Does a heat pump really work in winter?

“Yes. Modern air-to-water heat pumps (Daikin Altherma 4 H, Vaillant aroTHERM plus, Stiebel Eltron WPL-A, Panasonic Aquarea T-CAP, Alpha Innotec hybrox, Buderus Logatherm WLW176i) operate down to -20 °C with a reduced COP. Geothermal is never affected by outdoor temperature since it draws from the stable-temperature ground. No electric backup is required for correctly sized installations.”