# Hot Water Tanks - Parallel versus Series



## Scott K (Oct 12, 2008)

I'm curious if you guys have an opinion on which is better for durability, longetivity, service, etc, - piping 2 hot water tanks in series, or in parallel?

I would think that in general for serviceability, parallel is better because you can isolate the tanks if one goes, provided you insall shut off valves for said purpose.


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## 422 plumber (Jul 31, 2008)

I pipe them in series, with bypass valves so they can be isolated, if needed.


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## user4 (Jun 12, 2008)

I always pipe them in paralell, when they are piped in series one tank is doing all the work for the other tank, unless you are talking about a series of tanks in a heavy commercial application, like a hotel laundry.


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## Scott K (Oct 12, 2008)

Well I think about the benefits and pitfalls of the 2 different installation all the time (at least when it's on my plate to do at some point on the job) and I always wonder if there is something I'm missing in the scheme of things when I debate the merits of one versus the other, hence why I'm asking your guys opinions.


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## SPH (Nov 4, 2008)

Scott, I had the same question just recently, i have 4 commercial tanks that i have to install and im considering reverse return for the installation. I think it would make it easier for the install because you dont have to worry about EXACT equal distances between the tanks to even things out. 

I dont think series is the best idea because the first tank would be doing most of the work.


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## Scott K (Oct 12, 2008)

Well parallel doesn't bug me so much. I mean getting the distances right isn't too big of a deal. The only thing that irks me about parallel is the whole issue of what about that one variable that causes one tank to work harder than the other that you might not be able to do anything about i.e. more water somehow flows through one for whatever reason, perhaps the pipe were reamed differently, or there was a piece of debris in one of the tanks you didn't know about, or something was manufacturered differently, etc. Serviceability parallel is easy to service if you have isolation valves or one tank goes, etc. 

But then I always wonder about something along the lines of what about running them in series and having them slightly oversized, and then have one tank set at 110-120 and then the most downstream tank set at 140. So the first tank doesn't work AS hard, and then the next tank bumps it up. Might have more equal heat load, wear and tear, etc.


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## eddiecalder (Jul 15, 2008)

SPH said:


> Scott, I had the same question just recently, i have 4 commercial tanks that i have to install and im considering reverse return for the installation. I think it would make it easier for the install because you dont have to worry about EXACT equal distances between the tanks to even things out.
> 
> I dont think series is the best idea because the first tank would be doing most of the work.


You don't have to worry about exact measurements because i'm installing it. :laughing:


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## SPH (Nov 4, 2008)

eddiecalder said:


> You don't have to worry about exact measurements because i'm installing it. :laughing:


whatever, you will probably just get Richard to do it.

Scott, Interesting idea about setting the temperature points, that might work. You would have to find the incoming water temperature and divide it by the number of tanks to find your set points so it was even.

I know what your saying about the pain of the unknown variables for running in parrallel and it seems that every install. Or even later down the road when one tank goes and a new tank is brought in that doesnt quite match up.

This is making really think that reverse return is the best idea.


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## 422 plumber (Jul 31, 2008)

www.castlemanplumbing.com/images/p1010087.jpg


check this lollapalooza out. I am not posting it because it may be copywritten.


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## Jaret (Mar 4, 2009)

Depends on the application. We did a huge restaurant in a casino in Vancouver. They we done parallel.


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## Pdesign (Mar 5, 2009)

Question?
Does the manufacturers installation have anything to do with that?
When I have a building that requires 2 water heaters I must show them on drawings with the same length pipes so one is not working harder than the other.


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