage of being incorporated into products and marketed. As a result, the efficiency of such water heaters has not increased from its maximum of about 80%(HHV) for more than 20 years. Recently, attempts to save energy as a global warming countermeasure have been progressing in all fields, and there is a strong demand for further efficiency improvements in residential water heating appliances, too. There has also been increased competition from other energies in the residential water heating sector, particularly with the launch of a new electric heat pump water heater which uses CO2 refrigerant in 2001. This competition is being countered with a rapid expansion of the lineup of high-efficiency gas water heaters. This is the situation that has led to the commencement of commercial development of residential condensing boilers for gas central heating.