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Old 05-10-2014, 02:07 AM   #1
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2 water heater tanks parallel question


i have 2 water heater tanks set up in parallel.. water heater tank2 broke down a few days, the plumber fixed it by replacing thermopile and control valve.. everything seems fine..

i just noticed today when i opened the hot water faucet.. water heater tank1 burner immediately started, but water heater tank2 is still in pilot light. i waited for many minutes and opened another hot water faucet (kitchen) but water heater tank2 is still in pilot light.. it seems water heater tank2 is acting as a back up..

this confuses me coz the way i'm looking at the diagram below they should act together..





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Old 05-10-2014, 02:10 AM   #2
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2 water heater tanks parallel question


also water heater tank2 is ok coz when i increased the temperature for water heater tank2, the burner worked..

as i said it seems tank2 is acting as a back up..

i wonder if this cause it to break down faster coz it's almost always on pilot light..

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Old 05-10-2014, 02:45 AM   #3
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2 water heater tanks parallel question


based on my research online it seems my parallel water heater is not balanced causing tank1 hot water to be depleted way faster than tank2.

i do notice the outlet pipe for tank1 is not exactly the same for tank2.
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Old 05-10-2014, 07:05 AM   #4
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2 water heater tanks parallel question


Piped up the way the diagram shows, they must be piped equal length.

Or they can be repiped so that the cold water enters through the drain valve port.
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Old 05-10-2014, 11:34 AM   #5
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2 water heater tanks parallel question


what i did is tried to balance the system by partially closing inlet valve for tank1.
i opened hot water faucet, i checked if both tanks burner starts, there's about 2 minute gap.
i'm fine with it. i guess that's the closest thing i can get to getting it balanced.

do you see anything possible problem with partially closing inlet valve for tank1.

i do know re-piping this is the proper way but for now i don't see the need to do that.
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Old 05-10-2014, 12:04 PM   #6
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2 water heater tanks parallel question


Quote:
Originally Posted by dumbengineer View Post

do you see anything possible problem with partially closing inlet valve for tank1.
Yes, there could be a problem if the valve is a ball valve. Ball valves aren't designed for throttling and can become closed.
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Old 05-10-2014, 12:17 PM   #7
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2 water heater tanks parallel question


Thermostats in water heaters are not real accurate. One may fire at at 120 - the other at 110 (example) even though they are both set at the same setting.

While ball valves are designed for quick open or closing, I've seen them used to control flow
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Old 05-10-2014, 01:23 PM   #8
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2 water heater tanks parallel question


this is a pic of inlet valve. is this rated to counter flow of water?


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Old 05-10-2014, 02:54 PM   #9
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2 water heater tanks parallel question


No, that is a Shut of valve.
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Old 05-10-2014, 03:06 PM   #10
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2 water heater tanks parallel question


That's a strange picture- looks like one pipe feeding hot and cold with redundant valves
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Old 05-10-2014, 03:58 PM   #11
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2 water heater tanks parallel question


another pic.. i think plumbing is correct for parallel except it isn't balanced.. and they should have put individual tank pipe outlet shut off valve so i can easily isolate each tank..

now it would seem i cant solve this unbalance water heater without repiping it..


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Old 05-10-2014, 04:04 PM   #12
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2 water heater tanks parallel question


Plumbing parallel systems for balanced control without some type of active regulation is difficult. Even if you have identical lengths and bends, it's never going to be truest balanced. Water is going to follow the path of least resistance.

Too many variables.

I'd put them in series and not worry about it.
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Old 05-10-2014, 05:21 PM   #13
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2 water heater tanks parallel question


Parallel is my preferred method- just like your opening post.
People say if its not piped equally one will draw down faster-work harder. But I have yet to see how much fudge factor is allowable in equal piping. If it was minimal, why don't the manufacturers caution us as to how the flow is affected other then saying equal piping lengths and fittings?
I don't know any parallel water heater install that has flow meters, so it must not be as big an issue as people let on- and I've installed lot's of engineered systems..

IMO- Set your thermostats so they fire at approx. the same time and support that pipe too- it'll snap at the fittings at some point if you don't.
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Old 05-10-2014, 06:10 PM   #14
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2 water heater tanks parallel question


Use the last in first out method. It automatically balances the installation.

The tank the cold enters first is the tank you remove hot water from last. It matters not length of piping our valves used. It will hydro statically balance it self.

Beautiful picture
http://www.bradfordwhite.com/sites/d...S_WITH_TOP.pdf
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Old 05-10-2014, 06:28 PM   #15
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2 water heater tanks parallel question


Quote:
Originally Posted by TheEplumber View Post
Parallel is my preferred method- just like your opening post.
People say if its not piped equally one will draw down faster-work harder. But I have yet to see how much fudge factor is allowable in equal piping. If it was minimal, why don't the manufacturers caution us as to how the flow is affected other then saying equal piping lengths and fittings?
I don't know any parallel water heater install that has flow meters, so it must not be as big an issue as people let on- and I've installed lot's of engineered systems..

IMO- Set your thermostats so they fire at approx. the same time and support that pipe too- it'll snap at the fittings at some point if you don't.
what is the best/easiest way to support those pipe.
can i buy some plastic T post at home depot that i can screw at the base.

i don't have carpentry equipments to do a wood T post.

i saw this at home depot but the price is too much.. anything cheaper?


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Last edited by dumbengineer; 05-10-2014 at 06:33 PM.
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