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Old 06-14-2012, 09:24 AM   #1
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Loss of hot water with increased demand


Problem: When one shower is being used and another person tries to use their shower, the hot water to the first shower is interupted for a couple of minutes.

Any ideas what is causing this? I have two water heaters which were set up in a series. One possible problem is the pipe which links the 2 heaters is 3/4" while the inlet and outlet pipes are 1".

Any ideas regarding what is causing this problem and how to solve it?

Thanks!

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Old 06-14-2012, 09:48 AM   #2
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Loss of hot water with increased demand


Is this a new install, or is it one that has been working ok in the past but has only recently started to fail?

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Old 06-14-2012, 01:34 PM   #3
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Loss of hot water with increased demand


We bought the house with this set-up. The problem has always been there.
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Old 06-14-2012, 03:16 PM   #4
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Loss of hot water with increased demand


Are there thermostatic mixers in the showers? Or one of them?
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Old 06-14-2012, 03:43 PM   #5
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Loss of hot water with increased demand


You should check the top elements in the water heaters to be sure they are coming on. The top elements are the quick recovery elements and are controlled by a separate thermostat than the bottom elements. Someone may have set the top thermostats way out of the park thinking that they are saving energy by not having them come on. With a high demand, you might be depending on the lower element only which cannot heat fast enough. Only one element at a time is ever heating, but which one determines where it heats in the tank, which is critical to satisfying demand. A 3/4" line is more than ample to supply two showers.
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Old 06-15-2012, 07:41 PM   #6
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Loss of hot water with increased demand


Quote:
Originally Posted by wkearney99 View Post
Are there thermostatic mixers in the showers? Or one of them?
no, not in either.
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Old 06-15-2012, 08:24 PM   #7
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Loss of hot water with increased demand


The anti scalds are built into the newer shower controls, so your not going to be able to see them.
I'd first be looking to see if they installed 3/4 supply lines all the way to the fixtures.
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Old 06-16-2012, 07:02 AM   #8
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Loss of hot water with increased demand


You definitely don't want a 3/4" hot line going from the water heater to the fixture. You'd have to run 2-1/2 times more water down the drain until you get hot water at the outlet and when you are finished, all the extra water that you've paid to heat is sitting there in that oversized pipe getting cold.
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Old 06-16-2012, 10:16 AM   #9
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Loss of hot water with increased demand


Quote:
Originally Posted by Maintenance 6 View Post
You should check the top elements in the water heaters to be sure they are coming on. The top elements are the quick recovery elements and are controlled by a separate thermostat than the bottom elements. Someone may have set the top thermostats way out of the park thinking that they are saving energy by not having them come on. With a high demand, you might be depending on the lower element only which cannot heat fast enough. Only one element at a time is ever heating, but which one determines where it heats in the tank, which is critical to satisfying demand. A 3/4" line is more than ample to supply two showers.
This won't do much until the tanks are repiped. They're piped in series, the first tank is doing almost all of the recovery unless the tanks are getting emptied. I doubt thats happening unless they're small. The OP problem was an interuption of hot water when the second shower is turned on, not running out of it.
To the OP: does it matter which shower is turned on first or is the same shower losing hot water no matter which one is turned on first?
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Old 06-16-2012, 11:29 AM   #10
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Loss of hot water with increased demand


I am going to throw this out there. What is the incoming water pressure to the house, and the water pressure coming out of the water tanks? Also, do you really need both tanks? What are the size of them, and how old are they? How large is the house? How many baths?
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Old 06-18-2012, 03:45 PM   #11
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Loss of hot water with increased demand


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This won't do much until the tanks are repiped. They're piped in series, the first tank is doing almost all of the recovery unless the tanks are getting emptied. I doubt thats happening unless they're small. The OP problem was an interuption of hot water when the second shower is turned on, not running out of it.
To the OP: does it matter which shower is turned on first or is the same shower losing hot water no matter which one is turned on first?
You assume that the first tank is doing the recovery. I'm assuming that neither tank is going into quick recovery mode or is set so low that the water is getting cold before the element kicks on. If the thermostats are not set up right or if elements are burned out, neither tank may be recovering quickly and that may be the cause of the interuption. With one shower running, the supply is sufficient. When the second shower is added, the supply of hot water dimishes and if the upper elements are not coming on, it is depending on the lower elements. Eventually, they catch up. I would check all of the thermostats and elements to be sure they set right and working.
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Old 06-18-2012, 07:36 PM   #12
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Loss of hot water with increased demand


And depending on the age and efficiency of the existing heaters you might want to consider whether replacing them with a single, more efficient unit might be a better solution. You might end up saving a lot more money in the long run.

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