# 2 water heaters. tandem or series?



## rob the plumber

How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol. 
Pros, cons?


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## ChrisConnor

rob the plumber said:


> How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol.
> Pros, cons?



I prefer parallel ( which I think is what you called tandem). Just gotta keep your piping lengths right.


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## Titan Plumbing

Depends on the needs.


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## greenscoutII

Parallel... Always parallel..


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## markb

Reverse return or parallel. Depends on which is easier.

Sent from my iPod touch using PlumbingZone


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## easttexasplumb

Just install one tankless, it will work.


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## beachplumber

When running im parallel if your piping isn,t the same length will one heater not work more than the other. I realize in series the first tank is gonna run more.

I usually run in series (electri)


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## TPWinc

I would think that there would be a little more to balancing the draw on parallel installs than just pipe length. Difference in flow restriction in the heat traps and dip tube will affect the balance won't it. There could also be and issue with sediment build up, which will be higher on a parallel install, due to spliting the flow rate in half. Of course it does depend on the application and why you are useing two heaters and not one. You are not SOL when it comes to removing 1 heater out of a series system if they are plumbed correctly. I install all series heaters with a bypass.


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## rob the plumber

The bigger houses I've done are usually 2 50 gallon power vent heaters. I think the piping looks flossier in tandem, and if one heater fails, you can shut the ball valves and remove the bad heater while leaving hot water available. I think one heater does all the work when plumbed in series.


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## TPWinc

rob the plumber said:


> The bigger houses I've done are usually 2 50 gallon power vent heaters. I think the piping looks flossier in tandem, and if one heater fails, you can shut the ball valves and remove the bad heater while leaving hot water available. I think one heater does all the work when plumbed in series.


One heater doesn't do all the work, but it does do alot more than the other. Because of this the second heater recovers quicker. You can remove one out of a series and leave hot water available if plumbed correctly. The tandem or parallel is a cleaner and easier install though.


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## mccmech

rob the plumber said:


> How do you guys plumb 2 heaters? I always run them tandem. I think its best for both heaters to be fed and worked evenly. When run in series, one heater is basically just a storage tank. You also can shut down and remove one heater when run tandem. In series you are sol.
> Pros, cons?


I don't agree that you're s.o.l. if run in series. You can put in the isolation valves & tee to allow by-pass of either unit in the event of maintenance/replacement of either unit.


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## Michaelcookplum

Left set to low, right set to high (normal setting). 9600 sq ft home 9 bath. To answer you question though, I think it all depends on size of the heaters, efficiency or recovery rate, gas vs electric, needs of homeowner/builder. So there are a few factors to through in the mix.


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## plumber666

My experience with this has often started in an apartment mechanical room with the manager saying, " I've run this building for 20 years and we've never had an issue with this hot water heater. The one beside it, however, has been changed 5 times."

Without fail, the original installation was series tanks. The one with the cold water inlet does all the hard work, the other one just simmers quietly to itself.

In my umpteen new school builds and oodles of reno's, I've never seen series tanks on a blueprint.


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## 1703

We all know that undersizing a water heater is bad news. Customer is not happy because they're running out of hot water and when talking gas heaters, the flue condenses. So when the demand is such that two water heaters are needed to eliminate the unhappy customer and a series arrangement is used, the first one experiences the same set of issues an undersized water heater does, IMO.


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## 100 Watt

Michaelcookplum said:


> Left set to low, right set to high (normal setting). 9600 sq ft home 9 bath. To answer you question though, I think it all depends on size of the heaters, efficiency or recovery rate, gas vs electric, needs of homeowner/builder. So there are a few factors to through in the mix.


 
Wow, 2 flue vent heaters in a new build!! Been a few years since I've seen that. And what is that orange colored piping feeding them? Must be a new plastic...

We typically install in a series. I'm sure that the primary tank will die first. But not sure it would die any sooner than installing just one heater. I'm thinking we're gaining a few more gallons this way. (I'm no engineer, just a plumber) Seems like most of the time we end up with a 50 gallon power vent as primary and 50 gallon electric as the storage tank. 

Not a fan of tankless for big houses. People always bi**h about hot water pressure. Most of the people who can a afford a monster house don't care about saving a few $$ on energy. A $300+ gas bill doesn't bother them.


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## frisco kid

I plumb them in parallel.


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## 422 plumber

I have seen parallel installations where one does all the work, and the other is just on standby. I usually pipe in series, because most of my dual installs are really just adding a heater to an existing one, and there isn't room or time to pipe in parallel, so I go series. The first heater is usually set at 135 and the second at 145, by the time the water gets to dish machines, it's 140.


