Induction Water Heaters: Are They Worth It?

[BWV]

Was curious if induction water heaters were a thing and if they had any benefits over a traditional electric resistance coil. On quora someone argues that a resistance coil is a near perfect conversion of electricity to heat, therefore no benefit to induction - is this correct? Is the efficiency gains in induction cooktops solely due a more to less waste heat between the coil and pan than with a resistance coil? But then if induction transfers heat more efficiently to the metal surface on a cooktop, why not in a water heater?

 

[DaveE]

In almost every water heater I every knew about the heater coil is completely submerged in the water. There is nowhere for the heat to go except into the water. That isn't the same as a cooktop. I fail to see any advantage to the greater complexity of induction heating compared to a submerged resistive heater. Someone on quora was correct, resistors are the simplest, most efficient way to convert electricity to heat.

 

[Bystander]

Induction stoves/cooktops are safer as far as burning/cooking small children.

 

[BWV]

They boil water faster, have a small induction hot plate alongside my gas cooktop that I use for pasta

 

[BWV]

In almost every water heater I every knew about the heater coil is completely submerged in the water. There is nowhere for the heat to go except into the water. That isn't the same as a cooktop. I fail to see any advantage to the greater complexity of induction heating compared to a submerged resistive heater. Someone on quora was correct, resistors are the simplest, most efficient way to convert electricity to heat.

Makes sense, thanks

 

[zoki85]

A jet-type electrode boilers are probably the most efficient

 

[Baluncore]

Someone on quora was correct, resistors are the simplest, most efficient way to convert electricity to heat.

Resistive elements are simple, but not the most efficient.
A heat pump is more complex, but it is significantly more efficient than a resistive element.

 

[russ_watters]

Resistive elements are simple, but not the most efficient.
A heat pump is more complex, but it is significantly more efficient than a resistive element.

I don't think is pedantic in this case to point out that a heat pump does more than just "convert electricity to heat". As such it is not always interchangeable with devices that do just that. E.G., an electric resistance, induction and even a gas range are functionally equivalent, but there is no such thing as a heat pump range. Heat pump water heaters and "boilers" do exist, but have requirements/capabilities and limitations that do not constrain electric resistance or gas devices.

 

[Nik_2213]

Induction stoves/cooktops are safer as far as burning/cooking small children.

Unless you are wearing something that will 'respond' to induction field and carry eddy currents ??

 

[Baluncore]

... there is no such thing as a heat pump range ...

I did not think the kitchen range was an important consideration as the title of the thread was “Induction more efficient than resistance for a water heater?”
Heating water is one thing that a heat pump does with over-unity efficiency.

 

[russ_watters]

I did not think the kitchen range was an important consideration as the title of the thread was “Induction more efficient than resistance for a water heater?”

The OP asks specifically about the differences between ranges and water heaters that might make one work for a range and not a water heater. The opposite can be considered as well.

There is also overlap of course in that if you are using a range to boil water, you can do half of the heating with a water heater or all of the heating on the range.

But all that said, I've never seen a heat pump water heater in a residential setting and only once commercially*, so even then it isn't exactly equivalent to the others, which is why I pointed it out. One big potential downside is they need an external heat source. Heck, it is even common commercially for an a water to air heat pump to be sourced from an electric boiler!

*Er; the commercial one was hot water for heating, not drinking. Residentially, checking what I think are the top 2 manufacturers, both offer air source heat pump water heaters. In the summer they provide free air conditioning and in the winter their source is whatever you use to heat your house. That has to be considered in the analysis.

 

[DaveE]

Resistive elements are simple, but not the most efficient.
A heat pump is more complex, but it is significantly more efficient than a resistive element.

I guess your point is that heat pumps make better water heaters than resistive heaters. That certainly may be the case, depending on your requirements and the specs of each device (i.e. what sort of water heater you like).

