Help me understand this setup

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Jeff H Young

I'm aware of the different lengths but think his drawing is likely mis representing the circ line being a cold.
I think a parallel system can tend to not pull equal not being a perfect world but didn't know if there is any unequallity that nothing at all will flow from the tank with greater restriction not so sure i buy that theory but admittedly uncertain .
So in Johns case I'm wondering what did he have to do to fix his issue

John Gayewski

Im aware of the differant lengthes but think his drawing is likely mis representing the circ line being a cold.
I think a parrael system can tend to not pull equal not being a perfect world but didnt know if there is any unequallity that nothing at all will flow from the tank with greater restriction not so sure i buy that theory but admitidly uncertain .
So in Johns case Im wondering what did he have to do to fix his issue
I actually just seperated the heaters and water piping for both apartments. I also gave them recirc.

Does anybody remember the bad old days when you'd take a shower then someone would flush the toilet and you'd get blasted with very cold water? You'd have to change the ratio on the shower to get hot water which is effectively balancing the flow.

It's not impossible that some could be coming from heater 2, but this setup does not give someone two heaters worth of hot water. Not even 1 and a quarter of any.

You'd have to measure the dynamic pressure at these heaters to know for sure, and it would be different with different combinations of fixtures running. It's possible with every fixture running the second heater would see some pressure drop and deposit some hot water into the system, but what I'm seeing, with one faucet running is all number 1.

wwhitney

Well-Known Member
It's not impossible that some could be coming from heater 2, but this setup does not give someone two heaters worth of hot water. Not even 1 and a quarter of any.
First, the OP says the drawing is not to scale, so for all we know their system is perfectly balanced.

Second, I showed you the math that says that if one path is 50% longer than the other, it will still provide 80% of the flow of the other; if one path is twice as long as the other, it will still provide 70% of the flow of the other.

So while the effect you are describing is real, I believe the disparity is not as large as you are saying.

Cheers, Wayne

Reach4

Well-Known Member
I think measuring the temperature of the hot pipes between the junction and the output of the respective heater while hot is being used would be a good measure of imbalance. Partially closing the valve to the heater supplying most of the heat could make the flows more equal.

An IR thermometer would be a tool that can measure the pipe temperatures.

Retired Defense Industry Engineer xxx
Personally, I think I'd run them in series versus parallel. The last tank would not get as much wear since it would mostly be being fed with hot water.

Jeff H Young

I have plumbed them both in series and parallel mainly on new builds can't really say they worked perfect usually wasn't there after the gas was turned on. but don't recall complaints on either method . I've heard arguments both ways for decades , I'm not convinced of either method superior.

Retired Defense Industry Engineer xxx
With them in parallel, each one gets emptied at the same time (hopefully). But, that also means that each one ends up only being able to output about 80% of their total volume prior to things starting to cool off, that means that 40% of your total hot water is inaccessible. If they are in series, you aren't filling the final one in the series with cold water, so you get its entire contents, and then only after the first one starts to cool off are you getting that output, so you're back to only losing about that 20%, and since it might still be slightly warmer for that last 20%, in reality, you'll probably get maybe another 10%, so only end up losing 10% of your total capacity in the sum of your two tanks. That does mean that the first tank will end up seeing more wear and tear, as the last one may only turn on to recover temp rather than heating up the whole thing until you need a big hot water draw.

Jeff H Young

With them in parallel, each one gets emptied at the same time (hopefully). But, that also means that each one ends up only being able to output about 80% of their total volume prior to things starting to cool off, that means that 40% of your total hot water is inaccessible. If they are in series, you aren't filling the final one in the series with cold water, so you get its entire contents, and then only after the first one starts to cool off are you getting that output, so you're back to only losing about that 20%, and since it might still be slightly warmer for that last 20%, in reality, you'll probably get maybe another 10%, so only end up losing 10% of your total capacity in the sum of your two tanks. That does mean that the first tank will end up seeing more wear and tear, as the last one may only turn on to recover temp rather than heating up the whole thing until you need a big hot water draw.
so you say both tanks empty the same (and I agree that's the plan) In other words when you use 40 gallons hot its 20 from each tank .
Accepting what you say that each tank will give 80 percent that means 20 percent is not available I think your theory might be right but the math is off by a bunch 2, 50 gallon tanks giving 80 percent hot means 80 percent or 80 gallons , How ever I'm not saying you'll get that much or not but going with your numbers . How you've figured it out to be a 40 percent loss ? you pull 40 gallons out of 2 heaters you've got 80 just wondering?

James Henry

How is tank 2 doing anything when tank 1 fills back up from the cold water supply pipe as soon as you turn a hot water faucet on?

wwhitney

Well-Known Member
How is tank 2 doing anything when tank 1 fills back up from the cold water supply pipe as soon as you turn a hot water faucet on?
How is tank 1 doing anything when tank 2 fills back up from the cold water supply as soon as you turn a hot water faucet on?

Cheers, Wayne

James Henry

They must both fill at the same time.

John Gayewski

They must both fill at the same time.
That's the problem tank 2 doesn't fill at the same time nor does it deplete at the same time. In hydronics it would be called a dead leg. Hydronics works with much smaller pressure differentials than plumbing so there could be some flow. Sometimes people fix dead legs with more power, Tim the tool man style,aka larger pump.

Retired Defense Industry Engineer xxx
Well, I didn't state it quite right...when you have two tanks in parallel, you effectively get 80%x2. When you have two tanks is series, it is effectively one tank, so you get to use all of one and only lose 20% of one of them. And, because you have twice the burner, the outlet of the first in line will be feeding warm water into the second for a bit, and you may gain a bit more total hot water. But, when in parallel, it's rare that they are perfectly balanced.

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Hey, wait a minute.

This is awkward, but...

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