Mysterious lack of hot water

[potatosalad]

Evening all,
I have two parallel electric, 50 gal, 220v-4500w water heaters. They are identical in these specs and brand name (Reliant) and were installed at the same time. Age is approximately 1.5 years.

Problem: At the end of the day, and only at the end of the day (8pm or so), hot water is running out. This is noticed when filling a large bathtub. Never with a shower. Once noticed and all hot water turned off, the system will produce plenty of hot water after 20 minutes. Both heaters can be heard heating.

Knowns:
-There is an hour sometimes 2 hours of delay from the last big demand of hot water till the filling of the tub.
- One 30 amp breaker for one of the heaters was recently replaced due to arcing with the old breaker. Second breaker is sound but not replaced. These breakers are checked often.
- Both elements in each tank were checked for continuity. The readings were from 11.6 to 12.5 ohms for all 4 elements.
- It's not the valves in the tub control stems. As soon as water runs out, we run a different sink or shower and still no hot water.
- both tanks have been drained once.

I am at the point of starting to replace elements one at a time to see if that does it. Other than that, I am just stumped.

It seems tied to filling that tub. We can run back to back showers, 3 sometimes 4 of them, and not have an issue.

What am I missing? Any recommendations appreciated.

 

[Twowaxhack]

What temp do you have the thermostats set to ? How big is the tub ? What’s the temp of your cold water ?

 

[Twowaxhack]

I’d love to see some good pics of the piping at the top of the water heaters.

I’d like you to check the amp draw of each water heater element with a clamp on meter. Divide the element wattage by the measured voltage and see if it matches your clamp on amp meter amp reading.

 

[potatosalad]

What temp do you have the thermostats set to ? How big is the tub ? What’s the temp of your cold water ?

Heater set to 120. Tub is single person. A 6 foot + person can lay with just head above water without bending legs, but I would estimate it holds at least 40 gal. Cold water is from well. I would not say it's exceptionally cold.

For the amp draw, do you mean take the reading from the wires at the element?

Thanks for the input.

 

[Twowaxhack]

Heater set to 120. Tub is single person. A 6 foot + person can lay with just head above water without bending legs, but I would estimate it holds at least 40 gal. Cold water is from well. I would not say it's exceptionally cold.

For the amp draw, do you mean take the reading from the wires at the element?

Thanks for the input.

Yes, check amp draw at each element while it’s firing. Should be close to 18- 20 amps

The piping of the water heaters is very important when piped in parallel. I’d like to see the piping.

 

[potatosalad]

Sorry for delay. I am traveling so request was relayed. This was the image sent. How is the piping important? We get hot water so it 'works' (in my mind). But obviously something is off. Would not have guessed piping.

 

[Twowaxhack]

That explains it. That set up will never work in parallel.

Convert that piping to series. Trust me, I do this for a living

 

[potatosalad]

I agree it looks goofy. Never wanted to touch it before now. Why is it bad? It's hard to find good (trustworthy) examples of what parallel is supposed to look like and why it should look that way.

 

[Twowaxhack]

I agree it looks goofy. Never wanted to touch it before now. Why is it bad? It's hard to find good (trustworthy) examples of what parallel is supposed to look like and why it should look that way.

First off the heaters are not identical. So it would never draw down equally between the two heaters. One’s going to do most of the work until it’s depleted then it’ll work against your other heater by mixing in cold water.

The flow will not be balanced.


Even if the heaters were identical the piping you have would cause the same problem. One heater would do most of the work and then start diluting the other water heaters hot out flow by mixing in cold from the depleted tank.

The hot and cold piping must be equal lengths split between the two water heaters.


The answer to correct all this is pipe it in series. It’s easy and you’d get the full capacity for the equipment you have .

I’ve corrected at least one illustration of incorrect parallel water heater piping on the internet, there is bad info out there.

 

[Twowaxhack]

Pipe it in series to make a long story short. Trust me.

 

[potatosalad]

Interesting. So just having heaters that are the same capacity and wattage isn't sufficient and the fact that one is short and fat and the other tall and skinny has that big of an impact? That's frustrating.

Well, when these need to be replaced, I'll be putting in two identical, in every way, heaters.

Won't a serial setup over tax the the first in series heater? Or am I over thinking it?

Thank you for the explanation. Saved me wasting time and money on copper pipe.

 

[wpns]

That's frustrating

That’s physics.

Series _will_ use one more than the other, but won’t ‘overtax’ it.

 

[Twowaxhack]

Interesting. So just having heaters that are the same capacity and wattage isn't sufficient and the fact that one is short and fat and the other tall and skinny has that big of an impact? That's frustrating.

Well, when these need to be replaced, I'll be putting in two identical, in every way, heaters.

Won't a serial setup over tax the the first in series heater? Or am I over thinking it?

Thank you for the explanation. Saved me wasting time and money on copper pipe.

The first heater in the series will do more work. That’s the way the cookie crumbles.

But the way you have it, you’re not reaping the full benefit of the two water heaters you have.

Yes, having different heaters will screw the “ draw down “ and one heater will do more work and when it’s depleted it’ll still be sending cold water to dilute the hot from the other heater. Bad bad bad.

Series piping is the way to solve your problems.