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Definitely works in cold areas. Most heat pump manufacturers offer separate models for cold climates below zero.

The worst case is efficiency approaches resistance heating at 1.0, maybe with backup resistance heat strips. But a well designed system to match worst case load should rarely see this.

For some reason they've really only been widely available in the US in the past few years.

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> But a well designed system to match worst case load should rarely see this.

Well actually it'll see it quite often. Every time a heat pump goes into defrost mode it'll use resistive heating inside to hold over while it's working like a traditional air conditioner to thaw out the outdoor coils.

> For some reason they've really only been widely available in the US in the past few years.

I think it's cheap energy. In places like Japan they've been using heat pumps a long time

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