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My shower runs out of hot water quickly. Initially the water is perfectly hot, then it starts cooling after a minute or so and we need to adjust the lever to maintain the temperature. Somewhere around 10mins (give or take) you're pretty much out of hot water. I've tested this in our other shower as well, same issue.

To troubleshoot, we bought a new Rheem 50 Gal Gas WH as the previous was 12yrs old. Its only my wife and I in the house and we never shower at the same time in different showers.

There is no mixing valve in my setup as far as I can see, I've traced the hot water pipe from the WH to where it exits the basement.

To troubleshoot, I've been in the shower, waited for the water to start cooling, then ran downstairs to run the kitchen sink hot water and the water was noticeably cooler as well, similar to what I was getting in the shower.

Any ideas? New WH(same issue present w/ old WH), no mixing valve, water heater is set to a notch (or 2) above the default setting.

I have an HVAC friend as well as an HVAC uncle whos been in business for a while and he doesnt have a definitive answer either.

The basement is heated, so its usually about 68F-70F.

  • I would have thought sediment in the tank, but since you have a new WH, kinda throws that out the window :D – Pᴀᴜʟsᴛᴇʀ2 Feb 19 '15 at 1:57
  • How new is your shower? Some shower fixtures have internal mixing valves. If it does it could be your issue. – Mnc123 Feb 19 '15 at 2:09
  • What temperature do you have your hot water tank set at? – Steven Feb 19 '15 at 2:24
  • There is nothing wrong with the showers. The issue is with your tank and we need more info on that. – DMoore Feb 19 '15 at 5:14
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    Have you seen this other Q&A: diy.stackexchange.com/questions/9105/…? Do any of the posts there help you? If they do, please let us know so we can mark this as a duplicate. Thanks! – Niall C. Feb 19 '15 at 20:06
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Replacing the tank eliminates the most common suspects, although it is conceivably possible that you've just had terrible luck and there's a similar issue with the new tank as well. You can test the capacity of your water heater using this procedure, filling buckets with hot water and measuring the temperature to see how much you can draw down before it gets cold.

Assuming the tank capacity is fine, then the remaining possibilities are that the hot water can't get to you (which seems quite unlikely when there's no tempering valve), or that you are simply using it all up. If your shower heads have really high flow rates (like >5GPM), it is possible you could actually be using up all of your hot water in just 10 minutes. You can measure the flow rate of your shower head by using the bucket from the capacity test and timing how long it takes to fill it.

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I would check for a damaged dip tube on the cold water inlet. I would wager the installer melted it.

  • Why do you suspect the installer melted the dip tube? What actions could the installer have taken, that would have caused that? Why would a melted dip tube lead to the symptoms described in the question? – Tester101 Dec 11 '15 at 13:23

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