electric water heater temperature and bacteria

hjihjiApril 6, 2007

Hi. I am about to install a new electric water heater to replace the one we have. I was talking to a plumber and he told me that electric water heaters need to be set to 140 degrees, and the outgoing water needs to be tempered with a mixing valve (add cold water to the outgoing hot water). He said the reason for the high temperature is kill bugs growing in the water. Legionaire's disease bacteria is suspected to grow in 120 degree electric water tanks.

Has anybody heard of this before? Is this for real? I was going to turn my temperature down low, but now I'm not sure. Also, if I do need a high temperature, can I keep it lower most of the time and just "pulse" it occasionally (couple hours per day), to cook the water?

thanks.

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fsq4cw

Your plumber is correct.

HereÂs what we did a few years back, and weÂre very happy with our choice. We installed an electric OSO stainless steel 62-gallon hot water tank. Water temp is 175ºf. Internal cold water mixing valve reduces output temp to 120ºf when there is a demand for hot water.

This high temperature with the cold water mixing achieves 2 important things. First, the high storage temperature greatly reduces the risk of growing pathogens in your tank, such as legionnaires disease, which may be inhaled as an aerosol when showering. The 2nd accomplishment is that due to the higher storage temperature and the cold water internal mixing valve, the 65-gallon (Imp.) tank now has the equivalent hot water of a 90-gallon (Imp.) tank (108 Gal. U.S.) without taking up any additional space.

We have NEVER run out of hot water.

This tank is stainless steel; it will last MANY times longer than a conventional tank. You have much greater peace-of-mind when away on vacation that this tank will NOT rust out and burst.

I would strongly suggest not tampering with the temperature or turning the tank off when youÂre away.

HereÂs a link to their site:

http://www.oso-hotwater.com/ca/index.htm

SR

Here is a link that might be useful: Water temperature - a degree of importance

    Bookmark   April 7, 2007 at 12:30AM
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garyg

There goes saving energy with the hot water tank.

    Bookmark   April 7, 2007 at 10:19AM
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mr_havac

"There goes saving energy with the hot water tank."
AMEN, now that you wasted all your money on hot water you won't be able to pay for your own funeral when something else kills you!

    Bookmark   April 7, 2007 at 10:26AM
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jrdwyer

Are there any scientific studies that show a correlation between legionnaires disease and 120F water temp. in electric water heaters that you are suggesting?

Our water utility uses filters and chlorine to sanitize water taken from our local 'dirty' river before we drink it. How does this affect the chances of getting legionnaires disease from shower water droplets at 120 degrees F?

    Bookmark   April 8, 2007 at 10:00AM
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baymee

This topic came up before and fsq4cw has posted accurate information, but I remember the stats as saying that you are more likely to die from slipping on a banana peel.

    Bookmark   April 8, 2007 at 11:50AM
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mr_havac

Does it matter what temperature the banana peel is?

    Bookmark   April 8, 2007 at 3:45PM
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baymee

Pickled. It can be kept at any temperature.

    Bookmark   April 8, 2007 at 6:20PM
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garyg

So it's OK to keep my hot water tank at 125 F as long as there are no banana peels in the area?

    Bookmark   April 9, 2007 at 7:15AM
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mikie_gw

As long as you take a shower or two per day, you're not going to be growing much bacteria. There's always Dial anti-bacteria deodorant soap.

    Bookmark   April 9, 2007 at 9:53AM
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garyg

If I take a 125 degree shower with Dial anti-bacterial/anti-Legionaire's soap and no banana peel in the shower, I should be safe. But what about Anthony Perkins with a large knife waiting outside the shower?

    Bookmark   April 9, 2007 at 10:24AM
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baymee

If you take a 125 degree shower, you will be scalded to death and won't be able to respond to any questions.

    Bookmark   April 9, 2007 at 11:16AM
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garyg

You are very fussy, Baymee (but indeed correct).

