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Comment by jgalt212 | Hacker News Reader

> Something like 70% of houses are heated by heat-pumps

To me, living in US Northeast, this is astounding. I've read heat pumps lose efficacy below 25F. My family would never forgive me if I made our house cold. But then I see 70% of the Nordics's house are "warm enough", or dealing colder than room temperature houses.

I've asked half-dozen contractors and HVAC people in my area, and none of them have recommended a heat pump. But, I'm just as suspicious of their motives as I am of the science and environmental populizers on YouTube.

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That's old heat pumps. Mitsubishi introduced their "Hyper-Heating Inverter" heat pumps designed to work well in cold weather in 2007, with Fujitsu and Daikin adopting similar technology by 2012, and others following within a few years.

These remain 200% efficient down to -4℉ and 150% efficient down to -22℉. Their capacity starts dropping at 23℉ going down to 76% capacity at -13℉.

There's only a few towns in the continental US that cold enough for long enough that it can't be heated well by one of these. You just need an installer that will size it properly for the climate in your area.

Don’t let the 15 degree+ differences in latitudes fool you, a lot of the Nordic population lives near the sea, so low altitude and plenty of sea current temperature moderation.

January temps in Oslo aren’t much different than Boston. Absolute record low temps are similar too.

Coldest temp ever in Oslo is -30C in the 1800s.

Coldest in Boston was -28C in 1934.

Still doesn’t explain the poor adoption in USA but helps explain why they still work so far up north. The nordics can be relatively balmy to Wisconsin or upstate New York.

A lot of the Nordic heat pumps are ground source, that is to say you drill a hole a couple of hundred feet down into the bedrock where it's always a bit above freezing and you circulate your heat exchange fluid down there and back up again. Air-source heat pumps are mostly a thing in the southern parts where the climate is relatively mild.

Air-source heat pumps are also somewhat common in retrofits where the remaining expected lifetime of the building isn't big enough to be worth spending some 20-30k€ (?) that installing a ground source heat pump costs. A significant part of the cost being drilling the hole.

Similarly for small houses the cost of the hole drilling might not be worth the reduction in electricity consumption.

You never go below 1 in efficiency. Worst case the water is heated directly with electricity.

You shouldn’t but you could.

In theory peltier elements are more efficient heaters than resistive heating but if the temp delta are big enough, you lose more heat through conduction than you pump in.

A poorly optimized fireplace may vacuum more warm air out than it radiates in.

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