Induction Water Heaters: Are They Worth It?

[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?