532
Heat pumps can't take the cold? Nordics debunk the myth
(techxplore.com)
This is a most excellent place for technology news and articles.
Second the NEEP database. I'd just add that the lowest temps listed here aren't the actual equipment minimums - each model has a cutoff temp where it will literally shit the bed (except ground source of course). For my mistu hyper heat, it's -26F. Capacity will keep dropping after -13F though (where it's still at like 80% I think).