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Old 06-01-2021, 05:23   #1
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Electric hot water heater / Legionella bacteria concerns

How do people deal with Legionella concerns when it comes to mostly electric hot water heater setups?


When we upgrade the electrical systems on our cat, we would like to have less of a reliance on running the engines to get hot water. I understand the engines get the temp in the tank hot enough to kill the Legionella bacteria. But, is this practical / possible with a mostly electric solution (i.e. we only want to heat water when we need it, not all the time and ensure the Legionella bacteria is killed)?


Everyone seems to be telling us to "forget it, just run the engines" but we want to explore other options.


Thanks.
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Old 06-01-2021, 05:29   #2
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Re: Electric hot water heater / Legionella bacteria concerns

Do you have legionella concerns with the electric water heater in your house?
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Old 06-01-2021, 05:31   #3
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Re: Electric hot water heater / Legionella bacteria concerns

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Originally Posted by NaClyDog View Post
How do people deal with Legionella concerns when it comes to mostly electric hot water heater setups?


When we upgrade the electrical systems on our cat, we would like to have less of a reliance on running the engines to get hot water. I understand the engines get the temp in the tank hot enough to kill the Legionella bacteria. But, is this practical / possible with a mostly electric solution (i.e. we only want to heat water when we need it, not all the time and ensure the Legionella bacteria is killed)?

Everyone seems to be telling us to "forget it, just run the engines" but we want to explore other options.

Thanks.
Every electric water heater for sale is safe because it heats water to high enough temperature, then the output is mixed with cold water by a thermostatic mixing valve so that no scalding hot water arrives at the faucets. I recommend an IsoTherm water heater.
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Old 06-01-2021, 05:32   #4
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Re: Electric hot water heater / Legionella bacteria concerns

Get a dual system a hot water tank with electric element and an engine coil. Heat with electric on the dock and get free hot water whenever the engine is run.


Most marine calorifiers are made like this.
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Old 06-01-2021, 05:32   #5
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Re: Electric hot water heater / Legionella bacteria concerns

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Do you have legionella concerns with the electric water heater in your house?
Nope but it is running 24 / 7. If the water isn't either continuously kept at temp or heated to 60C - 70C long enough to kill the bacteria then I definitely would.
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Old 06-01-2021, 05:36   #6
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Re: Electric hot water heater / Legionella bacteria concerns

Basic Rules to prevent the proliferation of Legionella
Hot water must be stored at a high temperature, as a precaution against bacteria*. It can be delivered from the tap at a lower temperature to prevent scalds.

The (terrestrial) solution to the temperature dilemma, is to use a quality mixing valve, to allow VERY hot water to go to the dish washer and laundry machines to actually kill GERMS, and use these tempering valves to control the temperature of the water, after these devices to go throughout the system.
Now when this hot water reaches a shower or faucet, you can add safety devices called pressure/temperature regulating/valves, or balancing valves, etc. What these devices do is protect the user from being scalded, when someone else flushes a toilet, and the pressure drop is acted upon, with no chance of the user being burned.

* For example, temperatures under 50 C may increase the risk of Legionnaires’ disease, a form of pneumonia, due to bacterial growth in the tank. That disease is caused by Legionella bacteria, which live in water. Temperature is a critical factor for Legionella to grow. The risk of colonization in hot water tanks is significant between 40 and 50 C. Drinking contaminated water is not a major cause of Legionnaire’s disease.
https://www.cruisersforum.com/forums...tml#post284888

Water temperatures are critical:
Keep cold water below 20̊C (68̊F) maximum
Keep stored hot water above 60̊C (140̊F) minimum
Keep the return temperature of a secondary return system above 50̊C (122̊F) minimum

Legionella thrives in warm environments 25 to 45 ̊C (77 to 113 ̊F).
According to Reliance WorldWide:

Temperature affects the survival of Legionella are as follows:
* 70 to 80 ̊C (158 to 176 ̊F): Disinfection range
* At 66 ̊C (151 ̊F): Legionellae die within 2 minutes
* At 60 ̊C (140 ̊F): Legionellae die within 32 minutes
* At 55 ̊C (131 ̊F): Legionellae die within 5 to 6 hours
* Above 50 ̊C (122 ̊F): They can survive but do not multiply
* 35 to 46 ̊C (95 to 115 ̊F): Ideal growth range
* 20 to 50 ̊C (68 to 122 ̊F): Legionellae growth range
* Below 20 ̊C (68 ̊F): Legionellae can survive but are dormant
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Old 06-01-2021, 05:37   #7
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Re: Electric hot water heater / Legionella bacteria concerns

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Originally Posted by s/v Jedi View Post
Every electric water heater for sale is safe because it heats water to high enough temperature, then the output is mixed with cold water by a thermostatic mixing valve so that no scalding hot water arrives at the faucets. I recommend an IsoTherm water heater.
Thank you. The sales specs I have seen on marine hot water heaters weren't clear if they got hot enough while running on electricity.


