What are the Safest Temperature Settings for a Hot Water Heater?

Tricia Christensen
Tricia Christensen

One can practice both safety and economy by keeping water temperature at doctor approved levels. Very hot water temperature can cause burns with great rapidity, and as such, care in setting your hot water heater is required. Setting the hot water temperature lower also means a savings in energy bills for heating the home's water in many cases. However, a lower temperature does mean you will run out of hot water more quickly.

A water heater should not be set beyond 125 degrees Fahrenheit.
A water heater should not be set beyond 125 degrees Fahrenheit.

Most experts recommend that hot water temperature should not exceed 125° F (51.66° C). A water temperature exceeding this poses serious risk of bad burns, particularly to children. In fact even at 125° F, if the child puts his or her hand in the water continuously for two minutes he or she may get second or third degree burns.

As temperatures over 125 degree fahrenheit can burn both children and adults quickly and severely, boilers must be locked at lower settings.
As temperatures over 125 degree fahrenheit can burn both children and adults quickly and severely, boilers must be locked at lower settings.

Some pediatricians instead suggest setting the hot water temperature at 120° F (48.88° C). With this water temperature, a child would have to run water over the same place for ten minutes prior to receiving a severe burn.

Some pediatricians suggest 120 degrees is the hottest water should be in homes with small children.
Some pediatricians suggest 120 degrees is the hottest water should be in homes with small children.

Temperatures higher than 125° F can burn a child, or an adult quite severely, and quite quickly. For example, it is estimated that it takes only two seconds of exposure to water at 150° F (65.55° C) and only six seconds of exposure to water at 140° F (60° C) to cause a very bad burn to a child.

Two seconds of exposure to water at 150 degrees will severely burn a child.
Two seconds of exposure to water at 150 degrees will severely burn a child.

Some are concerned that lowering the water temperature will result in soap working improperly in dishwashers or washing machines. Actually most soap and detergent is meant to work at between 120° to 125° F. Thus soap is actually designed for this temperature.

Others are concerned that lowering water temperature might lead to greater chances of passing illness between family members. Actually, the best method for preventing illnesses is handwashing with warm, not hot, soapy water. 120° F water is quite hot enough to wash most germs away. It will not always work, since some germs are airborne and one contracts them through exposure or inhalation of the infected droplets of someone else, as after a sneeze.

In terms of cost saving, dropping the water temperature setting by ten degrees typically saves approximately 4% on one’s cost to heat water each year. This can make a profound difference if dropping the water temperature from 150° to 120° F, saving essentially 12% a year.

Temperatures higher than 125 degrees can burn a child in the bath.
Temperatures higher than 125 degrees can burn a child in the bath.
Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent wiseGEEK contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

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Discussion Comments


Our manager's daughter was in the tub and just reached suddenly and turned on the hot alone. She suffered third degree burns on her legs, was in the burn unit, and suffered through skin grafts after that. Don't put the water temp over 125. It's a disaster waiting to happen at 140 or 150!

For the person with the hotel - you need two hot water tanks for that many people!


The "safest" temperature is that temperature which kills germs with the aid of soap/detergent, and is not so hot as to scald a person before they have time to react. Period.


Nobody jumps into the water heater tank. What the temp is in the tank is much hotter than what you use at the tap. If a child gets into a bath that is too hot, then the parent screwed up by not supervising when the tub was filled.

The water is not170 degrees when it hits your skin unless you turn on the hot tap only and let it get really hot before you jump in. That is absurd. Everyone adjusts the temp of the water using both hot and cold faucets before getting in the tub or shower.


I opened up the door where our water heater is at and so much hot air came rushing out. I don't think it's very safe to have it as hot as it is.


Its true that having a moderate water heater temperature can save you money in your home. It's also true that over time water heaters lose their efficiency. Replacing your water heater can actually save you money.


You don't need to set the temp high enough to kill legionella. At 123 F legionella will not grow. If you set the heater to 140 F after installation and leave it there for an hour, you can then turn it down to 123 F.


To say the water should be set no lower than 140 degrees to avoid legionarres is absolutely *crazy*!!!!! You're going to find some child with terrible burns if s/he hits the tap anywhere near that temp.


Every water heater is preset in America to 120F by the manufactures, but some states like Wisconsin require the water heater temp to be at least 125F. I set mine at 125F, which is the recommended setting for my REEM water heater. It all depends though, on the size of your water heater and the number of machines using your water heater, as well. I find setting it below 115F is way too low, because by the time the water reaches my shower on the other side of the house, it's already cooled off a good 10 or more degrees. And if the dishwasher or washing machine are running, it cools the water temp even more to the point where sometimes I find myself taking a lukewarm shower. So, setting mine to 125F seemed to do the trick.

