Heat pump water heaters are also bad, I wanted to buy one and didn't because they are very slow to heat the water. Too slow to be useful for me.
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.
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.
A 40 gallon tank can provide 2 showers per hour. You can get 80 gallon ones for residential use, larger than that is in commercial territory.
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.
Congratulations on creating a scenario in your mind that will never happen. If you are all less than an hour away from leaving for an event, why are you washing clothes that won't be ready in time? Did you really have to run the dishwasher right before Kim's wedding or could you have set it to run while you are gone or after you get back if you somehow have a dishwasher without a timer setting? If you know you need four people to shower, maybe don't all wait until the last minute.
Is this a theoretical analysis? My assessment is that they are already much better, particularly if combined with an efficient house and sufficient battery storage to use low demand electricity. The power output from an ASHP can exceed a typical gas boiler if that is desired.
Our heat-pump water heater is outdoors, so it doesn't cool the house down any further. Our hot water cylinder is also able to heat water if the heat pump can't keep up.
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.