Had our gas water heater replaced after it let go at the beginning of January. I had a 50 gallon, 40,000 BTU Rheem unit fitted. The guy set the thermostat to "A", which according to the manual, should have the water at approximately 130°F. All I can say is that using that setting the water freakin' hot compared with the old unit.

I dug out my pyrometer and found that the hot water in the closest bathroom to the heater was running at 134°F. Hmm. With measurement errors I'm not sure that what the pyrometer is saying is that far out of line with the thermostat. But, I still felt that the water was too hot, so I turned the stat down a bit. This lowered the temperature in the near bathroom to 129°F.

Just for completeness, I measured the temperature in the more far flung parts of the house. The longest run to the kitchen showed 120°F, with the upstairs bathroom at the back of the house reading 123°F.

What do you run your water at?

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Release the Kraken

120 degrees was the standard unless it's changed. The shower's have scald guard protection so you don't get burned by them. Faucets and tubs are the only danger for children. 120 degrees shouldn't be a danger for anyone but hot enough to be comfortable.

My son has always had his dangerously hot. I tried to get him to turn it down for years but he refused. My grandson is now 6 and they've finally turned it down. I wonder if there was a scalding I was never told about?

I think my HW tank is set for 140º. Haven't actually measured the output at any of the faucets, but it's a small house and the runs are fairly short.

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"I drank WHAT?" (Socrates)

My hew tankless is set at 120 and that is just right.

Mine is electric. I have to keep it at 120 or the breaker pops. I'd rather have it at 140.

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No baby we aint

In my last home (very large home) we had a 100 gallon "Super Store Tank" which is basically a non powered, super insulated giant thermos bottle to store hot water. The water was heated up by the gas fired boiler and then stored in the Super Store tank. Because of the very real threat of Legionaries Disease living in a tank, I set the super store temperature to 145ºF at which all traces of Legionaries dies. Since we had no young kids at home, the high temperature was no danger and in all the showers were thermostatically controlled shower body valves that kept the water temperature from fluctuating when someone else in the house turned on or off the hot water.

In our current home, we no longer have a hot water tank and there is no stored hot water. Instead we have a Rannai wall mounted instant and endless gas fired water heater. Since the unit stores no hot water at all, there is no reason to worry about tainted water. That unit is set to 120ºF and supplies us with endless hot water on demand.

BTW, anyone who is in the market for a new hot water unit, might want to look into the Rannai tankless hot water heater system. Not only does it work great, the unit is only about 15" wide x 25" high and stands off the wall around 10". They say if properly maintained (flushed out yearly - takes 1/2 hour to do) the unit should last well over 20+ years. I also love the fact that there is no hot water tank taking up space, developing leaks and getting in my way in our garage.

20 year old gas 40 gallon tank set at "A" Which is just right according to Goldie Locks. That was 133* F at the kitchen faucet. I think I'll turn it down a little bit, but from previous experience very much and the stat sticks off. Momma Bear gets grumpy if she has to take a cool let alone cold shower!

Ivan

When my bathroom mirrors fog up and the hallway smoke detecter goes off;

I turn down the water temperature, until Spring comes back.

Tank less water heater are ok unless you live ware it gets really cold.
My 75 gallon water gas heater does not come on that often and does fine if I clean it once a year.
4 gallons of vinegar helps with the hard water we have here...

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Only difference Fool/Mule-ears

I have mine set at, when it gets up to the second floor, "darn hot" as measured by the finger under the tap test. Don't use "as is" except for shaving.

Yes, it's visitors and children that concern me, too. I get that having hotter water means that less hot has to be mixed with the cold to get a good shower, and the tank is less likely to be drained by successive users. As 99% of the time it's just my wife and I here, I'll keep the stat turned down and save a bit on my natural gas bill. The water is still hotter than the old setup.

As set up by the installer, the water in my downstairs bathroom it seemed crazy hot to me. The instruction booklet showed how long it takes to cause a major burn at the different temperatures. The time drastically increases as you get down to 120°F or less. Conversely, for a temperature increase from 130°F to 135°F, the burn time got scary short.

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Release the Kraken

For me,, there are two temperatures to think about.

1) Threshold of pain that ends up being 107 degrees F

2) Minimum domestic hot water temperature is 120 degrees F due to bacteria growth.

So, based on those two temps, we keep our water heater set at 122 degrees F

At 122,, it takes more than 3 or four seconds to be REAL uncomfortable in the shower.
That is long enough to adjust the temp, or get out of the way.

The other reason to keep the temp low is that it saves LOTS of $$$$,,

My thoughts exactly. You're going to have to mix in cold water anyway to bathe or shower so why heat it higher than necessary when not in use.

Maybe someone in the know will explain the need for the wide variance in temp settings on a water heater.

We have had a gas tankless hot water heater for about 10 years. It is a big money saver. Set at 130 degrees. That way our shower mixes enough cold water with the hot to have a comfortable shower without running the heater full blast and wasting gas.

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Can my S&W Mdl 10 shoot +P

As previously stated 120° is the minimum temperature to prevent legionella. I keep mine at 130° to be safe. Legionella is nothing to mess with!

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Dennis
SWCA #2409, SWHF #353

140 used to be the standard but a lawsuit in which a immigrant left her child in the tub and answered the door left the child with burns and webbed feet. Now 130 is the standard. Mine runs about 125 in a 50 gallon tank.

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Front sight and squeeze

120 makes a good breeding ground for bacteria. I turned my water heater up to about 150. My skivvies are whiter now.

I do my dishes by hand with only hot water. They come clean and dry quickly.

Webbed feet?

