alt Hacker Newswell, in case of water heater it moves it from your room to the water.
Which means in winter that is extra work for your heating system to compensate for
But in climates where heating only really runs in winter it's great
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Technically your refrigerator heats up your kitchen in the same fashion adding extra work for your AC to compensate.
Unless you live in the artic where it's freezing year round, these things make sense. During the summer they reduce your cooling load and during the winter they are effectively heated by whatever your home heater is. Meaning if it's gas, then they are gas powered. If you have a heat pump outside then it's still pretty efficient. Even in the worst case of a resistive heater you are basically just running a slow resistive heater.
The one mentioned in the article has an outside unit.
And for the normal ones, at least they are leveraging outside temperature parts of the time while everything else stays at 1 in 1 out.
The ones in Japan go outdoors.
Most homes in Japan for decades have been designed for Tankless Gas Water Heaters stuck on the side of the building so there is no room indoors for a water tank.
The condenser unit for this literally just looks like the same one as for a regular mini split air conditioner, just a little bit larger.
This specific model appears to be a split system that has an external unit to extract the heat from the outside air.
which is why the bit thats sourcing the heat/cold is outside your house. it either has a massive radioator and fan, or pipes undergorund to source/sink the heat
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Technology Connections has recently published an in-depth piece of the advantages and disadvantages of in-room heat-pump water heaters [1].
The tl;dw is that it is significantly slower than a resistive or gas-powered water heater, and lowers the temperature of the room by a few degrees, but nothing major. You have to over-provision them compared to your needs. And they are way bigger.
These tend to work fine down to -25° C or so ambient temperature (you lose some efficiency below -5° C or so), so should always be outside. Obviously you need an alternate source of water heating if you live somewhere where it routinely gets below that, but even in a lot of places like that you could set it up to use the heat pump 90-95% of the year and a cheap but far less efficient resistive heater for the very cold days, and still come out far ahead.