How long should a normal 50 gallon hot water heater typically last hot?

My hot water heater keeps shutting off (thermocouple stuff). I'm not worried about fixing that so this question isn't about that.
Once I turn on the hot water heater, and then shut it off after about 15 minutes which is all it takes to heat the water, how LONG should the water STAY hot inside the water heater?
The heater has no extra jacket but it's cool to the touch. Assume the temperature outside ambient is about 75 degrees F. (The point is that it's warm at this time of year.)
If I take a shower in the morning after the heater shuts down at night with no water running, the water is too cold for a comfortable shower.
Just curious how LONG the water should STAY hot assuming no water flow, 135 degrees F setting, normal 50 gallon hot water heater, normal 75 degree F ambient temperature?
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On 9/2/18 1:23 AM, K120 wrote:

135 degrees F is way too hot. We're talking scald city, not to mention wasting fuel. 120 is the recommended temp.
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On 9/2/2018 6:07 AM, Wade Garrett wrote:

  For washing and showering 120° is just fine - my main heater is set at about 125° . However , for the dishwasher , it needs to be around 140° ... so I added an auxiliary point of use heater under the kitchen in the "crawl" space . As far as the OP's original question , a year or so back I went to Memphis for a few days to have a roof put on our house there . The day before I left we had a several-hour outage , so I turned the breaker off while the generator was running - and forgot to turn it back on . The wife said the first 3 days she still had "hot enough" water for a decent shower , but by day 4 it was a "just warm" and by day 5 it was "cold"shower time . I don't know how long it would have stayed hot if there was no usage ... BTW , this is an electric unit , the OP's is gas - with that tube up the center it's got to cool off faster than an electric .
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On 9/2/18 9:05 AM, Terry Coombs wrote:

My Bosch dishwasher features a built-in water heater element that can raise the wash and/or rinse water temp to whatever I want.
I don't use it though as the standard 120 degree water temp from the house's water heater does fine.
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On 9/2/2018 8:56 AM, Wade Garrett wrote:

  120° is not hot enough to sanitize . Part of the reason I put the POU unit in is because it took over a minute to get hot water to the sink/DW - one of the pitfalls of using 3/4" pipe all the way . It only steps to 1/2" just under the floor where the pipes enter the living space . But we also don't get reduced flow to the shower when you flush the toilet ...
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Thank you for that information that the water can stay hot for days. That's exactly what I would have thought.
You're right that this is gas fired where the centerpipe is a loss that can't be insulated against since it goes up to the roof (I guess).
I forgot to mention the incoming water temperature, which is a comfortable temperature for washing hands but not for a body.
The temperature overnight is about half way (give or take) between hot and the cold water incoming temperature.
I haven't actually measured any temperature with a thermometer though. I was just asking how long a normal heater would stay warm.
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On 09/02/2018 06:07 AM, Wade Garrett wrote:
[snip]

Never heard of mixing hot and cold to get the right temperature?
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On 9/2/2018 11:12 AM, Sam E wrote:

Sure, but many young kids and seniors have been scalded because they don't realize what is happening.
Mine is about 128 at the kitchen faucet. The DW will boost temperature to sanitize.
http://www.eemax.com/2015/12/07/6-important-safety-facts-regarding-hot-water-scalds-and-burn-injuries/
https://injuryprevention.bmj.com/content/4/3/238 Abstract Tap water scald burns account for 7% to 17% of all childhood scald burns that require hospitalization. Often the burns are severe and disabling. Toddlers and preschool children are the most frequent victims. In 45% of the injuries, the unsupervised victim or a peer turned on the tap water; in 28% the cause was abuse. Eighty per cent of the homes tested had unsafe bathtub water temperatures of 54°C (130°F) or greater, exposing the occupants to the risk of full thickness scalds with 30 second exposure to hot water. Such burns may be prevented passively by limiting household water temperatures to less than 52°C (125°F). New water heaters could be preset at this temperature and families could be taught to turn down the temperature on existing units.
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I was just asking how long a normal heater holds the hot water.
Scalding is so far out of the question that it's a non issue.
The setting is at 135 but the water isn't anywhere near that.
It's hot but not hot enough to burn anyone, not even a baby.
I was just asking how long a normal heater holds the hot water.
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On Sunday, September 2, 2018 at 1:23:14 AM UTC-4, K120 wrote:

It's too cold at the start of your shower or too cold at the end of a 20 minute shower? If it's the latter, the WH is probably OK. If it's the former, something is wrong. I'd suspect a broke off dip tube inside, so that instead of water going into the bottom of the tank, it's going into the top where the hot water exits. Tanks don't cool off that quickly.
As a test, in the morning after it's been shut off overnight, you could turn off the cold water coming into the tank, open a hot water faucet and draw water into a bucket from the drain valve. See how hot that water is versus water you get from the faucet under the same conditions.

In my experience you'd still have usable hot water for at least 24 hours, enough to be able to take at least a decent shower or two, where you economized on usage. You might have to use just the hot water though, ie not mix it, particularly near the end.
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said:

The start of the shower and the end of the shower in all cases is the same temperature (I don't measure it so this is just from taking a shower).
If the water is hot, it is hot enough for the entire shower. If the water is cooler, it's cooler for the entire shower.
The only temperature differences is in the first minute or two that it takes the warm water to get to the shower head from the hotwater heater.

I don't actually suspect anything is wrong other than the thermocouple. The only thing that is "broken" is the pilot flame goes out. But I know how to fix that so I'm not asking about that problem.
I'm just asking how long hot water normally stays hot.
The only cooling mechanism I can visually see and touch are the pipes and the water jacket and the ambient air. But if hot water isn't being used in the house, then it seems that ALL the hot water is in the tank itself.
I expect the hot water that is stagnent in the pipes inside the walls to cool down so I'm only talking about the water temperature at the shower after about two minutes of running the water.
It takes about two minutes (or so) for the hot water to get from the hotwater tank to the shower head.
Is that time about right for you?

This is a good test of the hot water at the faucet vs the hot water at the bottom of the tank. I haven't actually measured anything yet but I have cooking thermometers which should be able to give me an idea.
I was just wondering how long a hot water tank SHOULD hold hot water.
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On Sunday, September 2, 2018 at 3:48:36 PM UTC-4, K120 wrote:

And I'm telling you if the water heater is operating and you turn it off at 11PM and by 8AM the next morning there isn't enough hot water to take a shower, something is broken or hooked up wrong.

That depends on how long the pipe runs are and what diameter pipes. If the water heater is close to the shower, hot water can be there in seconds, if it's 70 ft away and two stories up, using 3/4" pipe and a low flow head, it can take many minutes. It is whatever it is.

A lot longer than yours is.
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said:

Thanks. Terry Coombs said essentially the same thing. The water in the hotwater tank, if not used, should stay hot for days.
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