Induction Water Heaters: Are They Worth It?

[ZeFrenchman]

@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

Et salut à toi ;)

Yes, geography matters a great deal when it comes to the Legionella conversation, since areas see both various water heating technologies and exposure to the bacteria. But last we checked, not a single water utility (in North America anyway) filtered or otherwise treated water against Legionella pneumophila, a bacteria found in many water ways around the world. Frankly, I'm not certain they could even if they wanted to...

Standing water does increase biofilm, thus risk, but isn't a requirement to bacteria growth in water heaters, mostly because of the advantage provided by the mild water temperature. France has seen its fair share of challenges with this in the early 00's if memory serves.

The challenge in under-reporting and the associated issues in sampling (See Dr Janet Stout on that topic, great work) is exactly that: under reporting. Whenever an outbreak appears, it drives ressources and energy to finding the source, often times an HVAC cooling tower or some public water feature. But when people, usually a single person, shows up at the hospital with Legionaires and often enough dies from it, no one ever investiguates.

And unfortunately, once corrected for under reporting, the stats can be a lot grimmer: Dr.Michel Plante (Hydro Quebec, Canada) reported recently that he figured 7 people died yearly from Legionaires contracted from their EWH (which makes up the majority of WH in that area). Some argue that his studies take a few shortcuts, but the fact remains that somewhere between "no problem" and "we'll all die from a hot shower" lies a poorly documented and understudied problem.

 

[anorlunda]

no one ever investiguates

My best friend is retired from the US Public Health Service. He spent almost all his time in recent decades running to every outbreak to investigate.

 

[anorlunda]

My son is a licensed plumber. He says that the plumbing code in his state specified 120F (50C) as the maximum legal hot water temperature. Scalding burns are possible if hotter.

However, the legionnaires literature here says that hot water tank temperatures must not be lower than 60C (140F) to prevent growth of the bacteria.

Both can be satisfied with a mixer between tank and faucet that blends hot water with cold water to guarantee water no hotter than 120F at the faucet, regardless of tank temperature. But I've never seen a residence with such a mixer.

My son also said that using up your hot water, prevents it from being stagnant. Problems occur if hot water is stored weeks or months below 60C with no circulation. Hot tubs have that situation more often than hot water heaters.

 

[Baluncore]

All is lost without the technology to contain and heat water.
You know you are civilised, when you can make a hot cup of tea.

 

[Tom.G]

My best friend is retired from the US Public Health Service. He spent almost all his time in recent decades running to every outbreak to investigate.

And his general conclusions are?

 

[artis]

And his general conclusions are?

All is lost

 

[ZeFrenchman]

Well, that escalated quickly... ;)

 

[ZeFrenchman]

My best friend is retired from the US Public Health Service. He spent almost all his time in recent decades running to every outbreak to investigate.

To clarify: Legionnaires disease is a reportable disease in most countries with a solid public health system. This means that there generaly are investigations for reported cases, but they are generally centered around reports with more than one case for a general area as it often points to a community source (think of a HVAC cooling tower on top of a building blowing bacteria in the wind...). As literature points out however, investigating individual cases and the technical difficulty of sampling water heaters makes it nearly impossible to identify and link bacterial sources to an individual's disease.

Technological advances in DNA field analysis might help this in the future.

 

[ZeFrenchman]

My son is a licensed plumber. He says that the plumbing code in his state specified 120F (50C) as the maximum legal hot water temperature. Scalding burns are possible if hotter.

Funny enough, the consensus around the scalding temperature seems to be a correlated with litigation: a very cynical research collaborator once told me: "burn victims cost a fortune, dead people can't sue". A bit harsh, but it does seem to represent the industry's desire for lower water temperature vs preventing bacteria growth in systems. That particular aspect isn't much of an issue for residential, but it seems to be responsible for many outbreaks in institutional settings.

Both can be satisfied with a mixer between tank and faucet that blends hot water with cold water to guarantee water no hotter than 120F at the faucet, regardless of tank temperature. But I've never seen a residence with such a mixer.

True and it's certainly part of the solution. We have a number of consumer-grade high-temperature water heaters on trial here and they all have a built-in mixing valve. It does look promising.

