It depends on what you mean by "cold weather", but modern air source heat pumps are getting increasingly efficient in surprisingly cold temperatures. This Sams

It depends on what you mean by "cold weather", but modern air source heat pumps are getting increasingly efficient in surprisingly cold temperatures. This Samsung model I randomly found from a Consumer Reports link (https://ashp.neep.org/#!/product/65014/7/25000///0 https://ashp.neep.org/#!/product/65014/7/25000///0) claims to still heat almost as effectively well below freezing as it does at more mild winter temperatures. Even for less effective heat pumps, gas backup isn't really a requirement since you can often use electric "heat strip" backup like my home does. Heat strips are not particularly energy efficient, but many places that can get cold during the winter aren't continuously cold, so a less efficient electric backup is just fine.