But it varies according to the size of the hot water tank, the size of your home and the number of machines you have that use that hot water tank in your home as well. Set your water temp to what you feel is adequate to your personal needs.


Water heating requires a minimum supply temperature of 140 degree F to mitigate the presence of legionella bacteria which causes Legionnaires disease through inhalation of bacteria- laden water (i.e., steam mist from a shower).

Having the temperature lower than 140 in water heaters is dangerous. You can always add a mixing valve (to mix the hot water with cold water) to reduce the temperature below 140 F.


Most dishwashers heat the water internally using electricity, so the argument that the water coming from the pipe is not hot enough holds no water.


I think the hot water temperature problem at a large institution is more of a heat recovery situation than a thermostat setting problem. If I only have a hot water tank that holds 200 gallons, for example, there's every chance the fifth or sixth bather is going to get nothing but cold water. The tank hasn't had time to heat the incoming water, and it wouldn't matter if I set the thermostat to 120 degrees or an insane 200 degrees-- there's only a finite amount of water that a traditional hot water tank can process.

My suggestion for hotels with numerous guest rooms and a limited hot water supply would be to install individual hot-water-on-demand units in every room. It might be a significant investment up front, and maintenance on those kind of units can be more expensive than traditional hot water tanks, but at least customer no. 7 won't have to suffer because customers one through six beat him or her to the shower in the morning.

It may not be the best solution for a private home (just invest in a larger traditional tank), but in a situation where customer satisfaction is a high priority, modern heat-on-demand units set at a child-safe temperature could prevent further problems with room refunds and angry phone calls to the front desk.


I just stayed at a high end hotel on the coast where the water was really hot! When checking out I mentioned it to the desk clerk and asked if she knew what the temperature was. She readily responded, "175 degrees. Our guests do not like cold water". There is a spa and a kitchen in the condo. Isn't that temp a lawsuit waiting to happen?


i work for a hotel that has 70 rooms. i set the temp to 130 and after five or six rooms of use, the water goes cold, leaving the others without hot water and me with having to refund room stays! what is the ideal temp for a hotel this size, that on average, houses 10 to 30 rooms daily. with two to four guests per room.


So call a professional. Don't make a simple question complicated. A typical hot water shower temperature needed in summer is 65 F or less and roughly 75 F in cold winter. Safe temperatures won't damage your skin in the long haul, plus they save energy.


here you go. #7 5 and 3 are missing the point. you can shower with anti-bacterial soap. but what about the walls and tub bottom? are they sanitized before you enter to shower? same with the bathroom floor and everything else in your home and all homes, so don't feel i disrespected either of you. it was not my intention.

i was in the appliance repair business for 40 years as a technician and then owner tech. legionnaires was caused by bacteria in the drain line from a combination of dust water which creates a slime very much like snot. pull out the drip tray under your refrigerator and you will see brown stains, maybe water, and sometimes a greenish substance. this occurs because when your fridge defrosts the water goes down a tube to the drip tray which is then evaporated by the condenser fan, which has dust all over it and sits right next to the condenser coils which removes heat from the refrigerant which draws the heat from the evaporator coil in your freezer. this is the basics of how a refrigerator works.

to sum it up, you have a warm condenser coil trying to be cooled by a condenser fan which blows air through your dirty condenser into your kitchen. that's why you feel warmth on you feet, also why your dog and cat love to lie in front of it in the winter. this adds dander to the drip tray to boot. presto! you have the perfect formula for air borne legionnaires disease.

i always tell mothers of toddlers to clean the drip pan at least once a month to prevent diseases from affecting their babies, or at least cut down a dangerous situation. so carry water with you so you needn't use a water fountain, and whatever germs are out there at least you restricted one. unless you go visiting and sit in the kitchen. every person that dies (excepting drive bys and tragedy) dies from (help me with this) pneumonia because the weakened body cannot fight that germ. it's true, all of it is true. okay, how'd i do #7?


my word! #4 if you let 170 degree water hit a metal pan for a few minutes you could fry an egg. Set the water 120-130 and add cold water as needed. if you have hard water and your dishwasher leaves spots push the button for high temp. wash and it will do the trick. 140 and above settings are a waste of oil to me.

our heater comes on 30-45 seconds after we turn on hot water and shuts off seconds after we shut water off. someone shut the heater off and nobody noticed for almost three days. we had a electric heater (also known as the silent thief) which wasn't bad when energy was cheap. our bill went up every couple of months. when it blew i called our oil co. got a discount for paying the same day had hot water since 5 p.m. that day and every day since. our electric bill went to half of what it was.


