The annual efficiency coefficient is not significantly affected by the heat pump efficiency data at extremely low temperatures. In our climate zone, extreme cold temperatures are rare and, if they do occur, they last for a very short time relative to the heating season. For example, the temperature may drop to -20 °C at night but rise to -14 °C in the morning.

The important thing is to have an additional heat source (in most cases an electric heater) that can sufficiently cover the additional losses of the building in such extremely low temperatures.