# are these WHs in proper parallel?



## Plumbersteve (Jan 25, 2011)

Had a debate with myself today about this. I had just finished the water lines and turned the water on to start filling when it struck me..."Is this a proper parallel installation?" After a few minutes of internal dialogue and doing finger math in the air, I concluded that it, in fact, is properly in parallel. 

My concern was due to the fact that the two crosses are at different heights. 

What say you? Should a proper parallel installation be piped to the middle? Should the branches come off at the same height? should the total cold and the total hot be equal?


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## MNplumb1 (Feb 17, 2014)

I have never pipes them that way. How is it controlled straight power, off peak? I have always dumped hot into the cold of the second one. That is only on a off peak application though I guess. I have piped commercially that way, but always try to center. I wonder if it makes a difference? Now you have me talking to myself too thanks.


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## rjbphd (Feb 5, 2010)

Plumbersteve said:


> Had a debate with myself today about this. I had just finished the water lines and turned the water on to start filling when it struck me..."Is this a proper parallel installation?" After a few minutes of internal dialogue and doing finger math in the air, I concluded that it, in fact, is properly in parallel.
> 
> My concern was due to the fact that the two crosses are at different heights.
> 
> What say you? Should a proper parallel installation be piped to the middle? Should the branches come off at the same height? should the total cold and the total hot be equal?


You did right.. as long the distance on the inlet and outlet are with 5%.. total...


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## Flyout95 (Apr 13, 2012)

Is that technically parallel? I thought the outlet side had to be equally piped before it took off to the main?


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## Nathan901 (Feb 11, 2012)

Shouldn't the hot main be in the center of the 21" section for a perfect parallel?

I'm sure it will have a very similar draw from both heaters.


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## dhal22 (Jul 30, 2010)

I've always centered both pipes.

David


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## Team BP (Feb 12, 2011)

Ideally you want them centered for equal draw. I've also been told about being within 5% cause nothing out there is a perfect scenario. That's how I've always been told what do too. That's how we install all our water heaters and how our drawings show. I would just take the tees off and center them and reconnect to to your hot and cold and call it done. Unless it's draw that way then leave it but if not I would change it. If you think about it the water will take the path of least resistance to come in and go out that's why they need to be equally spaced. Just do a search there's plenty of info out there on piping multiple water heaters and how it will work.


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## Plumbersteve (Jan 25, 2011)

I forgot to mention that we were changing out dual heaters that were in series. That is why the hot and cold drops were spaced that way. 

Normally, and if I had the space to do so here, we would center the drops. 

I believe that this installation will, in fact, provide equal draw from both heaters. The four inch difference on the hot and cold cancel each other out.


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## plbgbiz (Aug 27, 2010)

With all due respect Steve, why in the world would you pipe it this way? It is neither in series nor parallel. It makes no mechanical sense.

I would say either pipe it parallel or in series, but not whatever this is.


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## Letterrip (Jul 28, 2013)

With all due respect biz, I think you're wrong. The way it is piped, the water has an equal distance to travel in total. If you add the lengths of the cold pipe going in, and the hot pipe coming out, you have an equal travel distance for water passing through either heater. I believe this is an acceptable reverse return parallel.


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## Will (Jun 6, 2010)

I've never piped water heaters this way, but wouldn't you pipe the cold into the first water heater, then hot outlet to the cold inlet on the second water heater, then hot out?


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## Letterrip (Jul 28, 2013)

http://www.plumbingengineer.com/may_12/designers.php


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## Letterrip (Jul 28, 2013)

Will said:


> I've never piped water heaters this way, but wouldn't you pipe the cold into the first water heater, then hot outlet to the cold inlet on the second water heater, then hot out?


That would be series.


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## titaniumplumbr (Jun 11, 2014)

Shouldn't there be a tee in the exact center of each run hot and cold jw


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## plbgbiz (Aug 27, 2010)

Letterrip said:


> http://www.plumbingengineer.com/may_12/designers.php


I don't remember that being covered in my "Appliance Connectors 101" class. :laughing:

I sit corrected and understand the theory behind it. I still probably wouldn't do it personally though.

