Heat pumps sold in Norway are claimed to work down to -30°C. See, for instance, the Samsung Nordic Extreme: https://www.elkjop.no/product/hjem-rengjoring-og-kj

Heat pumps sold in Norway are claimed to work down to -30°C. See, for instance, the Samsung Nordic Extreme: https://www.elkjop.no/product/hjem-rengjoring-og-kjokkenutstyr/inneklima-og-varme/oppvarming/varmepumpe/samsung-nordic-extreme-09-varmepumpe-ar09bxfydwkee/522095?service=INSTHEATPUMPB#specifications https://www.elkjop.no/product/hjem-rengjoring-og-kjokkenutst... I don't know what the coefficient of performance is at that temperature though.