Oxford study proves heat pumps triumph over fossil fuels in the cold::Published Monday in the scientific journal Joule, the research found that heat pumps are two to three times more efficient than their oil and gas counterparts, specifically in temperatures ranging from 10 C to -20 C.
This is the correct take for a conventional heat pump. However, there are relatively new geothermal heat pumps that can heat down to -30°C (-22°F) and are much more efficient.
https://www.cbc.ca/news/science/heat-pump-faq-1.6824634