To re-phrase: If I take a shower with my hot water tank set at 125 degrees, and I use Dial anti-bacterial/anti-Legionaire's soap, and Anthony Perkins is outside of the shower with a large knife, but he is indeed standing next to a pickled banana peel at room temperature, will I be OK???

    Bookmark   April 9, 2007 at 1:58PM
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baymee

And a mixing valve set for 104º :) and anti-skid material near the banana peel.

    Bookmark   April 9, 2007 at 2:25PM
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bus_driver

I don't like taking showers. It won't "stay done". Kinda like washing dishes or mowing the lawn. You can do it today and three weeks later it has to be done again.

    Bookmark   April 9, 2007 at 4:50PM
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fa_f3_20

You are all confusing it with Colonel Mustard and a candlestick in the drawing room.

    Bookmark   April 9, 2007 at 5:11PM
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fsq4cw

Sounds to me like you guys Âdrank the cool-aidÂ!

SR

    Bookmark   April 9, 2007 at 7:27PM
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baymee

Hey, Let's go back over to the HVAC turd post. It's dropping off the list.

    Bookmark   April 9, 2007 at 8:09PM
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tl45

"This topic came up before and fsq4cw has posted accurate information, but I remember the stats as saying that you are more likely to die from slipping on a banana peel."

that misses the point. Legionella is more likely to kill you than scalding from high water temps.

This is a serious topic as codes and recommendations around the US and Europe are being revised. Indeed houshold hot water heaters may have to have mixing valves in a few years.

I did some research on this one looking into my high low cold water temps at my washer and someone recommedned a similar mixing valve.

the incidence of Legionnaires' disease is increasing and deaths are probably underreported.

Contributing risks factors are electric water heaters (vs gas) and decontamination with Chlorine instead of Chloromines.

If you have an electric hot water heater you should have a mixing valve ad go for 140.

Unfortunately the same risk factors for scalds result in high death rates from legionella -- young children and the elderly.

"There goes saving energy with the hot water tank."

In fact yearly savings from going from 140 to 120 are minute -- especially for indoor installations or temperate climates.

    Bookmark   April 15, 2007 at 2:19PM
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fsq4cw

Re: tl45

Thanks for your interesting post. Heat losses from a hot water tank are not serious in climates that require mostly heating. Any Âloss during heating season contributes to heating the house just as using an oven or fridge does. ItÂs mainly a serious loss when heating is not required, particularly during air-conditioning season.

Scalding is not a problem due to an effective internal mixing valve in the hot water tank. We also use Grohe shower taps (the best brand IÂve EVER seen) that are temperature balanced, a superior design, rather than pressure balance. Just dial up the desired temp and thatÂs what you get until the water reserve in the tank drops below the tap set point, irrespective of other water demands within your home, hot or cold.

Incidentally, for a family of 3.5 (daughter moved out mid year), and a HW tank capacity of 76 gal. U.S. at 175ºf, we consumed 3014kWh ($195.CDN w/Tx) for 362 days; for what itÂs worth.

SR

Here is a link that might be useful: Grohe

    Bookmark   April 16, 2007 at 11:37AM
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garyg

"the incidence of Legionnaires' disease is increasing and deaths are probably underreported"

- Until this post, I have not heard of Legionnaire's disease in hot water tanks. Nothing in the news, nothing from the electric company. Maybe I am just uninformed.

    Bookmark   April 18, 2007 at 2:31PM
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don21

Heat loss from any water tank is a significant percentage of the overall energy usage - That's why you save energy by putting your water heater on a time clock and only applying energy to it for a couple hours per day . . . . most folks use far more electricity keeping the water warm than they do heating it in the first place