My son also said that using up your hot water, prevents it from being stagnant. Problems occur if hot water is stored weeks or months below 60C with no circulation. Hot tubs have that situation more often than hot water heaters.

Also very, very true about hot tubs or whirlpools. They are certainly guilty of harboring nasty critters (I'm also told that it would explain in great part their disapearance from hotels and such). For the water heater, using it up might not do much unfortunately, since the pressure vessel doesn't "circulate" per se. Depending on make an model, some areas of the tank can remain fairly undisturbed, specially at the bottom, where evil lurks...

 

[russ_watters]

You know you are civilised, when you can make a hot cup of tea.

On a campfire, in a clay pot?

 

[russ_watters]

The risk of legionella is certainly not zero, but it's pretty speculative to say that there is a high risk that isn't documented. Without evidence, it's just a guess. The CDC does list water heaters, and I see sources speculating on the impact of buildings going vacant due to COVID, but I'd like to see real research/stats into sources of actual infection.

I'm in HVAC and of course it is a big concern in cooling towers and air conditioner condensate, but as others suggest I'm not even seeing a logical reason why it would be a significant risk for water heaters, much less documented evidence of the risk.

Further, legonnaire's is a lung disease. You get it by breathing the bacteria, not drinking it. It's obvious how a cooling tower or air conditioner would promote inhalation, but less obvious/efficient for, say, a drinking fountain.

But as I said, I'm an engineer, not an epidemiologist.

 

[anorlunda]

I would like to add a new factors in this discussion of water heating to remind everyone to remember minority use cases and not just mainstream use cases. The topic of heating water can be very broad.

I live in an RV with 1500 watts electric service. To use the AC I need to shut the hot water off.

I was considering a DIY solar HW heater project.

But that needs a circulation pump, plus a way to prevent overheating/overpressurization, and a way to drain it when I leave for the winter to prevent freezing, or to fill it with antifreeze and use an intermediate heat exchanger. The complexity adds up fast. My DIY skills and DIY tools are very limited.

Instead, I intend to use the existing water heater's solutions for all those problems. I plan to get a 200 watt solar panel, plus an inverter. I'll swap the 1200w resistive heating element for a 150w element. Then I can disconnect the entire system from the grid and feed it from the inverter. No parallelization of inverter and grid. No mains electric. No safety problems with rewiring the internals of a water heater. I'm not concerned with fast HW recovery, or about running out of HW during the night.

We also lived on a sailboat for 12 years. We had no HW tank. In those years, we found that a sun shower was a delightful source of hot water for showers. It heats up in only 30 minutes at midday. And showering on deck in a bathing suit with the bright sunlight and open air feels good. In places like The Bahamas, fresh water is scarce. The Sun Shower also had the benefit of saving fresh water. 4-6 liters was ample for one shower.

 

[Tom.G]

I'll swap the 1200w resistive heating element for a 150w element.

You may want to check what the maximum water temperature will be with that 150W heater. You could end up shooting yourself in the foot if the water is maintained around body temperature -- ideal temperature for the nasties to grow.

Try to measure the water temperature drop over a period of time. That, along with the water volume, unit conversions, and some arithmetic, will yield rate of heat loss at present ambient temps.

EDIT:
Oops! I missed the post where that was mostly addressed.
The conductive heat loss is not insignificant and (for most north-american models) hovers around 90W h.

Cheers,
Tom

 

[sophiecentaur]

But I still can't imagine that the losses in the induction 'amplifier' can be ignored compared with 'no loss' with a resistor within the water.

I was wondering whether a heat pump arrangement could be used to heat some circulating water to a safe temperature and then using that heat to heat up the next lot. I think perhaps two reservoirs of water would be needed for the system to work without actually mixing the previously heated water with the not-yet heated water.

These things make me feel so old. Legionnaire's disease was not heard of when I was a lad. Suddenly, everyone was getting it.

 

[anorlunda]

Try to measure the water temperature drop over a period of time. That, along with the water volume, unit conversions, and some arithmetic, will yield rate of heat loss at present ambient temps.

That would be a useful experiment. Thanks Tom. Actually, I have the same situation in two RVs, but one of them has a 20 gallon tank electric, and the other one has a small tank maybe 5 gallons electric/propane. The two may give very different results.

