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Comment by tejohnso | Hacker News Reader

Can you explain why it is extremely rare if we should be using it? Is it politics? Branding?

There's a lot of inertia against heat pumps for reasons that are not at all clear. Where I live, in a pretty northern climate where until recently almost no one owned an AC but climate change is very visibly changing that, it's very difficult to get HVAC people to take you seriously if you say you want a heat pump even if you're getting an AC anyways.

A lot of it seems to stem from the fact that most heat pumps operate poorly or inefficiently below about -10C (some higher than that). The fallacy that lies behind the inertia seems to be that "if you can't use it exclusively, you shouldn't bother at all". Since there's a non-trivial number of days below -10C where I live (about 1078 hours spread across 89 days here last year), it's considered frivolous.

Of course, because we build our houses to hold in as much heat as possible for winter, now that it's getting over 20 and 30 a lot more a lot more people are buying AC, which is all of a heat pump other than a reversing valve, so to me it seems silly to NOT get a heat pump for the like 200+ days in between peak heat and peak cool seasons.

The reason heat pumps have traditionally been untenable is that they are prone to icing over when below freezing. If the coils are covered in ice, then air can't be blown past them to get new heat to pull in.

Further, in many cases, the heat pump wouldn't keep your house warm during the coldest period of the year, which meant you still needed a heater. Not a huge deal since you probably have an AC for the summer anyway.

The issue as I understand it, was that the thermostats were not smart enough to know when to quit and so a heat pump would run until it literally could not keep up with demand, when it should have instead switched over to gas heat some time earlier than that when efficiency dropped.

Modern heat pumps deal with all these factors to the point that I expect them to become standard fare as current ACs get upgraded over the next decade or two. I know that if we ever need to upgrade our AC it will be replaced with a heat pump.

Yes, these are all definitely issues. None of them should have been difficult to solve a long time ago though, there was just a lot of inertia behind it.

And there still is. Even now I'm talking to an hvac guy who seems generally knowledgeable and even he said something to the effect that "there isn't any heat in the air below -10" which is just not true at all. It's less efficient to pull it out for sure, but there's always energy to suck out of air.

Anyways, like I said, even up here where people barely know heat pumps exist there's still over 200 days of the year where even a shitty heat pump would do a decent job. Still people argue it won't get used.

(all of this is ignoring the fact that we should be doing even moderately expensive things to get off using natural gas if we can)

I think it's cost, especially in an area where A/C isn't needed (or at least, hasn't been needed in the past).

I live in the Pacific Northwest and when I wanted to swap out my furnace for a heat pump, a few vendors aid that they don't install heat pumps, they could do a furnace or A/C, but not a heat pump. I have no idea why that is, I figured that heat pump installation is nearly identical to A/C. (I still use a furnace for emergency heat as I wanted to be able to run from a small generator if needed)

The heat pump + furnace replacement cost 2 - 3X more than just a simple replacement furnace, so I can see why someone wouldn't want to spend the money if they didn't need A/C.

Cost probably explains a good chunk of it. Regardless of why it's more expensive. When our house was built in 2012, I looked into getting a heat pump. But it was a couple grand more than a high efficiency furnace with an air conditioner. Given that natural gas remains inexpensive compared to electricity, it wasn't an obvious win financially. And if we're being honest, for average people the hit to the pocketbook is going to take higher priority than considerations for the environment.

They don't work below a certain temperature because condensation collects on the cool side, creating frost, and makes them less efficient than baseboard radiative heat. The lower boundary is about -10c. Not to mention gas is just way cheaper than both of those options. But it does emit greenhouse gas. I don't know why this topic comes up so much recently. It's just not common at all where I am for a reason (Canada).

I believe heat pumps for heating tend to not work very well when the temperatures drop too low. (At least in the RV versions I've seen. Once the temp gets below freezing, you have to use the onboard propane heaters)

There are modern, “hyper heat” models that can heat at 90% of rated output down to -13°F.

That might still not be enough if the local 1% design temp is +5°F and, as a result, your unit is sized to maintain temp at +5°F, so doesn’t keep up for the 88-ish hours per year that your temps are below the design temp.

Northeast has expensive electricity as well as the other reasons stated.

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