Primary energy factor (Primärenergiefaktor)

Definition

The primary energy factor (Primärenergiefaktor), abbreviated fp, is a dimensionless metric that maps the energy effort from the raw material (extraction, transport, conversion, distribution) through to delivery as usable final energy in the building. It is anchored in the German Building Energy Act (GEG, Gebäudeenergiegesetz) and the Energy Performance Certificate (Energieausweis) and serves as the basis for assessing the climate impact of different energy carriers. Typical values are: natural gas and heating oil each fp = 1.1; wood pellets fp = 0.2 (very low because of the renewable raw material); electricity for heat pump operation fp = 1.8 (as of 2026); district heating variable depending on the generation mix (combined heat and power, fossil, renewable). The lower the primary energy factor, the more efficiently the energy carrier is rated in economic and ecological terms. The factor feeds directly into the calculation of a building's primary energy demand, which in turn defines the Effizienzhaus classes in the Energy Performance Certificate and in KfW funding.

When is the term used?

The primary energy factor is central to every Energy Performance Certificate (Energieausweis) and to KfW funding assessments. It determines whether a building meets the requirements of a given Effizienzhaus class. The factor becomes particularly important when choosing the heating system: heat pumps benefit disproportionately from the legally set reduction of the electricity primary energy factor, which continues to improve as the share of renewable energy in the grid mix grows. The fp also plays a decisive role in the crediting of self-consumed PV electricity or district heating.

Example