Abstract: An air-conditioning apparatus forms a refrigerating cycle with a refrigerant heater and a compressor having two cylinders. The apparatus simultaneously carries out a refrigerant heating operation and a heat pump operation when a required heating capacity is high, and when the required heating capacity is low, only the heat pump operation. This operation technique helps reduce the size of the apparatus and expand a variable width of heating capacity. The apparatus also has a defrosting unit for defrosting an outdoor heat exchanger during the heat pump operation.

Abstract: An outdoor unit comprises a combustion unit for presenting combustion heat, a heating medium heating part for heating the heating medium with the combustion heat to vary in phase from liquid to gas, and a heating medium transferring part. A plurality of indoor units each have an indoor heat exchanger and a required heating capacity detecting part for detecting a required heating capacity in a region to be heated required for the indoor heat exchanger. The detecting part comprises a room temperature setting part, a room temperature detector, and a required heating capacity data output part for delivering required heating capacity data in the region to be heated depending on the difference between the preset room temperature and the detected room temperature. The distributing part couples the plural indoor units parallel to the outdoor unit so as to form individual enclosed heating medium circulation cycles.