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Old 07-10-2012, 12:50 PM   #1
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Funky 2 water-heater configuration?


I have a two-story 3150 sq ft house, and the builder installed two gas water heaters in the attic, a 40-gal and a 50-gal. They are over 11 years old and are starting to fail. I cannot confirm whether they are installed in parallel, or as two separate systems that feed two independent hot water circuits. There is a common cold water pipe that connects both inlets, but the outlets of both run down into the subflooring (I can’t tell if they are tee’d together or not). However, something doesn’t add up right. To verify which fixtures are supplied by which tank, I turned off each heater one at a time and observed which fixtures stop flowing hot water. For the smaller heater, only about 5 fixtures shut off. But when turning off the larger heater, ALL the fixtures in the entire house stopped flowing hot water (and yes I did turn the small heater back on first). How could this be? Can anyone explain what could possibly be going on? Thanks!

Coy (League City, TX)

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Old 07-10-2012, 02:42 PM   #2
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Funky 2 water-heater configuration?


It sounds like the larger water heater supplies water to the smaller one.

When you say you turn off the water heater, are you just turning off the power and waiting for cold water or are you turning off the water supply? Each heater should have a manual valve on the cold water inlet side.

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Old 07-10-2012, 03:11 PM   #3
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Funky 2 water-heater configuration?


When I did the test, I turned off the cold water valve to each heater. Both heaters share a common cold water pipe (it tee's off to each inlet). But the outlet of both heaters just make a quick turn down into the subflooring, so I can't tell if they are tee'd back together or not (as would be expected for a parallel installation).
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Old 07-10-2012, 05:47 PM   #4
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Funky 2 water-heater configuration?


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Originally Posted by ckouba View Post
When I did the test, I turned off the cold water valve to each heater. Both heaters share a common cold water pipe (it tee's off to each inlet). But the outlet of both heaters just make a quick turn down into the subflooring, so I can't tell if they are tee'd back together or not (as would be expected for a parallel installation).
If they are parallel or series, you would probably tell by the piping above the floor. No reason for that kind of piping configuration to be below the heaters. Do you have a large tub that one heater could be feeding? Where were the 5 fixtures located?
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Old 07-11-2012, 12:40 AM   #5
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Funky 2 water-heater configuration?


All 5 fixtures fed by the small heater are closely located to each other in the house (so that makes sense).
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Old 07-11-2012, 12:41 AM   #6
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Funky 2 water-heater configuration?


So given that I have questionable plumbing, what's your thought on me replacing both old heaters with ONE 75-gallon heater? Regardless of how the two are currently plumbed, I was thinking of putting in a bigger 75-gal heater and connecting it to the two existing outlets? Do you see any obvious problem/pitfalls with that solution? Thanks for your help!
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Old 07-11-2012, 12:48 AM   #7
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Funky 2 water-heater configuration?


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So given that I have questionable plumbing, what's your thought on me replacing both old heaters with ONE 75-gallon heater? Regardless of how the two are currently plumbed, I was thinking of putting in a bigger 75-gal heater and connecting it to the two existing outlets? Do you see any obvious problem/pitfalls with that solution? Thanks for your help!
That actually sounds logical.....downside....if the water heater goes out...you loose all water....but then again, most of us 'common' folk only have one heater anyway....so that would make you more like us....(i'm trying to inject a little humor here....don't take me serious)

On a personal note.....I would not be able to rest until I knew exactly how that plumbing was ran....I would most likely stay up at night trying to figure it out...
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Old 07-11-2012, 06:49 AM   #8
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Funky 2 water-heater configuration?


Turn everything back on and verify that all faucets are working.

Then repeat your test from the very beginning.

Maybe turning seldom-used valves on and off dislodged sediment that clogged something up, clouding your test results.
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Old 07-11-2012, 08:14 AM   #9
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Funky 2 water-heater configuration?


Make sure that if you have any single lever faucets or tub controls, that that they are not back feeding water into the system and screwing up your test. Shut off the cold supplies to those faucets to prevent that.
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Old 07-11-2012, 10:07 AM   #10
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Funky 2 water-heater configuration?


What is supporting these water heaters? A 50-gallon unit full of water is probably more than 500 pounds. Replace it with a 75-gallon unit and you're talking around 750 pounds. And, unlike your current arrangement, all that weight will be in one place.
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Old 07-11-2012, 10:30 AM   #11
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Funky 2 water-heater configuration?


It is likely that the larger tank originally fed all faucets but could not meet the demand so a smaller one was installed to feed the five but, the supplies from the larger one were never altered. And I agree..watch out for the weight distribution above the ceiling. Also lager tank harder to install. I would replace both but, check the current installations to see if there are any structural concerns. Just drew it out. Now clear. There is a common cold water feed but the tee off to the second tank comes after the shut off valve to the first tank and goes to the isolation valve to the inlet of the second tank hence water shuts off to various fixtures as you described. TADA!!

Last edited by techpappy; 07-11-2012 at 11:03 AM. Reason: further explanation
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Old 07-11-2012, 10:31 AM   #12
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Funky 2 water-heater configuration?


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what's your thought on me replacing both old heaters with ONE 75-gallon heater?
How many people live in the house?

Even if there is a larger number and you actually do need 75 gallons...
I'd rather see 2 basic 40gallon heaters used.
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Old 07-11-2012, 11:09 AM   #13
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Funky 2 water-heater configuration?


How big is the attic? if it's roomy and easily accessed then I would go to one tank as the gas piping and controls can be problematic and expensive to maintain/repair.
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Old 07-11-2012, 12:45 PM   #14
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Funky 2 water-heater configuration?


Or maybe it is really funky. The pipe teeing off to feed both tanks is really the interconnection between the tanks with one pipe going down to feed half the fixtures from there. The single pipe from one tank is the real cold feed. The single pipe from the other tank goes to the other half of the fixtures.
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Old 07-11-2012, 12:53 PM   #15
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Funky 2 water-heater configuration?


That's exactly what I said..only different..as they say in French "maim choes"? (shows) meaning.. same thing Just means you havev to isolate the large tank in order to service any of the fixtures.

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