Mine can go until -25c they say: https://www.nibe.eu/en-eu/products/heat-pumps/air-water-heat...

We don't ever get those temps so I should be fine.

My biggest issue is not cold but mist. I live near a river in a valley and have underestimated how much mist hurts performance around ~1c outside.

It needs to defrost often, because of the high moisture content in the outside air where I live.

But it also has a normal, resistive heating 9kW backup. But for financial reasons this is considered 'emergency only'.