However, I'll stand by my claim that resistors are the most efficient way to convert electricity to heat. In fact they are 100% efficient, the proof is so short it's essentially the definition of what a resistor is.

 

[Baluncore]

However, I'll stand by my claim that resistors are the most efficient way to convert electricity to heat. In fact they are 100% efficient, the proof is so short it's essentially the definition of what a resistor is.

You are ignoring the fact that a heat pump can be 200% efficient, when it requires only half the energy it pumps into the water.
https://en.wikipedia.org/wiki/Heat_pump

 

[DaveE]

You are ignoring the fact that a heat pump can be 200% efficient, when it requires only half the energy it pumps into the water.

Yes, exactly. I am talking about resistors. You are not.

You are talking about the "efficiency" of a more complex system. However, not a closed system, since "over-unity" efficiency doesn't exist for those. That sort of definition of efficiency makes more sense in the building trades than in a physics forum. After all, we are only paying for the electricity inputs, and we only care about the hot water that comes out. Why measure the stuff you don't care about.

 

[Baluncore]

However, I'll stand by my claim that resistors are the most efficient way to convert electricity to heat.

That is not physics. Electricity is not converted into energy. Electricity can be used to transfer energy from a generator to a load.

 

[Tom.G]

If using only electricity as an energy source, then of course a resistor is the most efficient.

However, if there is ambient energy available then a heat pump will have a higher electrical efficiency, but not a higher system efficiency. That 200% quoted above is obtained by dividing the output energy by the electrical input energy; the energy extracted from the ambient environment is ignored in that calculation. If you but put a closed box around the heat pump input stream, blocking the ambient energy, you get a refrigerator.

Additional note: Heat pumps used for residential living space in cooler climates are generally "Electrically Assisted Heat Pumps." This means there is a resistance heater that comes on when the outdoor temperature is so low that not enough thermal energy can be extracted from the ambient to satisfy the heating needs. The expensive units can operate down to ≈36°F, 2°C.

Here are a couple sites that may help:
An introductory article.
https://www.energy.gov/energysaver/water-heating/heat-pump-water-heaters

Experimental results of some installations.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770007641.pdf

(above found with:
https://www.google.com/search?&q=electric+assisted+heat+pump)

Cheers,
Tom

 

[sophiecentaur]

Unless you are wearing something that will 'respond' to induction field and carry eddy currents ??

Interesting idea.
Most jewellery is made of metals with high conductivity and such items are small, so the I²R heating would be small. I could imagine a 'retro' iron bangle could be a problem but even that would probably have too small an area to link to the induction field and would be too far away from the induction coil.

 

[artis]

@sophiecentaur well I think unless someone is a hardcore metal chain fan I think induction cooking is safe.

I totally get @Baluncore suggestion but a resistor still is the most efficient electrical device ever, it's just that a heat pump is an unfair player in this comparison due to the fact that it only uses input electricity to move a heat exchanger fluid/gas but doesn't produce it's own heat, and even if it did produce it's own heat it would lose to a simple resistor because an electric motor is not 100% efficient.
But if we simply compare two sorts of heating say a water boiler with a induction water heater , even though a boiler uses a resistor for heating which by itself is 100% efficient and the switching transistors and their drive circuits in the induction heater are not 100% efficient we must consider one additional issue. The induction heater is only working when water is needed, the boiler on the other hand is a reservoir and so keeps it's water at a certain temperature constantly, unlike a resistor, the efficiency of the boiler's heat insulation is not 100% so some heat continually escapes and this is why the boiler switches on after certain times to constantly reheat the water even if the water isn't used.

So I would say unless you constantly use the boiler the induction heater might get a lower bill even not being 100% efficient simply because it's only running when used instead of running constantly even for days when out of direct use.
I myself have a water boiler so i know this. In fact I am thinking about trying out an induction heater for comparison.

 

[Baluncore]

Real electrical power is the product of voltage and in-phase current. The ratio of voltage to current is defined as resistance. The power is; W =I²R.

