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My vote is no..
Do it in series and insulate all piping well.
The different lenghts of piping, both hot and cold will give one heater an advantage if you will, via less friction loss thus it will work more and when it runs out of hot water it will deliver cold water and your other water heater could sit there and stay hot and not be drawn from.


(Plagerized below)
Another important point of parallel installation is the length of the supply piping and delivery piping – they must all be the same length. As shown in the drawing below, section A-E must be the same length as section A-B; C-D must be the same length as F-G; E-F must be the same length as C-B. The same holds true for the hot water outlet side. Because the water pressure is constant along the cold inlet piping and hot water supply piping, the heater with the closest 'run' will do the majority of the work. To prevent this we ‘balance’ the unit with equal pipe lengths. When installing heaters (and storage tanks) in parallel, it is important to accurately plan and measure the distances from the cold water supply pipe to the heaters and from the hot water outlet on the heater to the hot water supply line. This will equalize the work between the two water heaters.
 

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I would never pipe heaters in series unless I was doing more than two, and if that was the case I would consider a boiler and storage take above multiple heaters.
 

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Discussion Starter #9
A friend piped the water this way in a new house, I believe he already split the system back up. When he first piped it that way it was on accedent and he asked me if it was okayto leave it. I told him it was okay piping the heaters in parrellel but I didn't know about having them on opposite ends of the house.
 

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SewerRats
I don't particularily agree with BW's piping schematic. What is it about the design that you like? I have to wonder about the draw on a last out method.
tl
 

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SewerRats
I don't particularily agree with BW's piping schematic. What is it about the design that you like? I have to wonder about the draw on a last out method.
tl
Well first you can install an odd number of heaters easily. Plus it is easer to keep this type of manifold evenly sized on both sides. I see the first in last out install mostly in commercial installs and see all heaters working evenly. Where as the standard parallel install I see in residential homes, I have seen more failed water heaters due to, where one pipe leading into the tee is a hair longer than the pipe from the other heater, which causes the heater with the shorter piping to work harder.

The first in last out method is also taught by the Local Union shops out here.
 

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SewerRatz
I'm just not quite convinced. Your points are good but I'd really be interested in BW engineered studys to have them promote this type of installation. These guys are in the business of selling product. It would suprise me if they gave us a model whereby it promoted a longer tank life. From their drawing, the pressure release point is after the second tank. The draw, in my opinion, is heavier on that tank. A good old flow meter would either prove their design either right or wrong.
Don't get me wrong. I'm not being critical of their opinion. I only hope that this kind of dialogue makes all the more informed at the end of the day. This is a great form for all of us to exchange ideas and be masters of our trades.
cheers
tl
 

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Protec
Do you think the tanks draw evenly? If you do, what is it based on?
Here's where I'm comming from.
Anytime piping is uneven or there are restrictions of any kind, you will encounter hydraulic resistance. That resistance will have a direct effect on flow and in closed piping systems, head.
The system BW put out for us to follow is fine. It will work. But nobody should be under the illusion that it is the end all be all of a multi tank system.
The 2 problems I have are with the longer, and uneven pipe length from the second tank. Even though the difference is minor, there is a difference. That difference will have an effect on flow, albeit small. But I wouoldn't want to be on record saying the first tank works harder because of the unbalanced piping. Why? I think a much bigger problem in a system piped like this is the fact that the first tank comes out of a 90 and the second out of a "T". What do you want to bet that the first tank bully's it's way past the second. If the "T" was directional, different story. But how many designed systems have you run into with directional "T's". Not many I bet. It`s like the old argument about air flow in a ducted system going into a straight or directional defuser. Where do you get the best flow in this case. I think the BW system will definately work in a pinch.
I like an equal draw system that is balanced. But that`s only my personal preference. The science of hyraulics is a bit fun isn`t it though.
tl
 

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So Bw has èxactly the same lengths of pipe in the system. Since the pipe lenghts are identical you say the draw is equal. Are you saying the system draw evenly because BW says it is
 
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