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## ILPlumber

Parallel. First in --- last out

Nobody cares that this was sent from my droid using. Plumbing Zone


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## SewerRatz

ILPlumber said:


> Parallel. First in --- last out
> 
> Nobody cares that this was sent from my droid using. Plumbing Zone


Here is a diagram of the First in --- Last out parallel piping, its quick its easy and it works all the time.


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## plbgbiz

Ron,

Don't the tees have to be equally spaced between the WH's to draw equally?


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## SewerRatz

plbgbiz said:


> Ron,
> 
> Don't the tees have to be equally spaced between the WH's to draw equally?


When you do the first in last out method, the tees pretty much automatically space them selves out equally. The idea is the first tee on the cold supply is by the first heater so it gets the cold water first, and the second heater has the other tee on the hot side, the distance between the tee's and the other heater will be the same, and the second heater is the first one out which makes the one getting the water in first to be last out.

Do not ask me the physics behind it, I am not that good at explaining it. All I can tell you is it works.

Here is another diagram from ao smith with three heaters, and you can do this all day with as many as you want.


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## plbgbiz

Great info. Thanks. :thumbsup:


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## gitnerdun

So what happens when the hot outlet clogs with scale, rust, or some crap? The other heater will then take all the demand and won't be able to keep up. Customer complains of running out of hot water, but the elements and Tstats check out good. This is the reason I do it in series. Parallel seems like there is room for trouble maintaining steady temp.


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## ILPlumber

gitnerdun said:


> Parallel seems like there is room for trouble maintaining steady temp.


Not really. I use a manufacturer recommended and code required temperature mixing valve on the combined outlet.........

It is the only way multiple tanks get piped from my shop. My way is always the right way. Just ask me..


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## gitnerdun

mixing valve does make sense:thumbsup:


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## antiCon

always tandem installation is best... (in series).. my mentor always called it piggy-backed


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## SewerRatz

If plumbed in series, wouldn't it make sense to set the first heater to 90 degrees, and the second heater to the 120 degrees? This way both heaters will only have to do a 40 degree temp rise each and both get equal use then. Our average inlet water temp here is 50 degrees so my math works for us.

I still agree 100% with ILPlumber first in last out is the best and only way to plumb in more than one water heater.


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## Gettinit

SewerRatz said:


> When you do the first in last out method, the tees pretty much automatically space them selves out equally. The idea is the first tee on the cold supply is by the first heater so it gets the cold water first, and the second heater has the other tee on the hot side, the distance between the tee's and the other heater will be the same, and the second heater is the first one out which makes the one getting the water in first to be last out.
> 
> Do not ask me the physics behind it, I am not that good at explaining it. All I can tell you is it works.
> 
> Here is another diagram from ao smith with three heaters, and you can do this all day with as many as you want.


This his called reverse return. 

It is the easiest and fastest way to equalize the piping. If you put it in. Series you will not be utilizing both heaters 100% like RR or the older equalization method.


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## Gettinit

Just remember one thing about RR. You put the cold main into the first water heater and you pull the hot out of the other water heater at the end.


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## Master Mark

*series is the best method*

:thumbup:SERIES IS THE BEST :thumbup:
 
Parallell never draws equally in the first place... most units installed in parallell never draw equally anyway from day one......one heater always does more of the work than the other one...... Unless you install gate valves and flow meters on the units to guage them properly...... which is a joke in the real world... 
 
dont forget that over time those dialectric unions
start to corrode on top of those Parallell heaters and eventually the two units are totally out of sync.....

 dont forget that lets say 5 years from now one of those parallell heaters starts to leak,,, 
 the new unit you install ,, under warranty, probably wont be a perfect exact match, so they wont draw equally once you butcher up the plumbing to get the new unit installed in PARALLELL.... 

*We run into this issue all the time....:blink::blink:*


if you install them in SERIES you never have an issue with even or restricted flow.... 

 and you certainly get a full 80 or 100 gallons of hot water versus only maybe 60 gallons off a parallell restricted clogged up unit..


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## SewerRatz

Master Mark said:


> :thumbup:SERIES IS THE BEST :thumbup:
> 
> Parallell never draws equally in the first place... most units installed in parallell never draw equally anyway from day one.........
> 
> ....dont forget that over time those dialectric unions
> start to corrode on top of those Parallell heaters and eventually the two units are totally out of sync.....
> 
> dont forget that lets say 5 years from now one of those parallell heaters starts to leak,,,
> the new unit you install ,, under warranty, probably wont be a perfect exact match, so they wont draw equally once you butcher up the plumbing to get the new unit installed in PARALLELL....
> 
> *We run into this issue all the time....:blink::blink:*
> 
> 
> ~snip~


If you plumb it in first in last out like the pictures I posted, they will always draw equally. As for dielectric unions, I use brass unions which is allowed per our code. Watts also makes a brass dielectric union.


