Heat pump water heaters and heat pump air heaters solve that problem and save money.
Heat pump dryers on the other hand are a bit rubbish (take a very long time to dry clothes, but they do save money).
They are especially bad in northern climates since the incoming water is cold, and they put cold air in your house - which then has to be heated by the home heater.
An A/C is already a heat pump.
it goes in an insulated tank? why does the speed matter? the tank is always at temperature. if you run out of hot water, that’s a tank size issue, not a heater technology issue.
But that's still just 4 showers - if you have a bunch of people all getting ready for an event, and you also have laundry to do (which uses double what a shower uses, although takes longer) and run the dishwasher, etc.
It's not enough. You would need a truly mammoth tank.
Instead you have a large fire at the bottom, and heat the water almost as fast as you use it, then you don't run out.
A heat pump water heater would simply not work for a 6 person home in the north in the winter.
That is desired, and apparently is not actually the case. I did my research and that's what people tell me, so I didn't get one.
They might work better in hotter climates, but in northern ones with incoming water near freezing, they don't.