I am curious where the benefit really is. If you are matching the outlets to be exact reflections of the inlets, would it not be just as simple to split them all evenly on both sides? The link you provided suggests it is better in some pumping situations. I am also curious what those would be and why.

Thanks.


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## MACPLUMB777 (Jun 18, 2008)

Plumbersteve said:


> Had a debate with myself today about this. I had just finished the water lines and turned the water on to start filling when it struck me..."Is this a proper parallel installation?" After a few minutes of internal dialogue and doing finger math in the air, I concluded that it, in fact, is properly in parallel.
> 
> My concern was due to the fact that the two crosses are at different heights.
> 
> What say you? Should a proper parallel installation be piped to the middle? Should the branches come off at the same height? should the total cold and the total hot be equal?


Yes more then height is they have to be balanced between the tee's per all MFG'S specifications, to get equal hot water


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## Best Darn Sewer (Dec 23, 2012)

Letterrip said:


> http://www.plumbingengineer.com/may_12/designers.php


Thank you for the post, Letterip. I too, was unaware of this reverse parallel system. I have always just made sure that the outlets of the two water heaters are all equidistant to the tee where they merge and never gave much thought to the cold side inlets. I have always assumed that if the outlets are equal then they will draw equally.


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## MACPLUMB777 (Jun 18, 2008)

Best Darn Sewer said:


> Thank you for the post, Letterip. I too, was unaware of this reverse parallel system. I have always just made sure that the outlets of the two water heaters are all equidistant to the tee where they merge and never gave much thought to the cold side inlets. I have always assumed that if the outlets are equal then they will draw equally.


Yes that is correct among the reasons for doing this is

#1 you effectively double the output on the tanks gallon wise, as well as double the recover BTU's on the burners,

#2 you get equal wear on both tanks which makes them Both last longer,

#3 I like the way you put double valves on all four pipes this allows one to be totally isolated for service maintenance, or in case of failure of one tank because of burner problems or tank leakage,


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## Best Darn Sewer (Dec 23, 2012)

Plumbersteve said:


> Had a debate with myself today about this. I had just finished the water lines and turned the water on to start filling when it struck me..."Is this a proper parallel installation?" After a few minutes of internal dialogue and doing finger math in the air, I concluded that it, in fact, is properly in parallel.
> 
> My concern was due to the fact that the two crosses are at different heights.
> 
> What say you? Should a proper parallel installation be piped to the middle? Should the branches come off at the same height? should the total cold and the total hot be equal?


I just caught this but are y'all allowed to have valves on the hot side outlets? Here that is not allowed due to the fact that someone not familiar could shut both valves off and potentially create a bomb. I'm not trying to getting some arguments about codes where you are versus where I am but I'm just curious. I do love having them when people put them in for service purposes because it does simplify it but still it is not allowed.


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## Best Darn Sewer (Dec 23, 2012)

JERRYMAC said:


> Yes that is correct among the reasons for doing this is
> 
> 
> 
> #3 I like the way you put double valves on all four pipes this allows one to be totally isolated for service maintenance, or in case of failure of one tank because of burner problems or tank leakage,


That is not allowed here in Texas, Jerry.


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## plbgbiz (Aug 27, 2010)

Best Darn Sewer said:


> That is not allowed here in Texas, Jerry.


Why not?


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## Best Darn Sewer (Dec 23, 2012)

plbgbiz said:


> Why not?


 Because someone unfamiliar with plumbing could potentially turn off the hot side and cold side valves and if that heater is fired up the water has no where to expand to and could create a bomb, potentially. I will say that I do like having a valve on both sides like Jerry said for service purposes but still the code is what it is. It is protecting us from ourselves to an extent.


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## jeffreyplumber (Dec 7, 2009)

Intresting comments on that link. But It doesent confirm the length of pipe needing to be equal etc. I suppose if you set your t stat equal and run hot water see if both heater come on at same time? might give a rough Idea as to if they are feeding equal.


