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We have a new 60 Gallon (US) gas hot water tank. After running a bath, water coming out of it is warm instead of hot. Is this normal? Precisely, here is the experiment I performed:

  • Temperature outside hovering above freezing (not crazy cold for these parts)
  • Tank satisfied
  • Filled bath (hot and cold) to ~120L to get 109F bathing temperature
  • Drained bath (~2 minutes).
  • Filled again with just hot to ~100L and got 100F
  • Checked temperature of hot water running out of faucet now: 88F

Is this normal? Is there a better experiment to determine what is normal/ok?

Note: When tank is satisfied the water that first comes out of it is very hot (close to scalding).

Addendum: It's UG60-50MF1-N2U at https://giantinc.com/wp-content/uploads/docs/GI-FT-UG60ATM-En.pdf

Thank you!

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    The outdoor temperature isn't particularly pertinent unless the cold water source is a tank sitting outside at ambient. What is the cold water temperature entering the tank? What is the thermostat setting? What is the thermal output of the heater (BTUh or kW)?
    – Theodore
    Commented Feb 9, 2021 at 20:54
  • What is the tank temp set at? If it is only set to 120 or 130 you used more than 1/2 the volume it refilled with cold water lowering the temp in the tank so sure this sounds correct with the information provided.
    – Ed Beal
    Commented Feb 9, 2021 at 23:10
  • It is 50,000 BTU. I will measure the temperature of the water since the tank doesn't have an exact thermostat, but as I say, it's quite hot; almost scalding.
    – logidelic
    Commented Feb 9, 2021 at 23:59
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    60 gal at 50,000 BTU cannot fill a bath tub twice. Fill it once, then go time how long the burner is lit afterwards. That's how long you have to wait for the next bath. Which is probably less then the length of a bath. - "If you have a gas water heater, plan to wait 45 minutes for the water to get hot after the heater has drained its capacity. If you have an electric water heater, double that to 1.5 hours." – waterheaterhub.com
    – Mazura
    Commented Feb 10, 2021 at 0:35
  • Does the label on the water heater indicate the recovery rate? That's the specification you are looking for. Suggested reading: Residential Sizing.
    – HABO
    Commented Feb 10, 2021 at 16:31

3 Answers 3

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This is normal.

Your tank has 60 litres. You took 120 litres of cold+hot. So, let's assume you took 60 litres of hot and 60 litres of cold water. What went in? Cold water. Heating up this cold water will take time.

The only thing anormal, to me is :

We have a new 60L gas hot water tank.

That's small. Where do you live ? I live in a place with both abundant hydro electricity and abundant water, so a water heater would be more like 60 gallons.

After edits:

Is the dip tube installed correctly ?

https://www.discovercabrillo.com/what-is-a-dip-tube-in-a-hot-water-heater/#:~:text=A%20dip%20tube%20is%20a,the%20bottom%20near%20the%20burners.

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    Woah! I just edited my post. I meant 60 Gallons! Sorry about that!
    – logidelic
    Commented Feb 9, 2021 at 20:39
  • That changes things. Is the dip tube correctly installed ?
    – Jeffrey
    Commented Feb 9, 2021 at 20:42
  • I had suspected that the dip tube is broken and called the plumber who installed it to say so. They told me (without checking the unit) that me that what I was observing was totally normal and that it's working well. I have my doubts, hence my question. :)
    – logidelic
    Commented Feb 9, 2021 at 20:45
  • If the dip tube was broken or not installed the first bath would have run hot for a while then cooled off without the tank set point any guess is just that. What’s the recovery time?
    – Ed Beal
    Commented Feb 9, 2021 at 23:13
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    If the dip tube was broken you would get luke-warm water very soon after turning on the hot water because cold water entering the tank would be immediately mixed with all outgoing flow from the tank. This does not sound like your issue. Your issue is not an issue, it is normal. Commented Feb 10, 2021 at 6:08
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You've taken 26.4 gallons (first, 100 liter bath) out of your heater, followed immediately by 31.7 gallons (second, 120 liter bath) for a total of 58.1 gallons out of the 60 gallon capacity.

How long does it take to fill the tub, drain it, then fill it again, 10 minutes? You now expect to find that the 60 gallon heater is still full of full hot water? It takes time to heat water, even with a gas water heater.

If you really need to take 2 baths back to back like that (you really don't, do you, this was just an experiment, wasn't it?) you'll need to also install an on-demand water heater right after your brand spankin' new 60 gallon heater. That's probably the only way you'll add 40°F to water that quickly. The good news is that if you can find a gas-fired one, you'll already have all the gas plumbing right there, so you can easily plumb in the second heater so it's ready for the next time you need to non-real-world-situation stress test your hot water system.

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  • Except that those on-demand heaters do need a significant gas supply, so depending on gas piping, there may not be enough gas supply capacity at this location to feed both the normal water heater, as well as the on-demand. So there might need to be additional capacity added, or even a meter change out to a higher WC pressure, then pressure reducers at each appliance.
    – Milwrdfan
    Commented Feb 10, 2021 at 15:42
  • Good point, @Milwrdfan. I was hand-wavy and somewhat sarcastic with that suggestion. My main point is that you can't take 58 gallons out of a 60 gallon tank and still expect to get much in the way of hot water.
    – FreeMan
    Commented Feb 10, 2021 at 15:46
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As others pointed out - this seems to be nothing wrong with the tank, it's doing it's job as designed. A much cheaper solution than new on-demand tank heater would be to ask a plumber to install a mixing valve. You can then raise the temperature of the tank to let's say 140F and set the mixing valve to 120F giving you all the hot water you want.

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  • This isn't a bad idea, but it still won't provide "all the hot water you want". A somewhat lower water flow due to the mixing valve will slow the rate of water consumption, but it still won't guarantee "unlimited" supply. It will also cost more over time keeping 60 gallons at 140°F vs 120°F when the hotter temp isn't needed.
    – FreeMan
    Commented Feb 10, 2021 at 15:43
  • I agree. I exaggerated "all the hot water" part, and also agree on cost, however it would be pretty hard to calculate exactly when is the breakeven point in 140F in well insulated tank vs brand new on-demand. Interesting exercise though, if the OP wants to go through the calculation.
    – user129995
    Commented Feb 10, 2021 at 20:52

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