The product of voltage and reactive current, VAR, is not real power or heat. An induction heater induces currents in a resistive material, that dissipates; W =I²R. The word inductance refers to the method of coupling, not to the element of heat production.

An induction heater requires high frequency AC be generated and delivered to the inductive primary winding element. Likewise, a resistor needs two conductors to guide the energy to the resistive element. Those conductors will also have I²R losses which reduce the system efficiency of the resistive element to below 100%.

As can be seen, it is an unfair comparison to consider only one component of a complex system, especially when by definition, that is resistance in both cases. For heating water, when the entire system is considered, a heat pump will outperform both the resistor and the more complex, less efficient HF induction heater.

Peltier thermoelectric coolers can be about 75% efficient, significantly less than a typical refrigerator. But a Peltier effect thermoelectric heater can be over 100% efficient and so might be considered as a possible replacement for a resistor when heating water.
https://scholarworks.uark.edu/cgi/viewcontent.cgi?article=1010&context=meeguht

 

[artis]

@Baluncore if I understand correctly these "Peltier" thermoelectric heat pumps basically get rid of the motor and fluid and all that and instead work on the principle of surrounding heat driving current through a junction , so basically you put some DC current through the junction from your power source and you get back that current plus additional electric current which is the result of the ambient heat energy converted to electricity?As for the wires going to the resistive heating element , given their good quality copper and sufficient AVG I'd say those losses are tiny, and every method will use wires , the induction heater as well as any heat pump.
I do realize the induction heater is so named because of the way the field interacts with the object to be heated which most likely will be a ferrous metal pipe so the water will be heated mostly through heat give off by the hot pipe.
I think that if one needs hot water quickly but not on a regular basis , the induction heating method would still be most economical simply due to being "on demand" while a boiler has to be kept on at all times, even if I don't use the hot water for a week.

Surely I agree that as far as electricity bill goes if one can simply scavenge energy/heat from the environment then the bill most likely will be lower.

PS. I do wonder how big the heatsink has to be even for the solid state heat pumps for given kw of energy provided, after all these are all costs of both manufacturing, transporting etc.

 

[DaveE]

I do wonder how big the heatsink has to be even for the solid state heat pumps for given kw of energy provided

Peltier devices are VERY non-linear in their thermal behavior. The amount of heat pumped is a strong function of the temperature difference between the hot and cold side. So the thermal design is important. For a heating application, if the cold side heat removal isn't appropriate then the large temperature difference will severely impact the heat pumping efficiency. However, in any case, it will still work like a resistor with the electrical power in making heat in the device.

For smaller high performance cooling designs (i.e. too expensive for the building trades), a good rule of thumb is that good designs will have the amount of heat pumped approximately equal to the power input, so for 1W of electricity in you will have about 1W of heat pumped from the cool side and 2W of heat dissipated at the hot side. However, there is a wide range of "optimal" designs depending on the system requirements. Commercial designs will drive the TEC harder to save money.

IMO opinion, initial cost and reliability considerations make solid state designs less attractive than mechanical designs assuming you can tolerate pumps, refrigerants, etc. After all, how many of your friends have solid state refrigerators in their kitchens?

For example, you can look at the TEC performance curves from the manufacturers, like the ones on this page:
https://www.marlow.com/resources/thermoelectric-technology-guide/iii-tec-selection-procedure

 

[sophiecentaur]

a resistor still is the most efficient electrical device eve

Agreed. However, the thread has started to discuss whole systems and, as tends to happen on PF, we've diverged and diverged. The only thing about a resistor is that you need to provide it with Electricity and that means that someone has to Generate it. A small, inefficient home generator and resistive heater would probably not give you a better performance than just burning the fuel in a hot water boiler.
Engineering is about systems and not components. But this is a fun topic to discuss and to bandy about various figures from the top of our heads.

