Review my water heater design

[Atl_Rob]

Hi all,

I'm about to replace a couple of old failing water heaters and I wanted to double-check that my design is sound. The current system works but I believe it's not plumbed correctly. Each water heater feeds a separate floor and each has recirculation return line. The return lines are merged and fed by a single recirc. pump. There are no check valves on the cold lines, so we frequently get warm water from cold side of sinks. There is only one expansion tank and it is flooded.

Here's the new design. I realize that ideally I would add another recirc. pump, but I'd like to keep using the current single setup for now to save some $$. I'm adding two new expansion tanks and moving the ball valves before the expansion tanks (instead of after). Also adding check valves and plumbing the return to the cold line instead of drain. Please let me know if this will work.

 

[Reach4]

Seems complicated. However, do you need a way to let flows K and L be roughly equal? Maybe it works out that way that the resistances are similar.

Are you going to run your pump 24 hours per day?

The old connections at the bottom allowed a gravity assist, but your change makes for easier connections.

 

[Sponsor]

 

[MACPLUMB]

Yes looks great to me,
The separate expansion tanks and after ball valves is what I was going to point out was wrong in the first drawing

 

[Atl_Rob]

Seems complicated. However, do you need a way to let flows K and L be roughly equal? Maybe it works out that way that the resistances are similar.

Thanks for your reply!

That's a good question. Somehow it is currently working, that is, all upstairs and downstairs bathrooms get near instant hot water. I probably have an efficiency problem (water circulating faster through one of the water heaters). If you can think of an easy fix, please share. If not, I may just leave it for now and upgrade to dual pumps in the future.

Are you going to run your pump 24 hours per day?

That's how it's been running. This is a fairly new house to us, so I'm still trying to figure things out. I realize that running 24/7 may not be the best for the gas bill. I was thinking of attaching the existing pump to an external timer.

 

[Reach4]

Timer would be good.

You could feel the return lines. If one is much hotter, you could add a valve into that line to slow its flow.

 

[MACPLUMB]

Go to GrundFos pumps I think they have a timer/controller that you can set to turn on from upstairs or even remote

 

[Master Plumber Mark]

I think that you would be better off if you installed 2 small timered pumps and separated the lines for k and L into the
heaters.... and then took them down to the bottom of the heater instead of tieing them into the heaters on the top

you could eliminate all
the extra check valves and there would be no way the units could back flow up the cold lines or leech across
you would only need check valves on the incoming cold lines....

 

[hj]

He would STILL need the check valve in the lines after the pumps and he should have "control valves" either before or after the return check valves so he can control the flows and equalize them, (also slow down the flow to minimize high velocity erosion). This would eliminate ball valve "G".