 

[ZeFrenchman]

The risk of legionella is certainly not zero, but it's pretty speculative to say that there is a high risk that isn't documented. Without evidence, it's just a guess. The CDC does list water heaters, and I see sources speculating on the impact of buildings going vacant due to COVID, but I'd like to see real research/stats into sources of actual infection.

I'm in HVAC and of course it is a big concern in cooling towers and air conditioner condensate, but as others suggest I'm not even seeing a logical reason why it would be a significant risk for water heaters, much less documented evidence of the risk.

Further, legonnaire's is a lung disease. You get it by breathing the bacteria, not drinking it. It's obvious how a cooling tower or air conditioner would promote inhalation, but less obvious/efficient for, say, a drinking fountain.

But as I said, I'm an engineer, not an epidemiologist.

It's actually fairly well documented. The part I complain about is the lack of awareness about said studies and documentation. ASHRAE has documented the phenomenon extensively, albeit mostly in institutional settings. Special Pathogen Laboratories and their various commercial counterparts have also produced a lot of reports on the topic. I believe Dr Janet Stout's team might be the only one that has extensively looked at it from the residential perspective, in English anyway. There is extensive research that has been done in Quebec, as the state-owned utility decided to sell its water heater rental business in a hurry back in the early 00's, citing - internally of course - a "reputational risk" associated with, well, people dying from using their water heaters. While heavily poticized, that story has yielded a lot of good data. All in French of course :)

The bottom line is that 1 in 3 is contaminated, and 1 in 5 is set a temperature that is too low or has a defective bottom element. Where you are correct in saying about a guess, it's that last line between that data and the reported yearly cases in Legionaires (and to be precise, those that occur in winter, where no cooling tower can be blamed, at least here in the northern climates). That's the part that really needs a better focus methinks.

As for the infection path, it's the shower. To a lesser extent, faucets in general, but mostly either shower head or unsufficiently heated water sprayed in the shower. ASHREA's 188 committee is and has discussed this fairly extensively.

I'll try to come up with the references and links I mention here in a comprehensive list, but I also realize I've completely hijacked this thread, now way beyond what the OP asked. I'll probably start another one.

 

[gwnorth]

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.

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

Unless you happen to have an embedded pacemaker. People with pacemakers need to stay away from induction appliances.

 

[DaveE]

Unless you happen to have an embedded pacemaker. People with pacemakers need to stay away from induction appliances.

"Man dies from hugging his water heater" is a headline I don't think we'll see soon.

https://pubmed.ncbi.nlm.nih.gov/16635999/

 

[sophiecentaur]

This has been an over-long thread, imo and that may be due to the use of the word "efficient", which could perhaps be replaced usefully with "effective". Then we would know better what to be discussing.

 

[RICOCHETAZ]

It's actually fairly well documented. The part I complain about is the lack of awareness about said studies and documentation. ASHRAE has documented the phenomenon extensively, albeit mostly in institutional settings. Special Pathogen Laboratories and their various commercial counterparts have also produced a lot of reports on the topic. I believe Dr Janet Stout's team might be the only one that has extensively looked at it from the residential perspective, in English anyway. There is extensive research that has been done in Quebec, as the state-owned utility decided to sell its water heater rental business in a hurry back in the early 00's, citing - internally of course - a "reputational risk" associated with, well, people dying from using their water heaters. While heavily poticized, that story has yielded a lot of good data. All in French of course :)

The bottom line is that 1 in 3 is contaminated, and 1 in 5 is set a temperature that is too low or has a defective bottom element. Where you are correct in saying about a guess, it's that last line between that data and the reported yearly cases in Legionaires (and to be precise, those that occur in winter, where no cooling tower can be blamed, at least here in the northern climates). That's the part that really needs a better focus methinks.

As for the infection path, it's the shower. To a lesser extent, faucets in general, but mostly either shower head or unsufficiently heated water sprayed in the shower. ASHREA's 188 committee is and has discussed this fairly extensively.

I'll try to come up with the references and links I mention here in a comprehensive list, but I also realize I've completely hijacked this thread, now way beyond what the OP asked. I'll probably start another one.

ZeFrenchman, your hijack of the thred I found fascinating! Sorry to the original poster. In my search of cooling rod materials for nuclear reactors, I landed here!

 

[artis]

cooling rod

didn't you mean moderating rod?