OWNER

RONCASTLE

2 50 GALLON GAS DOM H/W HTR'S SIDE BY SIDE , HOOK UP IN SERIES OR PARALLEL ? CURRENTLY IN PARALLEL & ONE COOLS DOWN FASTER , 2 DIFFERENT MANUFACTUERS, AM GOING TO CHG. OLDER ONE TO MATCH THE NEWER ONE.

icesailor

Water Heater Piping:

Its my experience that they MUST be piped in parallel and the connections must be EXACTLY equal distance from each water heater. That means that each water heater has the same amount of fittings between the heaters. If one runs out sooner, it is because they are not balanced in the piping.

If you pipe them in series, the second water heater will not come on until the first runs out of hot water.

Slimpickins

why doncha

pipe 'em is reverse return. When I pipe 2 new water heaters that way and set the thermostat the same, both burners will shut down within 20 seconds of each other after a cycle. It's solved a lot of problems after I get a service call for inadequate hot water with 2 tanks piped in series trying to fill a jacuzzi tub. 

icesailor

Parallel/Reverse Return:

Either way will work. DO NOT pipe it in series. If you do three tanks, ALWAYS pipe reverse return.

And Parallel reverse return would probably be just as easy. I just never thought of doing two tanks that way. I usually only see two tanks.

I just find that a lot of installers don't understand the piping requirements so the centered piping seems to be easier to understand.

JMO,

Mark Eatherton

Less fittings...

Chris, piping more than two tanks in a pyramidic parallel versus a reverse return parallel requires more soldered joints. In fact, even with just 2 tanks, it takes 4 more soldered joints going pyramid versus reverse return. Just saying.



Old habits are hard to break.



ME

icesailor

Old Habits:

It's not that much of a habit, it's just something I never thought of for two tanks.

Then, there are the ones who put two water heaters under stairs. A short 30 and a taller 50. I haven't figured out how to pipe one like that. That's a popular way I've seen around.

Mark Eatherton

Parallel reverse return would work for the different size heaters too...

As long as the pressure drop through both heaters on flow is the same, it WILL work. And it looks a lot cleaner than the pyramidic parallel method. A.O.Smith STILL shows the pyramidic parallel method in their installation manual. In most cases, the manifolding ends up in front of the heaters making it virtually impossible to replace just one tank without having to completely shut down all heaters.



When pipe parallel reverse return, with isolation valves placed above the tanks, and unions on the drops going to the heaters, if one fails, you can isolate it and replace it, whole leaving the other tanks on line.



I did a system once that had 6 120 solar storage tanks (solar DHW app). I piped it parallel reverse return DOUBLE COUNTER flow. I;m not sure that the increase in efficiency was worth the extra effort, but it sure looked pretty...



Heres a drawing of a typical pyrmidic parallel piping diagram.



ME

SWEI

Double counter flow?

You got my attention - what is it?



--thanks

RobG

pyrmidic parallel piping diagram

That diagram is very misleading as the inlet and the outlet piping is not equal as must be done with the pyramid system. All pipes must be the same lengthts to create equal flow. I'll go with reverse return any day. JMO

Rob 

Mark Eatherton

4 port tanks...

All top tapped. The cold, on draw would go in one direction, and the hot, on draw out the other direct. Say cold flows from left to right, and hot also flows from left to right, on draw.



The exchange loop would flow in the opposite direction of the draw, right to leftin, and right to left out and the hot as it pertained to vertical profile was also counter flow, hence double counter flow.



I'd have to draw it out for you to see it clearly in your minds eye...



ME

SWEI

a picture would definitely help

I think I'm almost there, but it's not quite clear.



I'm a huge fan of reverse return piping for hydronic distribution and am somewhat shocked it's not more widely used (or understood, for that matter.)  I've had to explain it multiple times - to the same plumbers - on the same job.

Larry Weingarten

So I must ask.

If flow has been taken into account and if temperature is adjusted in the tanks to balance the heating each one must do, what is the problem with series plumbing?



Yours,  Larry

icesailor

Parallel and Series tank piping:

Series piping means that the cold goes in one tank and through the hot to the next tank's cold imlet. Only when the first tank gets cold does the heading device come on. The second tank may not ever come on.

When piped in a parallel reverse return, the pressure is always equal on all tanks. The hottest water will always leave the hottest tank until all tanks reach an equal temperature at the top. If one tank is hotter, it will be the one being used because the hotter water is the lightest and first used.

It is a win-win at all times.

Larry Weingarten

A problem...

...Ive seen fairly often in the field is the imbalance mentioned in the first post, where one tank goes cold long before the other one does.  Dielectrics contribute to the problem by obstructing flow with rust inside the pipe.  A slight flow imbalance, which can happen over time, forces hot water delivery performance to suffer even when it was correctly plumbed in the first place.



I don't see it as an either/or situation, but simply different techniques available to us to use where and when they make best sense. 



Yours,  Larry

jumper

what's wrong with series ?

Set first one to heat to about about 2/3 of temperature rise.

First one runs cool. Second one has less load.