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Comment by willvarfar | Hacker News Reader

Outside temperature definitely affects an air heat-pump's performance, but the ones common in sweden stop being effective at -10c or even -15c.

I have a ground-source pump and its brilliant. But plenty of my neighbours are happy enough with air-source pumps.

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Recent conversations with net-zero builders indicate that ground-source pumps are being pushed away for most single-family residential projects in favor of the new-generation, highly-effective, cold-climate air-source heat pumps.

Mitsubishi and Fujitsu seem to have a large lead in cold-climate air-source heat pumps that are rated effective to -13F (anecdotal reports greenbuildingadvisor.com indicating effectiveness down to -20F). Yet, talking to builders, contractors, friends, and family, you will often still hear old tales about how "heat pumps aren't effective below 40F". Heat pumps come in a wide range of flavors. It's clearly possible to heat your house exclusively using an air-source heat pump in most USA climates.

There's a huge difference between air-source heat pumps and rebranded AC units running in reverse. We have a Mitsubishi FH35 6kw heat pump that easily heats 80 m2 (800 sq feet) down to -13 C this winter.

Do you recommend the model you quoted in your comment?

I do, it's fantastic! Just make sure to get a good installer for it.

As a fellow northern climate person, now in Arizona, have you any idea its efficacy in the 45 celsius normal summer heat, for cooling?

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