Safest hot water heater temperature setting 120 degrees

chambleemamaJanuary 16, 2009

120 degrees is plenty hot enough for soaps and detergents to work, and it is much safer for small children and the elderly. You can test your actual delivery temperature by holding a cup under the hot water as it runs into the tub or sink and using an instant-read thermometer.

Come to think of it, now that I have a FL washer with an internal heater, I'm going to recheck my hot water.

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From what I have read, there is more chance of bacteria in the water at 120.??

    Bookmark   January 16, 2009 at 7:58PM
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We keep our hot water heater on the "vacation" setting. Makes showers very comfortable and saves on gas. (If we had kids, we might run out of hot water, but its just the two of us.) I wash everything in cold water - it is easier on the fabrics and the colors. DH says that soap is what kills bacteria, not the temperature of the water.

I have not been able to find anything definite to prove that, though.

    Bookmark   January 16, 2009 at 9:51PM
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If you wash everything in cold water you could eventually have soap scum and mold issues in a front loader especially. Ask many folks here with smelly machines.

    Bookmark   January 16, 2009 at 10:43PM
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I just had a home "energy audit". I mentioned that my hot water heater (electric) is set to 140 and I really don't want to lower it. He said (and I'm just repeating what I was told) that I wouldn't see much, if any, difference in my electric bill because I'd be using more hot water to cold to compensate for the lower temperature. More hot water out of the tank, more water to fill it up and more water to heat.

    Bookmark   January 17, 2009 at 12:31AM
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monicakm, you're kind of in the same boat I am. Don't use anywhere near the water in the tank so the bulk of the heating is for maintaining temperature. Where you would notice the difference is the heat loss. Higher water temperature equals a greater difference in temperature between the water and the ambient room temp. This allows for greater heat loss into the room. The heat lost will have to be made up by the heating element. It might be interesting to you to meter the use for a couple months and change the temp and monitor it again to see what the use difference would be. Now some would argue that the heat loss into the room helps heat the room, but that's debatable too.

Many consider a 6%-10% savings in heating costs by turning down the temp from 140° to 120°. Adding insulation can cut the costs, as can using an energy saver switch and possibly even a timer.

I've read a few things about the fear of Legionella, other bacteria and other variables. And yes it appears that electric heaters have more of a problem so many recommend a higher setting on an electric heater than on a gas heater, but having a higher temperature will also increase your calcium deposits, which would shorten the life of the heater, so there's another cost consideration. Possibly a 135°-137° could be a compromise temperature on an electric unit.

Of course far more caution is required with higher temperatures. Often a heater set for 140° can actually build up to 150° or even 160° which can be serious if not careful. It takes 10 minutes exposure at 120° to cause a bad burn, while it takes 2 seconds at 150° and 6 seconds at 140°.

This has been some interesting reading. I've always opposed electric water heaters because of the cost factor around here but now, there seems to be more reasons. Ah, it's always something, isn't it?

I'm curious about the guy I read about a while back who uses only the pilot light on his GWH to heat the water. Obviously that wouldn't work in your situation, but is an example on how little is truly required to maintain water heating to a comfortable level under the right circumstances.

    Bookmark   January 17, 2009 at 1:35AM
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I have my electric hot water heater on the lowest setting there is. My kids love it because they don't have to spend time adjusting the hot and cold water. My husband takes a shower first and then the kids which makes the water comfortable for them. We never run out of hot water either because we turn the water off when we soap up. My hydro bill used to be about $120.00 and now it is only around $82.00. That is summer and winter because we also use a wood stove which I also use to heat water for dishes and cleaning. Major savings!! I use my kettle to heat the water that I need in the summer. People don't realize that when they run there hot water to wash their hands it takes a little bit of time for the water to get to the tap, then the hot water just sits in the pipes which is such a waste. We use hand sanitizer after using the washroom so there is no need to run the water. I was a little worried about bacteria because people have told me that the water must be hot enough to kill bacteria. None of us have been sick except for a cold. I haven't seen my family doctor in over 4 years so as far as bacteria is concerned, I don't worry about it. Keeping you water hot is the most costly thing in your home, even more than your refrigerator. Think of it this way by lowering your water heater you are not only saving money but helping the environment, too.

    Bookmark   March 23, 2009 at 8:34AM
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A water heater really can get contaminated if the setting is too low. My parents had that happen some years ago. Dad dropped the setting on their second heater for the bathrooms. I don't recall how low it had been set. The hot water developed a foul odor. This is city-treated water, not a private well. The tank had to be drained and flushed. The problem had to be related to the low temperature. The heater for the kitchen/laundry area hadn't been reduced in temp, wasn't affected, and is on the same water supply. The temp was raised accordingly and the problem hasn't recurred.

    Bookmark   March 23, 2009 at 3:26PM
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Rachal, most reputable sources I've seen maintain that hot water is not essential for sanitary hand washing. The use of soap and the friction of vigorously washing for a minimum of 15+ seconds is far more important that hot water. Warm water is more of a comfort factor. In order to sanitize in water, you need far hotter water than the hands could stand. The use of alcohol based sanitizers after proper washing would not be necessary, although it sounds like you don't wash your hands, only use a sanitizer. If so, well, it's better than nothing provided you're scrubbing the hands for the proper time. And although it's a sore topic with some people, the antibacterial soaps are helpful too.

    Bookmark   March 23, 2009 at 6:12PM
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A few years back I turned the temp. on my electric hot water heater down to 120Ì. And a short time after I did we noticed we had a problem with our dishwasher. When we were putting away the clean dishes we would notice un-disolved dishwasher detergent on the dishes. So we would have to run them through another cycle. this went on for a couple of weeks and then I realized what was going on. The water wasn't hot enough to disolve the detergent. I raised the temp. back up to 135Ì and everything went back to normal.

I realize this is the Laundry Forum but you have to think beyond laundry.

    Bookmark   March 24, 2009 at 12:58PM
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Actually, turning it down too low can lead to the growth of Legionella pneumophila, the bug behind Legionnaires Disease. The article below gives all the details, but here's the summary:

* 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

Here is a link that might be useful: Article from Treehugger

    Bookmark   March 24, 2009 at 5:38PM
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