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Hot water last long time everywhere but in my shower?

Hot water only lasts about 10 minutes in shower but lasts forever in kitchen and bathroom sinks!

How can I fix this?

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    What kind of water heater do you have ? What kind of shower valve do you have ?
    – Alaska Man
    Feb 27 '20 at 20:31
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    Do you have more than one water heater?
    – Kris
    Feb 27 '20 at 21:59
  • Hello, and welcome to Home Improvement. Unfortunately, we'll need more info before we have any chance of helping you. Please take our tour so you'll know how best to participate here. Feb 28 '20 at 13:17
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Unless something is badly broken in your setup, the most effective fixes are (1) installing a flow restrictor, (2) increasing your water tank size, and (3) raising your water heater temperature.

You're probably just using up all the hot water in the tank. You can confirm this if you have a 5 gallon bucket (you can get one for a few bucks in my neighborhood big box store). Stick it under your shower head and see how long it takes to fill halfway. A modern shower head will take about a minute to fill 2.5 gallons, which if it's 80% hot water and 20% cold, means you're using 2 GPM hot water. If you have a smaller 40 gal tank, you have 20 minutes of shower. But if you had an older shower head (probably your case), it could have easily have twice the flow, meaning you have 10 minutes.

You can lengthen your shower using any of the suggested techniques, the easiest and most effective being replacing your shower head. In many places, your utility will give you a water-efficient shower head for free.

My bathroom sink is 1.2 GPM, and most are similar, which would give you 40 min hot water in the same setup.

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  • This is interesting advice but may well be completely incompatible with the OP's house. Since he didn't even mention flow rates we don't know whether he's simply using up all the hot water, or (for example) his shower mixer valve is broken and internally rotates to cold. Feb 28 '20 at 18:10
  • Agreed there could be other stuff going wrong, but it would be pretty odd. 10 minutes is a likely threshold to expect a high-flow shower head to exhaust a typical residential water tank, and I'd find it fishy that a mixing valve would switch over to sending cold water after working fine for 10 minutes. That said, weirder things have happened, and OP could do other stuff to confirm (e.g. confirm that hot water is out house-wide once the shower runs cold).
    – Steven
    Feb 28 '20 at 20:05
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Sounds like the shower is using too much water in general. If you have a strong, powerful stream coming out of the shower head, it probably has its water restrictor removed, or its old enough to not have one. You might not be totally happy with the new spray, but a new shower head would use less water and therefore give a longer shower.

If the water is just getting warm after 10 minutes and not totally cold, then your single handle faucet might need some adjustment. Those can be set to use only a certain amount of hot water to control the max temp of the shower. If your hot water drops in temperature after a few minutes, your shower temp will drop, and you won'y be able to "turn it up" because it's already on max hot.

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Have you thought about a hot water mixing valve? It tempers the hot water coming out of your water heater with cold water to achieve the desired temp (recommend 120 degrees). Then you can turn up the tstats on the WH to 140 or 150 effectively increasing the "size" of the WH without actually replacing it.

Hot water mixing valve

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  • Tempering valves are definitely a good idea, but need to go at fixtures to be net beneficial (or at least, one-per-bathroom, located at the bathroom). A centrally located tempering valve is counterproductive, as it strains the booster heater in your dishwasher (or leaves you with lukewarm water for manual dishwashing, which can be worse), while allowing Legionella and friends to grow in the hot water piping still. Feb 28 '20 at 2:20
  • Thanks 3ph. I think I learn more than I contribute here! I understand why it's better to run the water heater hotter, but don't most people run them at 120 -125? What would be the difference between using a mixing valve at the WH to get to 120 degrees vs setting the WH tstat at 120? Don't get me wrong I like your comment, just trying to learn more. Feb 28 '20 at 15:32
  • Using a mixing valve lets you store the water at a higher temperature, which gives you a longer runtime (i.e. until the burner kicks in) for a given delivered temperature. This is especially helpful with heaters that can attain higher tank temps readily (gas tanks, EcoCutes, and indirects) Feb 29 '20 at 0:14
  • Thanks again, but that wasn't the question I intended to ask. In my answer I mentioned the same thing. What I was trying to ask was when it comes to hazards like Legionella what is the difference between a WH at 120 and a mixing valve at 120? Feb 29 '20 at 0:24
  • Ah! Having the WH at 120 means that the tank can breed Legionellae, while having the tank hot enough to kill the bacteria with a mixing valve at 120 keeps the bacteria from growing inside the tank at least. (In many residential environments, this is a semi-acceptable solution, as the piping system is limited in size, and dead leg control isn't an issue. Larger buildings tend to have more trouble with Legionella growing in hot water piping, as they simply have more of it to contend with.) Feb 29 '20 at 0:36
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It's your shower head

You have a high-flow shower head, which is basically dumping your entire hot water tank in minutes, wasting your limited time of water.

A low-flow head will perform much better for you.

Massive amounts of water coming down isn't a tenth as useful as people think it is.

Install 1-handle joystick style faucets for longer run

If all your house's faucets are the 1-handle joystick type with a thermostatic anti-scald feature, then you can crank the hot water heater temperature up to the max without worrying about scalding. This is a good idea anyway, given the several types of bacteria that can breed. and fester inside a water heater not kept hot enough (140F). A hotterhot water tank contains more energy, and when you meter it out for your target temperature, that means it lasts longer.

But don't get clever and think "ho ho, I don't need a fancy valve, I can avoid scalding just by using the faucets properly / pulling my hand out". Yeah, no... if that worked, they wouldn't require anti-scald valves, would they!

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