Energy losses in a 175 degree water tank would be VERY large. I have a pair of the 55 gallon Sears Best 12 year heaters with 3 inches of foam insulation in use with my solar heating system which frequently generates temperatures in the 155 to 160 degree range and if the tanks are at 160 when the sun goes down, they are both down to about 125 to 130 degrees by the time the sun comes up the next morning. Not too hard to figure how much electrical energy would be necessary to reheat the 110 gallons of 130 degree water back up to 160 degrees and that would give you an idea of the heat losses over about a 12 hour span - Nothing trivial I assure you. Lucky for me that neither of my water heaters even have the electricty turned on about 10 months out of the year, so the elevated losses caused by storing hotter than usual water don't cost me a dime, but if you have a heater hooked up to power and you're intending to keep it at 175 degrees you'll know the difference as soon as you check your first couple of power bills

Considering the odds of getting sick from a 120 degree water tank versus the energy wasted by maintaining a 175 degree tank I would certainly opt for the 120 degree setup - I've never met anyone who caught Legionnaires disease . . . . but I know lots of folks wasting lots of energy with their water heater thermostats turned up way too high

Don

    Bookmark   April 18, 2007 at 10:51PM
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baymee

The statistics are variable, but about 2200 people a year die from Legionnairs disease and one of the causes is indeed the domestic hot water tank.

However, 17,000 people die each year from slips. Both causes of premature death are unfortunate, but I'll be keeping my eye out for the banana peel on the floor before I worry about the shower mist.

    Bookmark   April 19, 2007 at 2:59PM
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garyg

So it goes back to my post from a week ago:

"If I take a shower with my hot water tank set at 125 degrees, and I use Dial anti-bacterial/anti-Legionaire's soap, and Anthony Perkins is outside of the shower with a large knife, but he is indeed standing next to a pickled banana peel at room temperature, will I be OK???".

I have my choice between Legionanaire's disease, a slippery banana peel, or Anthony Perkins w/large knife.

    Bookmark   April 19, 2007 at 10:20PM
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baymee

Next time you take a shower, turn the hot as far as you can stand it and measure the temp. I bet it'll be around 106.

    Bookmark   April 20, 2007 at 5:50AM
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brickeyee

"Not too hard to figure how much electrical energy would be necessary to reheat the 110 gallons of 130 degree water back up to 160 degrees...."

About 27,500 BTU or 8.07 kW-hr.

At $0.07 a kW-hr it would cost a horrifying $0.57 or so.
Less than one dollar.
If you know the surface area of the tanks the R value can even be computed from the losses if you assume the room temperature remains constant.

    Bookmark   April 21, 2007 at 1:37PM
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don21

I WISH I could buy electricity for 7 cents per kilowatt hour

Still at just a dime, that's 80 cents per each 12 hour period of time, or $1.60 per day times 365 days per year which equals a pretty substantial $584 per year - Far more than a new water heater costs

Since my solar panel does this for free, not to mention the fact that it also heats my 65 degree well water up to the previously mentioned 130 degrees, I would have to guess that it's saving me more than $1K per year - If so, I'm looking at less than a 3 year payoff for the money I invested in the system ;-)

Don

    Bookmark   April 21, 2007 at 6:00PM
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scott2006

The fellow next door turned his hot water tank down and was in the hospital 2 times with the L disease. He almost died. Check with you health department I'm sure they have details on the problem.
Good Luck. Scott

    Bookmark   April 22, 2007 at 6:16PM
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garyg

"The fellow next door turned his hot water tank down and was in the hospital 2 times with the L disease."

- I have never heard of a fellow going to the hospital for Lesbian disease.

    Bookmark   April 23, 2007 at 8:08AM
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mikie_gw

He was an Odd Fellow.

    Bookmark   April 23, 2007 at 8:23AM
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vstech

does anybody worry about drowning from looking up into the shower head while showering? that's another possible danger from the shower.
John

    Bookmark   April 27, 2007 at 12:19AM
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elctrafied

Install a tankless saves money cost more to buy.Im away during the week not much water used only comes on when hot water is turned on at faucet.

    Bookmark   April 27, 2007 at 1:26PM
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mr_havac

"I have never heard of a fellow going to the hospital for Lesbian disease'
I wonder how long it takes to get that problem licked?
:-o

    Bookmark   April 27, 2007 at 10:56PM
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