The Tank › Multiple Tanks
- December 13, 2013 at 7:43 am #20397
We replaced two 40 gallon Bradford White “low boys” recently and changed the configuration based on the plumber’s recommendation.
Originally, they were installed such that hwh #1 fed hwh#2 which provided the hot water. Normally it is just my wife and I so this seemed to be a waste of electricity maintaining 125 degrees in two tanks as we never needed more hot water than what a single 40 gallon tank would provide.
We do need both tanks when our children visit 2 – 3 times per year.
When we replaced the tanks a few months ago the plumber installed shut off valves such that we can have tank 1 separate from tank 2 and use either or both. I plan to rotate between tanks every 3 months.
My question is, when we do want hot water from both, will the water pressure coming out of the two tanks be different if both valves are fully open and will the tank closet to the output be the only tank providing hot water? We have the kids/grandkids visiting at Christmas so I don’t want to find out then that this new configuration won’t work as planed!
AlDecember 13, 2013 at 2:46 pm #20398
Hello: The two usual configurations are called parallel and series plumbing. Originally your system was series plumbing. I’m not sure from the description what it is now or how to control it. Series is more efficient if you don’t need high flows. Parallel can be tough to balance and keep balanced over time. With series plumbing and low usage, just turn off power to the first (upstream) tank. When the kids come to visit, turn on power to the upstream tank as well.
I think a photo of what you have now would help for us trying to give advice on what valve to turn. 😎
Yours, LarryDecember 17, 2013 at 4:24 pm #20404
Hello Larry. Attached is a picture of the two tank setup, I hope it shows what you were looking for. The plumber configured it such that I can completely shut off either tank and it is my plan to rotate between tanks every 90 days.
Is this set up what you would consider “parallel”?
It is currently set up with the tank 1 cold input valve and hot output valve shut off and I am using tank 2.
When the kids visit I will turn tank 1 back but my concern is whether or not tank 2 will be contributing to the overall hot water output given tank 1 is closer to the hot water output (hot water runs right to left in the picture).
Is this what you were referring to when you talked about the “balancing” issue?
How can I determine if they are balanced or what steps do I take to balance the two tanks?
AlDecember 17, 2013 at 11:12 pm #20405
Hello: Ideally, water will never have the opportunity to sit and stagnate in a tank. With parallel plumbing, you likely would need to drain the unused tank (and of course turn off power to it). With series plumbing, you would heat with the downstream tank. Flow could be reverse with valving, but it would be complex.
I’ll guess from the photo that you have parallel plumbing. One can “temperature balance” tanks in a low tech way. To do this, plan on taking a big bath! Let water run until you feel cooler water coming from one tank before the other tank. (use the same hand to test temps) Then slightly reduce flow to the tank that had cooled first. Ideally, you want both heaters to go cold at the same time. An infrared thermometer can do this nicely if you happen to have one. 😎 Note that over time things change. Rust can build up in one line, throwing balance out the window, so periodic re-balancing is needed with parallel systems.
Yours, LarryDecember 18, 2013 at 8:23 am #20406
Thanks Larry. Sounds like I should have the plumber come back and reconfigure in series as it was originally!
AlDecember 19, 2013 at 11:09 pm #20407
Hello: I’m not really trying to cause trouble for your plumber. Parallel piping is the more common way of doing this, but it doesn’t work well with big variations in the hot water load. You don’t want water sitting too long in the tanks. Ideally the volume of a tank is used completely every day. This prevents the likelihood of odors or other bacterial problems. 😉
Yours, LarryDecember 25, 2013 at 1:19 pm #20410KurtVFParticipant
FWIW: I have two 40 gal tanks plumbed in parallel. I only need one. I alternate the tanks every 6 months (shut off the intake and turn the gas down to pilot) and after over 3 years no problems. Zero odor. During 2011 I was away for an entire year during a military deployment and left both tanks full and the pilots lit. I had someone run some water in the house every 3 months or so. The advice I got was to leave the tanks either full or BONE DRY. It was easier for me to leave them full and the pilots lit to prevent condensation. When I got home after a year no problems, no odor. I understand this might not work for everyone but so far it has worked for me and at least for my needs it seems to be the best solution. Might be worth a try……..
As far as the tanks becoming unbalanced: The plumbing to the two I have is exactly the same with equal lengths of pipe to each after they divide. I do not notice any change when I switch from one to another. Is the unbalancing something one can detect or is it something that only has an effect when the two tanks both have water flowing through them??December 25, 2013 at 2:37 pm #20411
Hello: “Is the unbalancing something one can detect or is it something that only has an effect when the two tanks both have water flowing through them??” To find the imbalance, or to tune the system to get it in balance, there has to be flow. The only two ways of finding this balance (that I know of) are to install flowmeters in the inlets to both heaters or to measure temperature coming out of both.
Even if the parallel system is installed right with equal lengths of pipe and fitting restriction, things can get out of balance as rust grows at tank connections or dielectric unions. Temperature balance seems the easier way to find out what the system is doing as it only requires touching the pipes to know when changes happen. What you don’t want is to run out of hot in one tank long before the other tank. This way you get only warm water in the shower which leads to “cool” people :P.
I like systems that don’t need that extra step of periodic balancing, just because usually it doesn’t get done and somebody has to learn to live with system quirkiness. If flow rate is important (eg: multiple showerheads) and you need flow through two tanks, then parallel piping is the clear choice.
Kurt, I think you’re a bit lucky to have no odor problems with your arrangement and usage. That’s fine…. just there are systems out there that would have problems in one or two weeks, from poor water quality. But that’s part of the fun with plumbing is that it’s soooo variable with so many changeable factors. No way to get bored doing plumbing!
Yours, LarryDecember 26, 2013 at 10:05 am #20412KurtVFParticipant
So just so I understand correctly, the balancing really only applies if you use both tanks together? Since I only use one tank at a time it wouldn’t really matter, would it??December 26, 2013 at 12:32 pm #20413
Hello and yes. Balancing is to prevent all the hot being used up from one tank before the other, because then you really don’t get the full benefit of both tanks. Using one tank at a time gets rid of the concern. 😉
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