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## Best Darn Sewer (Dec 23, 2012)

The 2012 IPC code does not prohibit a hot side valve at the heater but Texas code does prohibit it. I have seen failed inspections due to it but technically it is allowed according to IPC. I guess its an amendment in Houston or maybe all of Texas. I just know that ever since I've been plumbing here it isn't allowed. I would assume a law suit drove this amendment.


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## Plumbersteve (Jan 25, 2011)

Best Darn Sewer said:


> I just caught this but are y'all allowed to have valves on the hot side outlets? Here that is not allowed due to the fact that someone not familiar could shut both valves off and potentially create a bomb. I'm not trying to getting some arguments about codes where you are versus where I am but I'm just curious. I do love having them when people put them in for service purposes because it does simplify it but still it is not allowed.


Do you have relief valves in Texas?


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## Plumbersteve (Jan 25, 2011)

I'm trying to think of a way to explain this well. Intuitively, I can see that it will have equal draw. 

If you visually isolate the two heaters then you will see that:

Left heater has 8" of Hot and 35" of Cold. 
43" total

Right heater has 14" of Cold and 29" of Hot 
43" total

As long as the totals are the same, the draw will be equal. Of course you need to account for fittings, but in my case, the offsets are both the same. 

This would be much clearer if the tees were centered and the four branches were 10" and the four drops were 10". Then you would see that both heaters have a total of 40" of supply and it would be obvious that they were equal.


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## Best Darn Sewer (Dec 23, 2012)

Plumbersteve said:


> Do you have relief valves in Texas?


I assume you're being sarcastic but of course we do. And I also have plenty of photos where the T&P didn't do its job and a heater ruptured. The reason is because the expansion can happen faster than what a TP can handle. TPs are notorious for failing which is why TXT are a good back up. A good and functional TP can not always deal with the expansion rate on a closed system and that is why many water heaters rupture on closed systems even with a good working TP. I like having valves on inlet and oultets of WHs but here its not allowed. Thats nice that y'all can.


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## rjbphd (Feb 5, 2010)

Best Darn Sewer said:


> I assume you're being sarcastic but of course we do. And I also have plenty of photos where the T&P didn't do its job and a heater ruptured. The reason is because the expansion can happen faster than what a TP can handle. TPs are notorious for failing which is why TXT are a good back up. A good and functional TP can not always deal with the expansion rate on a closed system and that is why many water heaters rupture on closed systems even with a good working TP. I like having valves on inlet and oultets of WHs but here its not allowed. Thats nice that y'all can.


That's why expansion tank are installed... even the code don't required it here.. no die electric unions for me..


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## Plumber (Jan 18, 2009)

Plumbersteve said:


> I'm trying to think of a way to explain this well. Intuitively, I can see that it will have equal draw.
> 
> If you visually isolate the two heaters then you will see that:
> 
> ...


My question is always "who says it's that simple?" and it ain't. MIT and Stanford is always re-testing current beliefs when it comes to hydrodynamics. Google it.

I was taught FI/FO, but never used it. I use the hot to cold and one hot out method. I bet you'd need a physicist to tell the difference between them all, though.


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## MACPLUMB777 (Jun 18, 2008)

THANKS BDS.

I have "not" done any plumbing or water heater installs, in the Lone Star State

I was just going by past experience with the UPC codes in the five states that I 
have done plumbing work and water heater installs in,
but you are right many people do not know that a t&p valve will not release
fast enough for a water hammer or other type of super fast acting pressure
surge,


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## Plumbersteve (Jan 25, 2011)

Best Darn Sewer said:


> I assume you're being sarcastic but of course we do. And I also have plenty of photos where the T&P didn't do its job and a heater ruptured. The reason is because the expansion can happen faster than what a TP can handle. TPs are notorious for failing which is why TXT are a good back up. A good and functional TP can not always deal with the expansion rate on a closed system and that is why many water heaters rupture on closed systems even with a good working TP. I like having valves on inlet and oultets of WHs but here its not allowed. Thats nice that y'all can.


