Right now I have two 50gal (one elec and one natural gas) piped up in Series (on one side of the house). I didn't do this, it was done when we bought the house. We are looking to move a 3rd 40gal natural gas water heater (which is on the other side of the house) out of its location and into the area where the two 50s are. But we'd remove the 50gal electric entirely.

So basically in the end we would have just the 50gal gas and 40gal gas water heater. We could just plumb it in series but id like to do it in parallel. I keep hearing about reverse return parallel but not sure how that works for uneven sized tanks. I hear normal parallel wouldn't would since it wouldn't be balanced and the 50 probably would get used more since it has shorter piping. I read in a few places reverse return works on different sizes but not sure how. I've seen diagrams but they don't show how it works for two and uneven sized tanks.

First off is it possible? If it is how would I pipe it up? Or is it fine to do a standard parallel pipe setup? Its all 3/4" copper piping right now. Or must I buy another 50gal tank?

Also we are fine on the exhaust vent. We have enough capacity on the flue for the additional gas water heater.

Thanks
Dixit

have a good read here...
[www.chinawinds.co.uk]

If the piping and the water heaters are not identical, you may have a problem with parallel. If one is shorter than the other, or even older than the other you may have a problem; been there, done that.

Then again, I have seen it where they are not identical in parallel and they seemed to work fine. Do you wanna risk it though??

Equal pressure drops through both heaters is what determines whether a parallel installation will work or not. But even then, since water is lazy and takes the path of least resistance, a small differential can cause one heater to be depleted while the other still has hot water in it. A series installation is the ONLY way to insure that you get ALL the capacity out of both tnaks.

reverse return (or supply) is the way to go

while not actual water heaters, the principle is the same (equal developed length of the piping through each unit):



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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638



Edited 1 times.

just go series. I used to be a fan of parallel==all things being equal of course, but your not equal, your not even . Even if you were perfectly balanced I think I would still go series, parallel just too much to mess with. Why might I ask are you so set on parallel?

for one, parallel will give you the option of using one heater alone if the other fails.
sure you could pipe a series installation with a by-pass to accomplish the same thing.

You do not even need a bypass, just two "3 way valves" in place of two elbows, and two regular ball valves, instead of the FOUR you need to isolate a parallel pair.

whatever how many valves, to isolate one tank from other ... I just cant remember the positives of parallel over series.... and often think a 50usg tank is just as adequate as 2 40usg.. unless filling a big tub..refresh my memory please

Two valves on each tank to isolate them, and the hourly recovery rate is MORE important than the initial tank volume. Two heaters, of any size, will have twice the recovery of a single one, plus with two 40 gallon ones you start off with 50% more hot water before the recovery starts. This assumes BOTH heaters are contributing equally, which is NOT a given if they are in parallel.

Sorry been away for a few days. Im not dead set on series, but Ive always done my houses in parallel. Series just seems like one tank going to get used way more than the other since the 2nd one in line will act as a storage tank more or less since its already getting heated water from tank1.

This is for about a 9200sqft house, we have about 6 full baths. We only have 4 people in the house now, but as the kids get in their teens that probably means longer showers.

If we did the parallel then we would put in 4 valves so we can isolate either one. In series you can only isolate the 2nd one technically (in the setup I have now with the 50gal gas as the first tank and 50gal electric as the 2nd one).

Parallel reverse just seems like I have to get the pipe length about the same. But how does the tank size come into play? Obviously the 40gal is shorter so its travel is less.

Yes getting hot water out of both tanks is basically the key if it comes down to that (like is one kid takes a long shower). But also want good recovery. Not sure how well series plays into it. Just seems the 2nd tank is going to get barely maybe 10-20% use compared to the first tank which will be working overtime essentially as most of its water ends up in tank2.

Sorry I just haven't fully seen or used the benefit of series yet. Ive had hotels where we've had multiple tanks (different sized) where they were all setup in standard parallel, not series. Never really noticed an issue for that.

Dixit

And what is wrong with tank #2, "idling" except when you use a lot of water? All that means is the the first tank will probably fail a long time before the second one does, so you only have to replace one tank, and you know that you will ALWAYS get the maximum amount of hot water from the tanks. With parallel, you are depending on "fluid dynamics" to do it and they do NOT always work the way you want them to.

'(parallel) reverse return' will AUTOMATICALLY ensure the same developed length through each unit - period - don't overcomplicate a very very simple piping arrangement

this is how different sizes of convectors are hooked up to insure VALVELESS flow balancing

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638