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Heat pumps sold so fast in Maine, the state just upped its target
(www.canarymedia.com)
This is a most excellent place for technology news and articles.
In Scandinavia we run ours down to -4F or colder. Efficiency goes down but they are still better than 1:1 until then.
Average temperatures for Bangor, Maine in January are colder than the average temperatures for January in Stockholm, Sweden.
Bangor
Stockholm
Still within range of a good heat pump but Scandinavian countries don't have a lock on cold. January averages where I live in the US are colder than Reykjavik, Iceland!
Well.... Iceland has ocean warmth due to gulf stream and is a literal vulcanic Island. Heck Island doesn't have heating problems, they just capture heat from the hot springs created by the vulcanism.
As such Iceland is kinda misleading as is Greenland. Iceland has less ice than greenland. Though Iceland is not green, more like black given all the volcanic basalt.
Average January temps where I live are lower than Stockholm. I chose Reykjavik because it's a neat place, not because it was particularly cold. :)