Why would anyone need a heat pump in California, given the climate there? I can understand north-eastern states, but not this. Is it a case of mindlessly jumping on "progressive" bandwagon?
EDIT: I actually spent one winter in San Diego, and apartments there don't even have any heating installed (except occasional fireplace in the living room). I know that more to the north it might get worse, but by how much?
Ever wonder why it’s called a “heat pump” rather than a heater? It’s because they work in both directions, and that means that you can have the system which keeps you cool in the summer also keep you warm in the winter rather than having a separate system. This is especially nice because if you don’t use a heater much, you don’t know that it’ll work when you need it: where I lived in San Diego, the condo complex had radiant heat in the floor in every unit but once in a decade a cold snap meant people really needed it … and some of my neighbors learned theirs no longer worked.
The efficiency wins from a better quality system are nice, too. I live on the east coast now and went all electric a few years back. Our energy costs in the winter went up modestly - not much because heat pumps are great on all of the not incredibly cold winter days we get in the mid-Atlantic - but the savings in the summer versus the cheap AC the previous owner had purchased were substantial. The savings up front for a less efficient unit get eaten up pretty quickly if you use it regularly.
Everything was built in the 40’s-60’s and the average amount of insulation is 0. I live in the mildest part of CA, the San Francisco Bay Area. Today the overnight lows were in the mid 30’s and the high will be about 50. Without heating my indoor temperature would be around 50 which I find unacceptable.
I’m not sure what your bogeyman “progressive” bandwagon has to do with not wanting to live in 50° living spaces?
Heat pumps make lots of sense in California. It gets hot enough to want air conditioning and still gets cold enough to need heat in much of California. California has many types of climates. Even in the desert areas like near Joshua Tree, you will still need heat in the winter. It snows there.
I live in one of the mildest parts of California and I still have a gas furnace (no AC though). Heat pump actually makes more sense given that the winters rarely dip below freezing, so heat pumps can work in a fairly high COP range.
I used to own a house in Claremont, California (east edge of L.A. County). It had a furnace that I never used until one winter it got super cold (under freezing as I recall) and I discovered that the pilot light for the furnace was broken and had to call out the gas company¹ to fix it and because everyone else was having similar issues it took two days for them to come and fix my furnace. I grew up in Chicago and was never so cold as that.
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1. They fixed minor furnace issues like this for free.
For the same reason people in California install heat and air conditioning? Heat pumps aren't a new product market, they're a more efficient variant of products the market already buys.
I live in San Diego and energy prices are relatively expensive. We installed solar two years ago and routinely overproduce 3+ MWh.
Now, with a heat pump, the wife and kids can set the thermostat for their comfort and I am less anxious about the monthly bill. The freedom was worth it, for us.
Heat pumps are much more common in warm areas than cold ones, because the difference between an A/C and a heat pump is really just the ability to reverse the refrigerant flow, and they're very efficient at heating in mildly cold weather. I grew up in Florida, and pretty much every house there had a heat pump even thirty years ago, with electric resistive heating that kicks in when ambient temperatures drop below 40F or so. Where heat pumps don't work so well is when ambient temperatures are very cold, which is why adoption in northern states has been much slower.
EDIT: My grandparents' house had a thermostat that looked like this: https://i.ebayimg.com/images/g/uqsAAOSwTVlbyNN9/s-l1200.jpg They would call very cold (for Florida) weather "blue light weather", because the blue "aux heat" light would turn on on their thermostat, indicating that the system had switched from the heat pump to the resistive heat strips.
My sister just got a heat pump installed in her new house in Poland, where temperatures occasionally drop to 0 Fahrenheit. I wouldn't say they only work in "mildly cold weather" - as per new EU policy heat pumps will be one of the few legal heat sources, even in countries such as Sweden.
Modern heat pumps can work in very cold weather, but they're much less efficient, which is reflected in their COP numbers. In my house in Chicago, we have a hybrid system--the heat pump works down to 20F or so, and we have a natural gas furnace for colder times. Natural gas is very cheap here, so this is the most cost-effective solution at the moment. I'm very eager to electrify and remove my dependence on natural gas, but I think it will be at least a few more years unless there's some breakthrough in cold-weather heat pump efficiency, or an enduring spike in natural gas prices--last time I did the math, the breakeven point for electrification here is around a COP of 4, which no heat pump can do at typical Chicago winter temperatures.
If I were building a brand new house, I probably would do it 100% electric. But most people here already have natural gas furnaces, and when they reach end-of-life they're usually replaced with another natural gas furnace. Hybrid systems like mine are catching on, but it will be a while before 100% electric is commonplace here.
I consider a winter where the coldest it gets is 0F a mild winter. The important thing isn't average or normal it is the worst case. I've personally seen -25F here in the last 10 years - it was only one time and lasted about a week, but that means the HVAC system needs to work down to at least -25F just in case.
I don't know what the climate is like in Poland. Maybe 0F is as cold as you ever get and you are okay. Maybe your system will work to -20F even though you haven't tested it. But your might have a system like mine that while it can deliver heat at 0F, it is sized such that below 30F it can't deliver enough heat (I have the backup system for those colder days)
EDIT: I actually spent one winter in San Diego, and apartments there don't even have any heating installed (except occasional fireplace in the living room). I know that more to the north it might get worse, but by how much?