 

[Baluncore]

The unconditional statement that “a resistor is 100% efficient and therefore cannot be beaten” restricts the consideration of more efficient engineering solutions.

I think I have made my point that “if you want to heat water, there are more efficient ways than using a simple resistor”.

 

[alan123hk]

Regarding the ways to make water boil, according to my personal experience, electric kettles have the highest efficiency, followed by induction cookers, and the least efficient are ceramic infrared cookers.

 

[artis]

I think @Baluncore that we could both agree that for someone who doesn't have a private house but instead lives in a crammed up highrise in his apartment in say the 9th floor his only real option are those that give power from a concentrated source and the only such real source I think is the wall socket, so here a resistor is still the king.
Now I know people use their AC units for heating in winters as an AC is essentially a heat pump, so for a highrise that's maybe the closest to a heat pump one can get.
But I doubt you would heat water with such a method.Well what I would like to know personally , with respect to the TEC Peltier devices, how much space they take up for given power? Because if what I know about the thermoelectric effect in general is true is that it doesn't have a particularly high energy density. I would love to hear comments on this.

 

[Baluncore]

I think Baluncore that we could both agree that for someone who doesn't have a private house but instead lives in a crammed up highrise in his apartment in say the 9th floor his only real option are those that give power from a concentrated source and the only such real source I think is the wall socket, so here a resistor is still the king.

I am sorry that you must live in such inconvenient accommodation, but it should not prevent creativity.

No doubt your neighbours use resistors to heat their apartment in winter. So why do you not install an equally spaced array of Peltier cells over a shared wall and pump heat from their apartment into yours? Put heatsinks with fins on your side of the Peltier elements. Insulate the rest of the wall with 3mm of foam or cork. I would call that active insulation, something you can't do with resistors.

 

[sophiecentaur]

I would call that active insulation, something you can't do with resistors.

Yeah. Engineering rules!

 

[artis]

@Baluncore well your suggestion is very interesting :D
I myself actually don't live in a highrise and not on 9th floor instead I live in a 4 story building and on the 2nd floor but still in a flat, as most such buildings around here we have centralized heating so there are no resistors involved, just hot water going through radiator pipes.

By the way I doubt you could get any good convection through a concrete or brick masonry wall.

 

[Baluncore]

just hot water going through radiator pipes.

How is that water heated? It seems like an ideal application for a heat pump.

By the way I doubt you could get any good convection through a concrete or brick masonry wall.

That is why the full area of the wall needs to be used, with insulation on the rest of the wall.

 

[artis]

the water is heated in a large 10MW central heating station run on recycled wood chips, basically due to EU regulations everything now here is run on either leftover wood chips or natural gas with few exceptions of coal and oil shale.

 

[sophiecentaur]

How is that water heated? It seems like an ideal application for a heat pump.

I was thinking about the mutual effect of a lot of air sourced heat pump installations operating in close proximity. There could be a 'battle' between systems for available Joules in the surrounding air. Otoh, the microclimate within cities tends to produce measurably higher air temperatures compared with those in the surrounding countryside. Wildlife and plants often thrive (partly) because of this. That adds a further confusion factor.
Clearly the big money is in reducing heat loss in the first place but that has nothing to do with the stark facts when comparing an electrical heater, immersed in water and other small scale methods for making a cup of tea.
This thread could run and run, I think.

 

[artis]

I think you stated it good enough that these solutions might be worthwhile in keeping ambient temperatures within rooms but definitely out of scale for producing lots of energy in a small area in minutes or even hours.

 

[Baluncore]

Engineering involves considering every available possibility, then pruning the options tree only once the economics of each individual application is known.

Heating water is not a fully specified application. There are too many possible confounding variables to rule anything in or out, now or in the future.

 

[Nugatory]

I've never seen a heat pump water heater in a residential setting

Residential heat pump water heaters are available in the US - I’ve spent a lot of time in a house that has one. They are a particularly good fit for a summer house because they turn cold water and hot air into hot water and cold air.

