AC (and heat pumps in general) is great for heating, it can be way more power efficient than anything else. I mean, in theory, its efficiency can be way higher

AC (and heat pumps in general) is great for heating, it can be way more power efficient than anything else. I mean, in theory, its efficiency can be way higher than 100%. But that's only when it's not too cold outside (I guess, at least above zero). You can consider using it in spring & autumn periods.