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## Master Mark

SewerRatz said:


> If you plumb it in first in last out like the pictures I posted, they will always draw equally. As for dielectric unions, I use brass unions which is allowed per our code. Watts also makes a brass dielectric union.


 
it appears that your sketches are for more of a commercial application....brass dialectric unions probably cost 5 times more than the average residential parts we deal with every day....

no one ever goes through that kind of trouble and expence here in the boondocks of Indianapolis..... 

I am thinking about the common home plumbing systems we run into every day....which are usually not installed with anything but the cheapest stuff you can install....

still like in your skecth,
that when one of those goes bad, and has to be replaced with something not exactly similar....
it pretty much messes up the mojo and flow for all 
three of them...


so what have you been up to this year so far??.


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## Donahue756

always parallel. that's how i was taught. And that's how Bradford white wants them


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## SewerRatz

Master Mark said:


> ~~~~~~~~~~~~~~~
> 
> ~~~~~~~~~~~~
> 
> 
> 
> so what have you been up to this year so far??.


Trying to stay alive, health wise and work wise. I am going to start going to commercial places and hotels, and introduce myself and give them some info about our company.


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## Gettinit

Donahue756 said:


> always parallel. that's how i was taught. And that's how Bradford white wants them


That is reverse return....same thing as seweratz pic.


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## Gettinit

I will also add the tanks need to be the same. This is to ensure proper draw due to different pressure drops.


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## Gettinit

Master Mark said:


> it appears that your sketches are for more of a commercial application....brass dialectric unions probably cost 5 times more than the average residential parts we deal with every day....
> 
> no one ever goes through that kind of trouble and expence here in the boondocks of Indianapolis.....
> 
> I am thinking about the common home plumbing systems we run into every day....which are usually not installed with anything but the cheapest stuff you can install....
> 
> still like in your skecth,
> that when one of those goes bad, and has to be replaced with something not exactly similar....
> it pretty much messes up the mojo and flow for all
> three of them...
> 
> 
> so what have you been up to this year so far??.


You have to use dielectric unions here for water heater. If you have more than one tank type heater. It really is a piece of cake. If there is room it is more cost effective and better to have two 40's than one 75 gallon electric heater.


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## OldSchool

Tipsforplumber said:


> So many, in fact, that we've created a special program for our most enthusiastic customers called our Advantage Plan™. Ask your Mr. Rooter Plumbing professional about this exciting program and how it can help you cut the cost of your home plumbing services. Our plumbers enjoy their work and it shows! We look forward to welcoming you as a customer and being your preferred plumber in the future. There's a reason they call us Mr.®
> 
> plumber brea


I wonder who you work for

Sent from my miniature laptop


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## SewerRatz

OldSchool said:


> I wonder who you work for
> 
> Sent from my miniature laptop


Old School, if you quote a link spammer, you should remove the spammed links.


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## Redwood

Tipsforplumber said:


> So many, in fact, that we've created a special program for our most enthusiastic customers called our Advantage Plan™. Ask your _Mr. Shiot for Brains _Plumbing professional about this exciting program and how it can help you cut the cost of your home plumbing services. Our plumbers enjoy their work and it shows! We look forward to welcoming you as a customer and being your preferred plumber in the future. There's a reason they call us Mr. Shiot For Brains®
> 
> Spammer


Hey Thanks for stopping by don't let the door hit you in the azz... :furious::furious:


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## Redwood

SewerRatz said:


> Old School, if you quote a link spammer, you should remove the spammed links.


Or mess em up like I did... :laughing:


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## U666A

tipsforplumber said:


> so many, in fact, that we've created a special program for our most enthusiastic customers called our advantage plan™. Ask your mr. Rooter plumbing professional about this exciting program and how it can help you cut the cost of your home plumbing services. Our plumbers enjoy their work and it shows! We look forward to welcoming you as a customer and being your preferred plumber in the future. There's a reason they call us mr.®


gtfooh


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## easttexasplumb

Tipsforplumber said:


> So many, in fact, that we've created a special program for our most enthusiastic customers called our Advantage Plan™. Ask your _Mr. Rooter _Plumbing professional about this exciting program and how it can help you cut the cost of your home plumbing services. Our plumbers enjoy their work and it shows! We look forward to welcoming you as a customer and being your preferred plumber in the future. There's a reason they call us Mr.Hack.


 
:arabia:


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## OldSchool

SewerRatz said:


> Old School, if you quote a link spammer, you should remove the spammed links.


If I did that I would be taking work away from biz and the other mods....

Sent from my miniature laptop


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## paulheck

despite of anything i always prefer series


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## Logtec

paulheck said:


> despite of anything i always prefer series












despite what you say, a Reverend prefers you to be banned.


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## sparky

I pipe them so neither one lasts very long so I can go back and replace them in five yrs


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