 

[Averagesupernova]

Residential heat pump water heaters are available in the US -

Aren't they a requirement over a certain size? Has been my understanding.

 

[made_change]

Hi! To your Question, Both are electrical heaters with 100% efficiency, but they have varying use and they differ in the way they produce heat. Induction heater, in general, are not used to heat water. Instead, a conventional heating element is a more viable option. In conventional Heater, the current is made to flow through the resistance wire by applying a potential difference while in induction heater, the current is made to flow with the tune of external exciting electromagnetic wave. if you are interested you can go to https://resources.mrheater.in/2019/09/how-induction-heater-works.html for a brief understanding on how an induction heater works.

 

[essenmein]

Heatpump HW heaters do have limitations, specifically the maximum hot side temperature is the problem, from memory its difficult for them to exceed 50-60C output temp without multi stage pumps, basically good for low grade heat at best.

So they are perfect for areas that are warm already, but almost no better than a resistor if the cold side temp drops too much, good luck making them work if your outside air is -20C! As the delta T grows, COP -> 1. At COP 1 a heat pump is a very mechanically complicated resistor!

Induction water/fluid heaters do exist, but generally I've seen them used in applications where heat density is a problem, eg burning the material you want to heat. So for example in milk processing, you want to heat all the fluid to a temp (say pasteurization), but not have a energy density so high that the fluid in contact with the heat source exceeds some limit or burns. Restive elements are also sold with different "densities", if you've ever home brewed properly this would be familiar!

http://waterheatertimer.org/watt-density.html

 

[hutchphd]

Anyone who has used a Metcal soldering iron understands how spectacularly induction heating can deliver lots of power without exceeding a fixed (Curie) temperature.
The other capability of an inductive heater is lack of penetration of the pressure vessel. Most of the appliances rely on coupling to ferromagnetism so if the vessel is not ferromagnetic there is little surface heating.

 

[FJT2]

Makes sense, thanks

I understand that in theory an induction boiler can put the induction coil and the magnetic metal plates inside the tank just like the heating element in an electric boiler. The induction coil doesn't heat up, just the iron in the plates heats up. the plates don't touch the induction coil, so the space allows water to completely surround the plates. as a result they could be just as efficient as a resistive coil. The improved efficiency could come from use of a continuous flow heater that uses an Iron pipe to heat the water on demand, giving instantaneous heat, and eliminating losses due to storing heated water for a long period. Unfortunately the iron pipe may have a relatively short lifespan.

 

[sophiecentaur]

If you are talking in terms of the proportion of electrical energy supplied that provides water heating then you should really include the efficiency of RF equipment to provide the RF power. That makes the simple resistive heating solution the winner.

 

[Baluncore]

The improved efficiency could come from use of a continuous flow heater that uses an Iron pipe to heat the water on demand, giving instantaneous heat, and eliminating losses due to storing heated water for a long period. Unfortunately the iron pipe may have a relatively short lifespan.

Welcome to PF.
You may never beat an immersed resistive element, but you might come a close second.
Why not replace the iron with a thin walled bronze tube that acts as a shorted turn ?
What range of operating frequency would you consider. Maybe down to 50/60 Hz ?
Can you pre-heat water by cooling the primary induction coil and the frequency generator ?

 

[artis]

As @sophiecentaur and @Baluncore already pointed out RF heating is not as efficient as simple resistive heating due to the extra energy being drained in charging discharging the capacitance of the heating element and driving the overall reactance of the circuit.

I guess we could go further and say that even among resistive heating elements the absolute highest efficiency would be for one being fed by DC current as AC even at low frequencies still have some losses due to reactance of the of element and wires, but those are so tiny that I think it would be hard to even measure them.

 

[Baluncore]

... as AC even at low frequencies still have some losses due to reactance of the of element and wires, but those are so tiny that I think it would be hard to even measure them.