Why is the recommended setting 120 degrees when other articles state that you need at least 130 degrees to kill dust mites in the wash?


My wonderful plumber advises we set the hot water tank to 130 degrees. He says that there is always a dip in temperature before the tank thermostat calls for more heating, and if you set at 120 degrees, your tank is cycling below 120, and you risk having bacteria colonize the tanks. Legionella is the big concern here, and note that babies, the elderly, and the immunocompromised (chronically ill, cancer patients) are more vulnerable to Legionella than the rest of us. If you are concerned about energy costs, you can go to a smaller but more efficient tank system. But don't drop the temp to save money.


Too many people seem to be thinking that the ideal water temperature is what you measure as it comes out of the tap before any mixing with cold water. This is wrong.

Hot water is meant to be stored at a high enough temperature to kill off legionella (70C or slightly higher). Mixing this hot water with cold (ideally through a thermostatic tap will produce the ideal temperature for a shower or bath, without risk of scalding (set to your choice) and without risk of catching legionnaires disease when taking a shower (most common way - breathing in water vapour / droplets). It need not cost more to store water at this higher temperature, you just need extra tank insulation to the standard, say six inches thick or more - and it will keep hot all day if using overnight cheap rate electricity.

Domestic hot water systems were never designed to operate at "usable" temperatures, but to be mixed with a cold water supply to achieve the optimum usable temperature, which needs to vary according to what it is to be used for.


I tried to wash my hands at my daughter's school but the water was very hot. I told the school staff and was told that the water had to be at 102 degrees by state law and nothing was done. Water at 102 is not that hot, so clearly the water temp at the school is over 102. How can I make the school track the temp that comes out of the tap?


The reason you can stand a hotter temperature in the shower, is that, you aren't. The shower head, in breaking up a single stream of water into many tiny streams, greatly increases the surface area of the water. Heat transfer happens at the surface, so the individual tiny streams cool much faster as they travel through the air, than a single, thick stream would.

So the water has cooled to a tolerable temperature before it hits your skin.


Seems to me that if you're stupid enough to turn on the hot water and only the hot water, you should get burned.


There's probably a better chance of getting burned from water hotter than 125 degrees than from getting a Legionellae infection. Lower the temperature and use a thermometer to check it. Anything between 120 and 125 F is probably good.


my daughter jumped in a boiling hot bath and had second degree burns to her feet. i am trying to find out if there is a health and safety law that all council/rented homes have to have a thermostat to control hot water temperature as i don't have one and the water is boiling. if anyone can advise me on this i would be very grateful. thanks.


My temperature knob fell off my hot water heater pilot lights, but not the burner. Help!


Does installing a hot water circulation pump have an effect on the warranty for the hot water heater?


I use a meat thermometer to check water temperature. Just run the water until the temperature is stabilized, tweak the thermostat up or down if needed, then check again a few hours later.

Household dishwashers rely on the detergent to clean and sanitize. To sanitize like a commercial dishwasher takes a much higher temperature than can be used with a dishwasher.


why is temperature of water 30 degrees cooler at shower/tube than the sink?


Temp tips on no. 5: 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.


how do i keep sulphur from getting into the hot water tank? my dad isn't living at his place and i have to keep draining the tank to get the sulphur smell out. any idea on how to keep this problem at bay?


I would like expert opinions for 5 (Roo69Ster) and 3 (anon28212)


Our plumber installed a new Thermostat in our domestic hot water tank in Feb this year. It burned out in July. A new one was fitted and plumber insists it is set to 60C. Water is too hot for safety.

He quotes Legionnaire's disease must be avoided with lower settings. We feel that this new unit may burn out also at this higher setting plus we can`t stand the heat of the water. Advise please, we are over 70 both my wife and I. JBB Troon


I currently have my heater set @ 120 F but am concerned about the possibility for bacterial growth/accumulation in the water heater and/or associated plumbing! I am comfortable with the hot water I currently receive and like the extra savings in electricity but I am ultimately responsible for any bacteria growth/accumulation *if* it does occur! What would YOU suggest? Thank you!


It seems that the suggested high temp setting is lower than the suggested temp for the rinse water for hand washing of dishes. I had previously been told that the optimum temp for the rinse water was 170F. Have I been told incorrectly?


I've heard that storing the water in the tank below 50 degrees C can allow some bacteria such as Legionnaires disease to survive.


i have a oil fired water heater. just had it serviced and now the water is very hot. checked the setting and found it on 120 can this thermostats go bad thanks?


The water heater at my mom's house has two settings that I see..."warm" and "hot". Where should it be? Between the two or closer to "warm" instead of "hot".

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