Only obvious if you know what a heat pump is!
Plenty of people will hear "Electrical heating is 100% efficient" and interpret that to mean it's the ideal solution, when in a lot of cases it's just about the worst.
But yes, if you have electrical heating, you could throw in some CPUs or ASICs instead and they'll work just as well. The return on investment for cryptocurrency may drop off a cliff when the next silicon process comes out and mines more for the same energy, it's hard to see people wanting to keep upgrading their baseboard heaters on the same cycle that computers get replaced.
Whether it's money positive vs resistive heating will depend on A) price of your electronics relative to a cheap electric heater, B) how it stacks up vs future electronics if the payoff doesn't happen while it's new, and C) how insane the cryptocurrency markets get.
Strictly speaking, isn't it just a special case of resistive heating?
Remember, few things need constant heat output 24/7 365, otherwise your going to want to generate some or all of your heat from other sources.
Aka, you can uses them to cook with. Also, while you can use electricity to heat water it's vastly more efficient to burn natural gas to make heat than burn natural gas to make electricity to make it, ditto solar power etc.
They cost more money, but Consumer Reports says "payback time is short" (see https://www.consumerreports.org/cro/water-heaters/buying-gui... ).
They probably don't make as much sense in cold climates, but where I live, air conditioning in the summer (and spring and fall) dwarfs the energy usage from heating in the winter. So a device that makes it colder on average indoors would be a net win even if it didn't have the function of heating your water.
Has anyone had 7+ years experience with these, and if so, can you please share your ownership experience and the model & brand you used?
Is it useful? My (limited) understanding is that most of the work is just arbitrarily difficult number guessing for the sole purpose of being throttled...
Obviously heat pumps are more efficient - that's kinda beside the point though.
The main point here is you can take anywhere you had a resistive heating element and replace it with a mining chip, and you're now doing something useful with that energy you were turning into heat anyway.
Yes heat pumps are more efficient but there are plenty of places in your house you have plain old heat elements that aren't going away (water heater).