The reactance does not cost real watts, only imaginary VAR.

When you need to limit current, such as in or with a solenoid, it is better to use AC with inductance than DC with resistance. That is because the inductive reactance does not generate heat.

To heat something there need to be real watts developed in a resistive element.

 

[artis]

That is because the inductive reactance does not generate heat.

Not by itself but the extra current associated with it does in the form of heat generated within the wire. Isn't this the main reason utilities tend to care about controlling the grid power factor, apart from voltage stability ?

 

[sophiecentaur]

The reactance does not cost real watts, only imaginary VAR.

The wasted I²R power is dissipated elsewhere. "Zere ist no escape Breetish Tommy".
But my initial objection to induction heating was based on what you can buy for cooking etc.. But a beefy transformer could be very local to the heating coil so the low voltage parts of the circuit could involve less loss.
Total cost and scale should also be considered - as in the arguments for Electric Cars - (even down to the transformer and non-mass production of parts).

 

[ZeFrenchman]

I absolutely love this thread. It is one of the clearest demonstration of the complexity of "energy efficiency" discussions on one end, and of how something as trivial as heating water is in fact, a pretty deep and somewhat convoluted thing.
I am one of the few human beings alive having visited multiple electric water heater factories (these guys don't joke around their industrial secrets!) I have been amazed at how complex and counterintuitive heating water can be.
In strictly electric heating, there's no doubt that resistive wins, if for no other reason that there's little else to measure it against and for most of the reasons listed below. In no way does this mean it's the best or the most efficient, but merely that "it's the best we have for the money".
The conductive heat loss is not insignificant and (for most north-american models) hovers around 90W h. So efficiency should also relate to conservation. Or storage. Whatever energy buzzword you want to tack on there.

Efficiency also means having a durable, reliable equipment. And truth be told, the vast majority of EWH elements have grown to be absolute garbage over the past decade, leading to a record number of failures. These are generally not noticed in 2-elements tanks, or at least, not as much.

It's also helpful to know that US-made and Canadian-made EWH are not the same: they do not answer to the same efficiency standards and while they look similar there are key differences in their designs, not the least of which the number of elements and the temperature set point.

Finally, take other means "more efficient" means with a grain of salt: heat-pump EWH are incredibly efficient. They are also the worse possible idea in nothern climates... Geography counts a lot for "efficiency" and one needs to consider that the current resistive type might not be perfect, but it is the sum of all compromises and currently the one that serves us the best. Can we do better ? I sure hope we can :)

As for the OP's question, well, there are people (yours trully being one of 'em) working on induction-based water heating, not out of efficiency concerns, but out of public health concerns. Legionnaire's disease is far more rampant in EWH than most like to admit, and for areas where only electric is an option that are unfortunate to have that particular bacteria in abundance, there needs to be cheaper, more efficient solutions. That's part of what we're working on.

 

[berkeman]

As for the OP's question, well, there are people (yours trully being one of 'em) working on induction-based water heating, not out of efficiency concerns, but out of public health concerns. Legionnaire's disease is far more rampant in EWH than most like to admit, and for areas where only electric is an option that are unfortunate to have that particular bacteria in abundance, there needs to be cheaper, more efficient solutions. That's part of what we're working on.

Welcome to PF.

Can you say more about how inductive heating can help cut down on the bacteria that cause Legionnaire's disease? It seems like you are right that it can be a problem for resistive WH designs:

https://plumbingperspective.com/does-your-hot-water-heater-protect-you-from-legionnaires-disease

 

[ZeFrenchman]

Welcome to PF.

