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Comment by User23 | Hacker News Reader

I’m not fan of a heating technology that only fails when I need it most. The system can work adequately thousands of times, but I only get to freeze to death once.

Winter Storm Elliott dropped temperatures far below the average lows in places that might otherwise be well served by heat pumps. Many southern states saw -5 F and it got considerably colder elsewhere.

That’s not to say that heat pumps can’t play a role in HVAC systems, but they must have a backup.

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Heat pumps are specified with significant margin and/or backup heat sources.

The numbers above are the 1:1 point, which doesn’t mean it stops working. It just means it’s similar efficiency to an electric heater at that point.

“Freeze to death” is an extreme exaggeration.

This is spot on. Some mini split heat pumps effectively become base board heaters with a fan when their efficiency falls off. You'll be uncomfortable, but you won't freeze to death.

You always need a backup heat source in cold climates. Even if you have typical heating like baseboards of central gas furnace, they can and do fail and for that reason you need backup. Heat pumps are no different, but their efficiency drop off isn't a "failure", it's just a limitation. Being a predictable limitation you can plan for it, and be sure your backup source does not rely on electricity because that always goes out in a storm.

It's not that the heat pump fails when it's < 20C, it's just that you don't get any additional efficiency versus heating directly with electricity.

I have a heat pump and I live in Canada where it’s not uncommon to see -40 degree temperatures in winter. The system has a high efficiency gas furnace as the backup (auxiliary) heat source. So far this winter the heat pump has been doing the bulk of the work. Only when the temperature starts to drop and the heat pump can’t keep up does the gas furnace kick in. The system works pretty well.

I just wish the thermostat let me customize the threshold a bit. I don’t like having the heat pump go to maximum load before it lets the furnace come on. Ideally the system would know the current prices of both gas and electricity and run whatever is cheaper, given the indoor and outdoor temperatures.

It'll still work somewhat. Just inefficiently.

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