Cheers.
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Old 06-01-2021, 05:40   #8
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Re: Electric hot water heater / Legionella bacteria concerns

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Thank you. The sales specs I have seen on marine hot water heaters weren't clear if they got hot enough while running on electricity.


Cheers.
The danger is when you would not allow it to get hit enough by cutting power before the thermostat reaches shut off temperature. We simply switch it on and watch power consumption to see if it’s hot. The element consumes 750W
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Old 06-01-2021, 06:44   #9
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Re: Electric hot water heater / Legionella bacteria concerns

I know my Raritan water heater has an adjustable thermostat, so if in doubt, you could just turn it up a bit hotter. IIRC, mine is set somewhere in the 140 - 150 degree range. Any time I'm heating water on generator power, I let it run through the full heating cycle until it shuts off.



I worry more about the water sitting in the lines. The tank stays cool, but a lot of my water lines are in the engine room, so they spend plenty of time right in the not-good temperature range.
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Old 06-01-2021, 06:48   #10
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Re: Electric hot water heater / Legionella bacteria concerns

I know a lot of people worry about hot water tanks and legionnaires.
Why do we not hear of it from all the boats in Granada through the summer?
From Gord May's post(which I believe to be correct)
* 35 to 46 ̊C (95 to 115 ̊F): Ideal growth range

* 20 to 50 ̊C (68 to 122 ̊F): Legionellae growth range

The water tanks on many boats are above the water line. air temps are well above 20°c and do get up to 50°c. And maintaining these temps for days or weeks. So why is nobody concerned about the cold water tank, that's what we are drinking from?
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Old 06-01-2021, 06:52   #11
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Re: Electric hot water heater / Legionella bacteria concerns

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I know a lot of people worry about hot water tanks and legionnaires.
Why do we not hear of it from all the boats in Granada through the summer?
From Gord May's post(which I believe to be correct)
* 35 to 46 ̊C (95 to 115 ̊F): Ideal growth range

* 20 to 50 ̊C (68 to 122 ̊F): Legionellae growth range

The water tanks on many boats are above the water line. air temps are well above 20°c and do get up to 50°c. And maintaining these temps for days or weeks. So why is nobody concerned about the cold water tank, that's what we are drinking from?
This thread is about hot water heater concerns but, to your point, maybe they have proper filtration in place? I don't know, that is just a guess.
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Old 06-01-2021, 07:29   #12
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Re: Electric hot water heater / Legionella bacteria concerns

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Originally Posted by Sailmonkey View Post
Do you have legionella concerns with the electric water heater in your house?
I don't, but I know that local water supply authorities chlorinate the water to a level that kills Legionella, as do water authorities across the US. The water that goes out into the distribution system intentionally has a residual amount in it to kill anything in the system. Since the system is sealed, that residual amount remains in the water.

While you can chlorinate the water tanks, they should be vented so whatever is added will evaporate from the tank in a matter of hours. The question then becomes how likely are any number of pathogen likely to make it into the tank prior to the next time you dose it.
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Old 06-01-2021, 07:46   #13
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Re: Electric hot water heater / Legionella bacteria concerns

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Originally Posted by NaClyDog View Post
This thread is about hot water heater concerns but, to your point, maybe they have proper filtration in place? I don't know, that is just a guess.
Sorry about the thread drift. It just seemed a significant concern, since the water tank feeds the hot water tank. If growth is happening in the main water tank, it would be prudent to adress it there as well.
Another option to look at is 12 volt elements, or solar heaters with a small circulation pump.
After we upgrade our solar this summer, my plan is to add a 12 volt element so we can utilize leftover solar energy once we hit float. The goal being to achieve minimum 60° c. So there will be some math involved to make sure we use a big enough element.
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Old 06-01-2021, 07:57   #14
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Re: Electric hot water heater / Legionella bacteria concerns

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Originally Posted by NaClyDog View Post
This thread is about hot water heater concerns but, to your point, maybe they have proper filtration in place? I don't know, that is just a guess.
Nope, people regularly use the fresh water tanks. Sometimes, they dose it with a little choline bleach but this is usually once every few months, so plenty of time for regrowth.

As indicated by Gord's post, getting up to 140F will quickly kill the bacteria. Keep in mind, these heaters are insulated so even if you shut it off after reaching temp (typically around 160F), it will stay hot long enough to kill them off (we've had hot water in the morning after 12-14hr turning it off in the evening)
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Old 06-01-2021, 09:47   #15
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Re: Electric hot water heater / Legionella bacteria concerns

That bacteria is dead at 130 F. End of story !
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