Can you say more about how inductive heating can help cut down on the bacteria that cause Legionnaire's disease? It seems like you are right that it can be a problem for resistive WH designs:

https://plumbingperspective.com/does-your-hot-water-heater-protect-you-from-legionnaires-disease

The prime issue with EWH and Legionnaire's is the configuration of the pressure vessel: with the resistive element a few inches from the bottom, there is a layer of cold water that simply never gets heated. And before someone screams equilibrium, the fact of the matter is that an EWH will typically never rest long enough (at least 3-4 days, in the best of cicumtances) to reach that state. Stratification is well known in WH but it is more problematic in electric, as that bottom layer will never get heated. The bottom is also, unfortunately, where the sludge of biofilm gets deposited, providing a superb environment for both areobic and anaerobic critters. Add to that a broken lower element, and you have yourself a petri dish of Legionella pneumophilae...

I'll add as a political statement that US-made EWH are somewhat worse in that fashion than Canadian-made EWH: in the US, an EWH is asked to "deliver hot water". So it makes sense to have 1 or 2 elements closer to the top of the tank, to provide faster recovery and more deliverability. This also means that the "cold zone" at the bottom is waaaay cold, a problem compounded by the fact that most state mandate 50°C as a storage setpoint. So, a perfect growth environment if contaminated.

Canadian-made EWH are tested to "keep water hot", meaning they want their bottom element closer to the bottom to promote uniformity, at the cost of a slower recovery time. As well, federal law mandates that water be stored no lower than 60°C.
Now, I'm cynical enough to accept that this is by accident, rather than design, but the problem exists nevertheless and the fact that EWH are now being promoted to the rank of energy storage devices in homes means we need to take a long look at that problem that went unnoticed or ignored for decades.

Gas-fired WH circumvent the issue by roasting the biofilm to a crisp with each cycle, so we are trying to achieve a similar effect with in induction-fired WH, where we can eliminate that cold bottom layer. The alternative of course is high-temperature WH, but that's a different beast and these make sens in different settings (think solar heating, energy storage, et al). Also, HTWH bring a load of new issues to the table (mixing valves, pressure vessel material, insulation, etc) and that's some distance out in left field from the original topic :)

 

[ZeFrenchman]

And on the topic of tankless WH: they certainly do help the bacteria growth issue, but unless they are gas fired, they should be considered an abomination to our not-so-modern North American power grid: it just can't take the strain of toasting your bread, making your coffee AND charging your car, let alone heating your shower at the same time... That dynamic alone warrants that we look into different EWH solutions, even at the cost of apparent efficiency, if it means displacing load on the power grid.

It's another direction to that topic, but it ties well into the conversation.

Full disclaimer: the reasoning above is only sound in my world, the frozen hell of Hoth. Not so much in warm-weather geography or where wind/sun/thermal might be available on the cheap.

 

[artis]

@ZeFrenchman or should I greet you by "Salut!"?

What you say is interesting. Where I live we use a lot of electric "boilers", almost every other home has one, as the only other option to heat water is from the heating furnace that heats the house to pass through circulation through an accumulation boiler, which is also another popular way, the third is to use natural gas.
Honestly I have never heard of a single outbreak in the past couple of decades , well I have heard about them but in fact not in association with the boilers, rather in places where water has been stagnant for a long time, like cases where owners go for a long trip or the flat/house isn't inhabited for some time.
Could it be that it is more prevalent for standing water?
I myself have a electric boiler which works exactly like you described, vertical pressure vessel, heating element resistive and placed at the bottom.

One other important thing is to clean them regularly. I clean myself either once a year or twice , lately the water quality has become better so once is enough.

I am not sure with this one so correct me but I would think the filtration of the city water supply before it is even pumped into pipelines for distribution to houses is also important, in Europe we in general tend to have strict controls over that to prevent microorganisms from building up in the pipes.
But as I said I have mostly only heard about the disease with respect to long standing water , wherever water is used regularly I have never seen a problem with it.

But it seems your logic is correct, a heating supply that heats the water and surrounding container evenly to high temp is better than one which only partially heats to high temp while leaving other parts to lower temps where bacteria can thrive, combine that with a local badly filtered supply coming from a lake or ground/river and you potentially have problems