A heat pump in a typical single family home uses 3,500 to 5,000 kWh of electricity a year. (Sentence with source 1) With a heat pump tariff of around 28 cents per kWh that is about €980 to €1,400 a year. (Sentence with source 2)

Older houses without floor heating sit at the upper end, because the pump has to heat the water more. (Sentence with source 1, 3) Your quote assumes 4,200 kWh a year. (Sentence with source 4) The exact value depends on the winter and on how much hot water you use.