I was being rhetorical and glib. Of course you have T&Ps. It isn't obvious to me though, that they are not sufficient to guard against extreme thermal expansion. 

We are required to install expansion tanks but not put a valve on them which is unhelpful because they constantly leak. 

I wouldn't put a valve on the hot side in a single install. Only in this dual install so one could be isolated if it fails.


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## Best Darn Sewer (Dec 23, 2012)

Plumbersteve said:


> I was being rhetorical and glib. Of course you have T&Ps. It isn't obvious to me though, that they are not sufficient to guard against extreme thermal expansion.
> 
> We are required to install expansion tanks but not put a valve on them which is unhelpful because they constantly leak.
> 
> I wouldn't put a valve on the hot side in a single install. Only in this dual install so one could be isolated if it fails.


I hear ya. I would post photos where they have failed and the water heater ruptured but unfortunately I cannot upload photos to PZ anymore. They will not allow photos with the amount of megapixels that my camera takes now. I could with my old phone but my new one has too high of resolution and there is no way that I had found yet to post them on here from my phone or computer. It may be more prevalent here than where you are at but a lot of houses have double check valves at the meters thus causing them to have a closed system. Often the plumber is unaware or may not know enough about it or how to test for a closed system or to even be cautious of it and consequently does not install a thermal expansion tank.

The last company I worked for had to replace a brand new water heater twice after each one ruptured a week after install before a plumber savvy enough caught what was happening and installed a TXT for the 3rd heater. Both heaters that ruptured had brand new and functioning T&Ps. The water company had installed new meters with internal double checks before the initial install.


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## jeffreyplumber (Dec 7, 2009)

Best Darn Sewer said:


> I hear ya. I would post photos where they have failed and the water heater ruptured but unfortunately I cannot upload photos to PZ anymore. They will not allow photos with the amount of megapixels that my camera takes now. I could with my old phone but my new one has too high of resolution and there is no way that I had found yet to post them on here from my phone or computer. It may be more prevalent here than where you are at but a lot of houses have double check valves at the meters thus causing them to have a closed system. Often the plumber is unaware or may not know enough about it or how to test for a closed system or to even be cautious of it and consequently does not install a thermal expansion tank.
> 
> The last company I worked for had to replace a brand new water heater twice after each one ruptured a week after install before a plumber savvy enough caught what was happening and installed a TXT for the 3rd heater. Both heaters that ruptured had brand new and functioning T&Ps. The water company had installed new meters with internal double checks before the initial install.


Wow So your saying these water heaters were not defective? Or just that they were new? I dont see how a water heater installed would fail that quick with a tand p properly working could do that in a week . Did you ever figure out why they failed or just guessed it must be because it had no txt. btw did the tand p ever burp water out?


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## Best Darn Sewer (Dec 23, 2012)

jeffreyplumber said:


> Wow So your saying these water heaters were not defective? Or just that they were new? I dont see how a water heater installed would fail that quick with a tand p properly working could do that in a week . Did you ever figure out why they failed or just guessed it must be because it had no txt.  btw did the tand p ever burp water out?


Yes, they were new. They were fine from the manufacturer but the expansion of that water caused the tank to rupture. It was a gas heater so the bottom expanded out and made the bottom convex as opposed to it being concave when new. The reason for that is because the heat is at the bottom and the metal is weakened due to that. You can tell it has happened because the nipples at the top will angle towards themselves afterwards.. On an electric heater the top expamds out so the nipples will angle away from themselves whe it ruptures from expansion. 

On this particular job the issue was a double check valve at the meter which made it a closed system. The last plumber who figured it out installed a TXT which fixed it. The T&P did open but it can't fully open fast enough and after a week of high stress on it I guess it couldn't open as much as was needed to keep the tank from rupturing. People and plumbers often don't realize how quickly that water can expand. 

