In modern, well-insulated buildings, more energy leaves the building with the warm wastewater than is needed for heating. Most of this energy is contained in the greywater. If a greywater recycling system is installed in a building anyway, it makes sense to extract this energy from the treated greywater shortly after the point of origin via a heat exchanger using a heat pump and to feed it back into the hot water system. With early planning, heat pumps can be used to which this additional heat source can be connected. This results in the lowest additional costs. The heat recovery from the gray water can be up to 15 kWh/m³ (assumption: 25° inlet - 10° drawdown, ca. 1 kWh/°/m³). At energy prices of 30 cents/kWh, this would correspond to a saving of 4,50 € /m³ grey water.
