Dual water heaters, can I shut one off while waiting for repairs

[Ryan Sims]

Hi I've gotten a lot of useful info from this site for a while - right now I haven't found a thread where someone asked this particular question - not sure if it's a stupid question or not. Basically I've got two water heaters, one has developed a slow leak, looks like it's coming from the anode rod and possibly cold water in. They are both 12 years old, and we have hard water here, so I figure I'll replace them both to be safe but can't do it for a week or so. I'd like to turn the leaking one off to avoid any horrible problems (these are in the attic). The thing is, I can't tell if they are in parallel or series - they are in an attic and about 50 ft apart, so I can't see how the piping runs due to insulation etc. They are both set to hot, and after running the hot water in a tub for about a minute, the intake pipe for both heaters seemed to still be cool, so I'm assuming they are in parallel? It's very hot here so a little hard to tell if the pipe had warmed up or not, just tried a quick test.

Main question - since I can't tell if they are in series or parallel, if I shut one of them off and close its in valve, will it cause any major problems or safety issues if they happen to be in one configuration vs the other? I guess I'm wondering what would happen if they were in series and I closed the valve for one of them. I plan to leave it off and disconnected for a week or two while I find replacements etc. Thanks!

 

[Reach4]

Being so far apart, that makes it more likely they are supplying different areas of the house.

Series is more common than parallel. But parallel is certainly possible, especially after your cold intake pipes.

Electric? Turn off one breaker, and see what happens.

 

[Sponsor]

 

[Ryan Sims]

Being so far apart, that makes it more likely they are supplying different areas of the house.

Series is more common than parallel. But parallel is certainly possible, especially after your cold intake pipes.

Electric? Turn off one breaker, and see what happens.

So yes they are both gas, and I believe they are connected because a few years ago, the hot water would quickly switch from hot to cold during a shower, and we found that one of the heaters had gone out. Once that heater was turned back on, hot water was back to normal. I'd imagine this would also indicate parallel. I'm just a DIY guy so want to make sure I'm not potentially creating a bad situation by turning one of the heaters off and closing the valve without being sure of the configuration.

 

[Reach4]

If you close one valve, and if you still get hot water, they were not in series.

I see no danger in closing one intake valve on a heater that is turned off. To be able to remove that WH, you would need a valve on the output to isolated things also. I think you have figured this stuff out already.

 

[Ryan Sims]

Thanks for the replies - since you mention it, I did notice that neither heater has a valve on the output side - thoughts?

 

[Reach4]

Put one in vacation mode, or off if auto-light pilot, and close the valve. Observe the effect.

 

[Ryan Sims]

OK I'll check it out - thanks again

 

[BrianFtx]

Hi all,

DIY guy here. Reviving this thread as I have a similar situation. Two Gas water heaters installed right next to each other at same height (one in a closet, the other just outside the closet).

One was replaced this past summer (New), the other is 15yo old (Old) started leaking last night, then the entire drain valve completely broke off the tank. Like the OP, I'm not sure how they are plumbed, and not sure what is safe to do here. The New heater has a shut off on only one line (I'm assuming in inlet line). The Old heater has shut off valves on both lines.

Currently I have turned off the gas to both heaters, and both lines on the Old heater are shut off. The Old tank is empty. With this set up, I still get water coming from hot water tap, it's just no longer hot.

My question is this: can I restore gas/heat to the New heater and have hot water supply for the house while the Old heater is completely shut off & turned off?

My thought is that, if they were plumbed in series, then shutting both valves on the Old heater as I have done would stop water from coming out of tap when hot side tap turned on. Unless the New tank is the second tank in the series and it is somehow drawing water from the new tank outlet despite the fact that there is no new supply coming into it. Seems like shutting both valves on either tank would stop hot water from making it to a tap's hot side.

This leads me to believe they are parallel, which hopefully means I can relight pilot and restore gas/heat to the new heater while the old heater is completely shut off, allowing me to have hot water until the Old tank is replaced.

Does this make sense?

Thanks for any thoughts/advice!!

 

[Reach4]

BrianFtx, if in series, yes no problem. If in parallel, if they had separate inlet valves, which seems likely to me, then yes also. I am not a pro.

 

[BrianFtx]

If series, wouldn't shutting down Old heater stop the hot water supply altogether, regardless of where they each are in the series?

 

[Reach4]

If series, wouldn't shutting down Old heater stop the hot water supply altogether, regardless of where they each are in the series?

If you closed down the power/gas to the first of two, that would not be a problem. The first would just pass the water to the second.

If its the second one shut down, that is a problem, because it would give the worst case of slow hot water ever. When I responded the first time, I failed to consider that. In that case, I would hope the plumber provided a bypass valve system around the second WH.

 

[BrianFtx]

Reach4,
Thanks for your help.
Back to my other question though: with the old heater completely shut off (no gas, both inlet and outlet valves are closed, and it's got an open hole at the drain plug!) and water still coming out of hot water tap in bathroom (it's cool water though as gas turned off to New heater as well), is this proof that these are plumbed in parallel?

 

[Reach4]

Reach4,
Back to my other question though: with the old heater completely shut off (no gas, both inlet and outlet valves are closed, and it's got an open hole at the drain plug!) and water still coming out of hot water tap in bathroom (it's cool water though as gas turned off to New heater as well), is this proof that these are plumbed in parallel?

Yes. I had missed that part.

 

[hj]

The third option is that the heaters are NOT interconnected, but independent given that they are remote from one another. If so, then shutting off one has absolutely NO EFFECT on the other. There is almost no way you could ever balance a parallel system with the heaters separated like that, and the piping would be a nightmare.