T&Ps open at 210º and 180psi. 212º is the temp for water to boil at sea level which is 14.7 psi. The higher the pressure the higher the temp for water to boil so in a system where the water is under 60psi water will boil at closer to 300º+. The pressure, however, in a closed system will increase very quickly. To test how quick you can put a psi gauge ona boiler drain and see what the static psi is, then shut off the cold side valve of the WH and fire up the heater. Watch how quickly that PSI rises. The T&P can't always open quick enough or allow for enough volume to keep the tank from rupturing. It will work when brand new but if its under constant high stress it won't last long at all. Thats why our new codes require yearly inspections of T&Ps which actually means removing them and visually inspecting them to make sure the thermostatic rod and spring are all good. But once you do that it makes mores sense to just replace it. 

I really wish I could post the photos I have of what I'm talking about but I can't. If you really want them I can email them. PM me if you want them and we can exchange emails.


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## MACPLUMB777 (Jun 18, 2008)

Best Darn Sewer said:


> Yes, they were new. They were fine from the manufacturer but the expansion of that water caused the tank to rupture. It was a gas heater so the bottom expanded out and made the bottom convex as opposed to it being concave when new. The reason for that is because the heat is at the bottom and the metal is weakened due to that. You can tell it has happened because the nipples at the top will angle towards themselves afterwards.. On an electric heater the top expamds out so the nipples will angle away from themselves whe it ruptures from expansion.
> 
> On this particular job the issue was a double check valve at the meter which made it a closed system. The last plumber who figured it out installed a TXT which fixed it. The T&P did open but it can't fully open fast enough and after a week of high stress on it I guess it couldn't open as much as was needed to keep the tank from rupturing. People and plumbers often don't realize how quickly that water can expand.
> 
> ...


I saw the same thing happen at a collage university professor's house,

two rheem 75 gal wtr/htr's

where I was called in a week after the last heater to snake a main line


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## jeffreyplumber (Dec 7, 2009)

Ok Thanks, Dont mean to argue about it. but Im trying to understand why so fast. It must be some kinda perfect storm that caused this.. I guess nobodys home using any water anywhere, mayby fridgid cold at night just askin.. Im just amazed at 2 heaters in 2 weeks, i would have expected perhaps 7 monthes but not 7 days.


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## sparky (Jan 8, 2014)

Best Darn Sewer said:


> Because someone unfamiliar with plumbing could potentially turn off the hot side and cold side valves and if that heater is fired up the water has no where to expand to and could create a bomb, potentially. I will say that I do like having a valve on both sides like Jerry said for service purposes but still the code is what it is. It is protecting us from ourselves to an extent.


supposed to be an expansion tank between the heater and the cold water valve that would take care of the thermal expansion so this should not matter.


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## Best Darn Sewer (Dec 23, 2012)

sparky said:


> supposed to be an expansion tank between the heater and the cold water valve that would take care of the thermal expansion so this should not matter.


That is true and I agree with doing it.


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## Best Darn Sewer (Dec 23, 2012)

jeffreyplumber said:


> Ok Thanks, Dont mean to argue about it. but Im trying to understand why so fast. It must be some kinda perfect storm that caused this.. I guess nobodys home using any water anywhere, mayby fridgid cold at night just askin.. Im just amazed at 2 heaters in 2 weeks, i would have expected perhaps 7 monthes but not 7 days.


It was a small system and summer time and the heater was located in an attic. It would never be frigid here in Houston even in winter. Honestly, I'm not sure why it happened so quick other than it was a small system so expansion happened quickly. Also, it was only a couple there so they probably did not use much hot water which would make the expansion worse and more constant. All in all it was an unusual occurrence but still something that could happen again if the conditions are right.


