Fortunately for this particular case, Berkeley winter temperature hasn't seen a record low below 25 degrees F in the last 30 years. Or more, Wikipedia doesn't g

Fortunately for this particular case, Berkeley winter temperature hasn't seen a record low below 25 degrees F in the last 30 years. Or more, Wikipedia doesn't go back further than that. https://en.wikipedia.org/wiki/Berkeley,_California#Climate https://en.wikipedia.org/wiki/Berkeley,_California#Climate So heat pumps should be OK for Berkeley.