This is because at low outdoor temperatures, depending on the design and operation of the heat pump, an electric backup heater may switch on, which requires additional electricity and can therefore increase electricity costs. Especially since an increasingly electricity-based heat transition requires a further expansion of electricity generation from renewable energy sources.

When temperatures are mild, things look different again. In the summer months, where almost only hot water is needed, and in the transitional phases of fall / spring, the heat pump can largely cover the heat supply. While, for example, in winter a water-bearing stove and/or a solar system can cover part of the heat and hot water demand. In addition, the heating system is relieved, which can reduce the operating time of the heat pump. When the fireplace burns, it not only provides a pleasant and cozy ambience, but part of the heat generated can be transferred into the heating circuit. Excess heat can be temporarily stored in a buffer tank in the form of hot water and is available for retrieval even after the fire has gone out.

Of course, a hand-operated stove can also provide pleasant warmth in the installation room with its blazing fire. Then the heating demand to be covered by the heat pump can be reduced and the operator controls its demand manually. The solar system can also provide support, for example by contributing to the hot water supply.