Water heaters in parallel

[Jmcc64]

I've got (2) 50 gal water heaters installed in parallel. Is there an easy way to check whether heated water is being drawn from both tanks? the piping runs coming out the tops appear to be of the same length; everything looks symmetrical.
It's just that sometimes I don't think we're getting any more than 50 gal's of heated water before it runs out. I suppose one of them could have bad elements; they're over 1o yrs old.

 

[Plumbs]

Easiest way I can think of, if you don't have the right tools, would be to shut the power to one of them then see how long the hot water lasts. Then try the same with the other heater and see if there's a difference.
Or you could check the elements with a multimeter to see if they're within specs. There are plenty of videos on YouTube showing how to do that.

 

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[Jadnashua]

Running them in serial can help but the one furthest away from the points of use will likely wear out first. You can normally get at least 75% out of a single tank before the temperature starts to drop. With running them in parallel, that means 25 gallons out of the total if they're perfectly balanced. Running them in serial, you'd get 100% of one tank, and 75% of the second, so get an extra 12.5 gallons out of the system. In reality, maybe a bit more since the second tank would still be getting somewhat warmed water while they both would be heating water.

 

[Fitter30]

In theory equal length piping should give equal flow but reverse return ( first in last out) will take care of any difference.
https://forum.heatinghelp.com/discussion/163460/hot-water-tank-reverse-return

 

[WorthFlorida]

The sure way is to install a check valve at the hot water outlet with a temperature gauge on each unit. Trying to make everything as equal as possible to draw evenly from both is nearly impossible. If you know how to use a volt ohm meter you have to check the heating element (if it is electric) that both sets are working and know how to check that the thermostat are working correctly.

With two tanks in parallel, cold water draw from a fixture can pull the hot water from one tank in reverse to the other. It is not just the hot side connection but the cold water connections and fixtures.

This same question comes up every once in a while, parallel or series connection with two water heaters. The first question is why two tanks? The best fix and only one water heater is needed is to set the WH thermostat to 140 degrees and use a tempering valve and set the output to 120 degrees.

 

[Jmcc64]

The sure way is to install a check valve at the hot water outlet with a temperature gauge on each unit. Trying to make everything as equal as possible to draw evenly from both is nearly impossible. If you know how to use a volt ohm meter you have to check the heating element (if it is electric) that both sets are working and know how to check that the thermostat are working correctly.

With two tanks in parallel, cold water draw from a fixture can pull the hot water from one tank in reverse to the other. It is not just the hot side connection but the cold water connections and fixtures.

This same question comes up every once in a while, parallel or series connection with two water heaters. The first question is why two tanks? The best fix and only one water heater is needed is to set the WH thermostat to 140 degrees and use a tempering valve and set the output to 120 degrees.

2 tanks because of height restriction in the space and because my wife and 2 daughters can take loooong showers and baths. for my wife there is no such thing as too hot water temp.

 

[Jadnashua]

Code calls for the maximum outlet to be NGT 120-degrees except for certain devices like a dishwasher and washing machine. But, the actual storage temperature can be anything safe for your tank as long as you temper the output to 120. This means your tanks end up looking and acting like a larger reservoir of hot water.

 

[WorthFlorida]

With three women in a household, a coin operated water heater would be the only way to train them that hot water is not a given right. I grew up with three sisters and mom. One day my dad shut the water off while my oldest sister taking a usual too long of a shower. After that he won and my sister was more temperate with her shower time. Warning, that won't work with the wife.

About the only way to quickly know where the hot water is coming from, after about an hour of no water use so both tanks are at the set temperatures, place each of your hands on the hot water pipe at the WH and run the hot water from a fixture. The temperatures should feel about the same. If one seems to cool off faster, that tank may have a bad element. It is also possible that the calibration of one of the thermostat went to tilt and it turns off the element at a lower temperature.

Electric tanks have an upper and lower element and two thermostats. With a cold tank, the upper element is turned on by the upper thermostat. When it reaches it set temperature it switches off the top element and brings power to the lower element to heat the cold water entering from the bottom. Once it reaches temperature, the lower thermostat switches off the power. When water is drawn the lower thermostat will be switched on When the upper part of the tank gets too cold, the upper thermostat switches off the lower thermostat to power the upper thermostat. This sequence attempts to always deliver at least warm water if the demand exceeds the capacity of the WH.

When one element goes bad the results are different depending on which element went bad. If the bottom element is bad, only the top half will have hot water and the lower water warm. If it is just the top element is bad, the bottom element will heat the entire tank to temperature as long as no water is drawn. But as water is drawn and the upper thermostat switches on the upper element to heat the water, it cannot heat the water with a bad element and the lower thermostat will never turn on. Therefore, you can have one tank not providing heated water and thus cooling down the hot water from th eother tank.

 

[Jadnashua]

Ia parallel setup, each unit takes out the hot water demand equally. One gallon of cold water is pumped into the water heater for every gallon of hot water drawn from each unit.

Not necessarily true...depends on the relative length of the flow path and the number of fittings along the way...water will take the path of least resistance and that may not be evenly from two tanks in parallel.

 

[Jmcc64]

With three women in a household, a coin operated water heater would be the only way to train them that hot water is not a given right. I grew up with three sisters and mom. One day my dad shut the water off while my oldest sister taking a usual too long of a shower. After that he won and my sister was more temperate with her shower time. Warning, that won't work with the wife.

About the only way to quickly know where the hot water is coming from, after about an hour of no water use so both tanks are at the set temperatures, place each of your hands on the hot water pipe at the WH and run the hot water from a fixture. The temperatures should feel about the same. If one seems to cool off faster, that tank may have a bad element. It is also possible that the calibration of one of the thermostat went to tilt and it turns off the element at a lower temperature.

I tried something like this tonight when I got home. Both outlet lines cold, had wife turn on hot water in tub. One outlet pipe got pretty hot while the other.....not so much. Warm but not as hot as the other. So that maybe something to look at as a starting point.

 

[Jadnashua]

It doesn't take a whole lot of differences in the path for the outlet of one tank to supercede the other. You might be able to help balance things a bit better if you added a valve on the one that's now supplying the most water, adding a slight restriction that would force flow though the other.

It will work more reliably if you were to replumb them in serial rather than parallel.

 

[Jeff H Young]

Easiest way I can think of, if you don't have the right tools, would be to shut the power to one of them then see how long the hot water lasts. Then try the same with the other heater and see if there's a difference.
Or you could check the elements with a multimeter to see if they're within specs. There are plenty of videos on YouTube showing how to do that.

turn power off and see how long it takes to get cold? you do that and if it takes a differant amount of time its not flowing equal? assuming heaters are same temp and you have good feel for the coolness. Sounds like it will get you in ball park to find a gross differance on a test anyone can do.

 

[Jmcc64]

Ok. Hopefully final update. Looked at the upper stat and pushed the reset button and it "sounded" like a pretty good click. Element checked out ok for continuity and everything "looked" pretty clean. Lower panel was different story. the plastic cover over the stat had melted to the screws but the element checked out fine, so I replaced the thermostat out of caution and we'll see how it goes.

 

[Lucyyyyy]

A one-year-old element can not be as old as it doesn’t work!

In a parallel setup, each unit takes out the hot water demand equally. One gallon of cold water is pumped into the water heater for every gallon of hot water drawn from each unit. Then, each heater conducts the same amount of work to heat the cold water.

I think something goes wrong with circuits at first installation. You can read more here or get online advice easily and stop to be charged with no reason.