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## sparky (Jan 8, 2014)

Plumbersteve said:


> Had a debate with myself today about this. I had just finished the water lines and turned the water on to start filling when it struck me..."Is this a proper parallel installation?" After a few minutes of internal dialogue and doing finger math in the air, I concluded that it, in fact, is properly in parallel.
> 
> My concern was due to the fact that the two crosses are at different heights.
> 
> What say you? Should a proper parallel installation be piped to the middle? Should the branches come off at the same height? should the total cold and the total hot be equal?


i think its a dam good lookin job with nothing wrong with it at all other than no expansion tank(s).if the water draw is off a little who the heck cares and what little it would be would make no difference whatsoever.nice job:thumbsup::thumbsup::thumbsup::thumbsup:


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## justme (Jul 4, 2012)

Best Darn Sewer said:


> That is not allowed here in Texas, Jerry.



let me fix this for you , "That is not allowed here in the land of UPC (Houston) Jerry."


I pipe all water heaters with multiple tanks or preheaters with bypass's ,this is accepted everywhere as long as you have a properly sized expansion tank and a T&P valve.


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## MACPLUMB777 (Jun 18, 2008)

sparky said:


> i think its a dam good lookin job with nothing wrong with it at all other than no expansion tank(s).if the water draw is off a little who the heck cares and what little it would be would make no difference whatsoever.nice job:thumbsup::thumbsup::thumbsup::thumbsup:


-

That is what you get when you take a sparky and try to make a plumber out of them !

I know because my contractor partner for 15 years was a sparky but sometimes had a hard time understanding some plumbing problems


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## Best Darn Sewer (Dec 23, 2012)

justme said:


> let me fix this for you , "That is not allowed here in the land of UPC (Houston) Jerry."
> 
> I pipe all water heaters with multiple tanks or preheaters with bypass's ,this is accepted everywhere as long as you have a properly sized expansion tank and a T&P valve.


Ok. I wondered if it was Houston only or all of Texas. .


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## justme (Jul 4, 2012)

This would be a better install with a bull headed tee going to the cold and coming from the hot. The article that was posted is intended for 3 or more heaters and can apply to 2 but the simplest way to pipe in 2 water heaters is bull head setup with equal amount of pipe going to and coming from the heater.


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## Letterrip (Jul 28, 2013)

The reverse return approach is used extensively in solar water heating applications. The Florida Solar Energy Center (part of University of Central Florida) shows it as the easiest method to achieve balanced flow through a bank of collectors without needing additional valving and such. In residential, a bank of panels rarely consists of more than two panels. I'm not saying that it's a superior approach to a traditional parallel. It is however a functional equivent. Given the initial piping setup as per the OP, this may have been the simplest way to run the piping. The first link is to FSEC's site. The second is an article on solar system configurations. Pages 8-10 show collectors piped with reverse return. (In fairness, none show the two panel setup)

www.fsec.ucf.edu

http://www.fsec.ucf.edu/en/publications/html/fsec-in-23-83/in-23-83-4.pdf


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## Plumbersteve (Jan 25, 2011)

The job does have an expansion tank. Just wanted to illustrate the heater supply piping. 

And I'm 100% positive that this installation will provide equal draw on both units. 

I know you guys are sticklers so...I should say, if the heaters were molecularly identical, this installation works. On paper, 100% equal draw.


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## SchmitzPlumbing (May 5, 2014)

what do you guys do on your "perfect parallel" when you have to replace only one water heater and the height of the new heater is different? do you re pipe the whole thing if the new one is too tall? or do you just install it and figure it will work fine.


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## sparky (Jan 8, 2014)

SchmitzPlumbing said:


> what do you guys do on your "perfect parallel" when you have to replace only one water heater and the height of the new heater is different? do you re pipe the whole thing if the new one is too tall? or do you just install it and figure it will work fine.


Excellent question:thumbup:


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## sparky (Jan 8, 2014)

JERRYMAC said:


> -
> 
> That is what you get when you take a sparky and try to make a plumber out of them !
> 
> I know because my contractor partner for 15 years was a sparky but sometimes had a hard time understanding some plumbing problems


So just what are you tryin to say mr jerrymac??that your Trojan machines are junk???lololololo


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