125F on mine, but there are no children in the house. It’s really easy to change, too.

My electric does 145 deg F in summer, heating system boiler with a water coil does 185 deg F in winter. No kids, no problem.

My shower on full hot is too hot. That's all I know.

I too have a Rinnai, set at 120⁰. Provides all the continuous hot need. Electric dishwasher heats water to 150⁰ for additional protection aginst bacteria.

I have my AO Smith tankless heater set at 135.

I have not checked the actual temperature at a faucet, but it's hot.

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BTDT, Got The T-Shirt

I keep mine set low enough that I don’t need any cold water mixed in when I shower. Keeps the bills down. I live solo so get no argument from anybody about water temp. Wouldn’t be worth throwing (a spouse) to save a few bucks of heating bills it I were in that position, I guess.

The real risks of high temps come with kids and the elderly. Your circumstances will dictate the analysis leading to a reasonable answer. As you can tell, there are a lot of variables to consider.

I prosecuted a case about 12 years ago in which a "Dad" bathed a young boy in water far too hot. The background of the pathological relationship of the parents was the main issue, but Dad held the screaming kid in the far too hot water until he had terrible burns. That is likely similar to the comment about webbed feet. I can still remember the sentencing hearing - the inmates in the court room waiting for their cases heard the facts and were giving the offender really hateful glares. I suspect they imposed some street justice.

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NHI, 10-8.

Mine is set to whatever the dishwasher says is needed to sanitize the dishes. Memory tells me it is 140

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Pete
I ain't no fortunate son

I have a temperature sensor mounted and insulated on the outlet of my water heater and I get 133 degrees there. Plenty warm enough for my needs. As far as the tankless heaters, I went to a service class for Rinnau and the necessary water flow was a turn off for me. Also I found out they were not honoring their warranty on the heat exchangers even though many of them were installed with the necessary manifold for chemical cleaning. (I learned this from my local Johnstone Supply about a half year later.) I hope this policy has been updated. Some of the other operating controls were a turn off for that brand. Water flow was a main issue. I don’t know about the other brands. If I had a tankless heater in my house I would go all out and install a holding tank with circulating pump, only because I can. (Pump between the heater and tank like commercial buildings most all have.) I hope things got better with the tankless heater operations.

I always feel that the American hot water systems are lower in temperature than here in Kiwiland. But then I have only used hotel/motel bathrooms situated who nows how far from the hot water source and set who knows where on the temperature dial.

Recommended maximum hot water temperature here is 50-55 C, or 122 - 131 F. We run a natural gas Infinity hot water heater situated just outside our bathroom window, and the bath temperature at 55 C is too hot to just climb into it. Even the shower needs the mixer turned towards the "cold" side a bit.

American hotel baths and showers are more at the top end of "warm" for me.

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View from down under

120 is hot enough to prevent bacterial growth. Assuming your incoming water has been properly treated it's enough. If you're on untreated water you may want to set it at 140 or higher which is hot enough to not just prevent growth but to kill any bacteria present.

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Or something like that . . .

My WH is set at 120 degrees. Not sure what the actual temp is at the faucet, but it’s hot enough for bathing, laundry and the dishwasher.

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213th FBINA

That's a good point. Is the main concern the temperature in the heater, or the water in the whole system?

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Release the Kraken

From the DOE.

I'll err on the side of caution and set my water heater for volcano (acutally 150).

Can you get it in a "Lost in Space" version like the one that came with the lunchbox I had in 3rd grade?

Rennai tankless set at 120 by the plumbers has been good for almost 7 years now. Flushed every year.

Per the lawsuit the kids feet were permanently disfigured with skin on the toes all adhering to each other. This lawsuit resulted in the American Gas Association changing the max temp available on a water heater from 160 to 140 and the recommended from 140 to 130.
AGA made sure that all it's member utilities knew the results, though they were not a party to the suit.

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Front sight and squeeze

My five year old water heater can get much hotter than 140.

Temp of my freshly brewed coffee is 160 degrees. While water straight out my gas water heater 125 degrees.

We like 128F. Longest runs are still darn hot without being obnoxious.

Anyone with a hot water tank in their home SHOULD look up Legionnaires Disease breeding and living in hot water storage tanks. It is a real situation!

Have not measured the temp, but my latest Southwest Gas bill is double what it was last year. I'm turning it down!

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I used to be disgusted..

I have an 81 gallon water heater set at 130°.

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Music/Sports/Beer fan

I NEVER give out personal data like that on the net!

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Regards,
Lee Jarrett

All opinions with no real solution IMO.

Where do you live? Alaska? Florida? Chile?

What describes your home? Rancher? Two-Story? Mansion?

Where's the water heater located in relation to sinks or bath?

Water doesn't stay hot in your pipes after turning off a faucet or shower. The longer the distance the longer it takes to replace that water with hot water.

If I remember correctly even a Rinnai tankless water heater doesn't solve every issue. Sure it offers endless hot water but you still have to replace what's already in the pipes. I believe you have to install something under sinks or elsewhere to get "instant" hot water everywhere.

Doesn't matter what temp I set my heater at. All I know is in the Winter it takes a little longer to get a good temp in the shower because the water pipes are colder. Sounds stupid but I believe some heat is lost through the cold pipes as they absorb heat from the water.

If you do a Google search, you will see that 140ºF is the minimum temperature that Legionaries no longer lives, not 120ºF. That is why 145ºF is where I used to set it when I had a water tank. 120ºF will not fully and reliably kill Legionnaires. If you are concerned about scalding, install a mixing valve after the hot water heater or tank.

In review:

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Music/Sports/Beer fan

Not stupid, basic thermodynamics.