Adding a second water heater

[Qapla]

Our house came with a 40 gal water heater. We have 3 bathrooms and four daughters. two of the baths are on one end of the home and the Master is on the other end with the kitchen in between but on the other side of the house (baths are near back while kitchen is near front).

We had an existing 40 gal water heater from our old house (it was only about a year old) so I installed that in the master area. Well, it did some odd things. Seems when the baths on the other end of the house were used it pulled the hot water from the master tank and when we used the master shower, it pulled the water from the other tank. I tried backflow preventers on the outflow but it did not help.

In the end, I had to disconnect the hot at the master tank coming from the other tank and use the master tank for ONLY the master and let the other one handle the rest of the house. It works great!

We have to replace the element in our tanks on a somewhat regular basis due to lime/calcium buildup. After some time we also had to start replacing the controls on the tank that came with the house so our oldest daughter decided to buy a new tank. She went with the largest that would fit the space. It is 80 gallons. Believe it or not, our electric bill went down.

 

[Aquamoose]

Or this...

It will teach them the value of water conservation, economics, fairness, work ethics all while making money!

 

[GLyford]

Say you've got two 50-gal tanks.

Right, for 100 gallons AT TEMPERATURE.

You use 50 gallons of hot water for your shower. In series, the first heater has to heat up the entire 50 gallons again while the second tank experiences no load. In parallel, both tanks have to heat up 25 gallons.

Either way, you've got 50 gallons to heat, and that's going to take X amount of BTUs to heat it, regardless of whether one unit is doing all the heating or two units are each doing half the heating.

Yes, the energy used is the same, but that is not the only issue...part of the issue is the amount of hot water available at the moment of demand. With parallel tanks you are pulling out hot, but they are being refilled with cold, cooling off all the water in both tanks. So by the end of the 50 gallons of use, the water in both tanks is half as warm. Stratification helps some, but it is still mixing in and cooling off.

In series, the water drawing into the 1st tank being warm to start with means that the chilling effect of the cold water is delayed, and the water stays hotter to the end of your 50 gallons. But if you keep going from there to the end of the 100 gallons, yes it's all cold and it doesn't matter.

So to my mind at least, hooking in series is a way to mess with the timing of availability of hot water, not total energy use.

 

[Gary Fowler]

Right, for 100 gallons AT TEMPERATURE.



Yes, the energy used is the same, but that is not the only issue...part of the issue is the amount of hot water available at the moment of demand. With parallel tanks you are putting out hot, but they are being refilled with cold, cooling off all the water in both tanks. So by the end of the 50 gallons of use, the water in both tanks is half as warm. Stratification helps some, but it is still mixing in and cooling off.

In series, the water drawing into the 1st tank being warm to start with means that the chilling effect of the cold water is delayed, and the water stays hotter to the end of your 50 gallons. But if you keep going from there to the end of the 100 gallons, yes it's all cold and it doesn't matter.

So to my mind at least, hooking in series is a way to mess with the timing of availability of hot water, not total energy use.

Every double installed hot water tank I have seen is piped in series so the first is preheating and the second heats to final temp. Energy used is the same but the amount of hot water you can get is almost unlimited. Dual hot water heaters can heat water from a 3/4" inlet just about as fast as it can run thru.

 

[PILOON]

Some good humor in here as well as possible solutions.

It comes to mind that I recall reading that tankless units are efficient to raise temp by about 40 deg or so and not from ground water temp to near boiling.
Perhaps the tank at lower setting combined with tankless unit close to shower could be a solution but that still calls for HD electrical circuit.

The one I liked best was the coin operated timer, but that'll never get you rich besides you'd simply be increasing their allowances.

 

[ovrszd]

Lot of chest thumping in this thread....

Some very good ideas as well.... Just gotta sort the differences.

 

[Aquamoose]

Some good humor in here as well as possible solutions.

It comes to mind that I recall reading that tankless units are efficient to raise temp by about 40 deg or so and not from ground water temp to near boiling.
Perhaps the tank at lower setting combined with tankless unit close to shower could be a solution but that still calls for HD electrical circuit.

The one I liked best was the coin operated timer, but that'll never get you rich besides you'd simply be increasing their allowances.

Figured I'd get some humor in this somehow.

I understand your precedent. Like you, I have a large household in my 6k sq ft house. It has two 50g tanks plumbed in series but on natural gas so I couldn't help too much with regards to that BUT,

I once had an electric water heater setup in my shop to heat the radiant floor that would quickly run out of hot water. I took it out (sold it practically new so little loss) and installed a shoe box sized Rheem instant water heater on the wall and I'm far pleased with how well this contraption worked. My unit has a knob which you can dial in how much hotter the water gets. I had it on high, which feels like it's on "Lava" setting but it's set much lower than that because I require a constant temps in the 76° range. HOWEVER,

You're correct that tankless simply raises the water temps and some people fail to recognize the shortcomings from very cold climates. If you have near freezing water, you'd need a bigger unit. There's calculators on the internet that can help you size the right unit if you're inclined to investigate. For sure, prices have come down significantly lately so the benefits may be enough for you to go that route.

Perhaps a few brochures on coin-op showers laying around the house just might do the ticket to get their act together ;-). If I didn't have two tanks, I'd just set a countdown timer in the bathroom. If it goes off, the kids would risk getting a dump of ice water (and their allowance gets donated to charity). Seriously! There's so many creative ways.


Since you can't commit to running another power for the second tank, I should suggest that you look into the tankless idea.

 

[xtn]

Every double installed hot water tank I have seen is piped in series so the first is preheating and the second heats to final temp. Energy used is the same but the amount of hot water you can get is almost unlimited. Dual hot water heaters can heat water from a 3/4" inlet just about as fast as it can run thru.

You can get the same result running them in parallel. Either way, you've got twice the BTUs going into the water on it's way through as you would have with a single tank. Cold supply water will come out the other end with the same total temperature rise in either configuration. Well, actually, the parallel setup has the advantage here because both of them are starting with cold water, whereas when in series the second tank will be starting with "half warmed" water resulting in slightly less efficient heat transfer in the second tank. But I'm sure that difference would not be noticeable to the person taking a shower.

 

[xtn]

Every double installed hot water tank I have seen is piped in series so the first is preheating and the second heats to final temp. Energy used is the same but the amount of hot water you can get is almost unlimited. Dual hot water heaters can heat water from a 3/4" inlet just about as fast as it can run thru.

Well, that depends on their BTU output size, of course. And of course it can be true for both a series setup and for a parallel setup. For a given water flow...with a series setup the water gets to go through twice, but at full speed...with a parallel setup it's only going through one or the other, but it's in there being heated twice as long. The result at the shower head is the same.

The only really valid reason to pick series or parallel is for serviceability, and I think parallel has the edge unless you want to put in bypass lines/valves on the series setup, in which case it becomes a moot point.

 

[bobmisi]

I just installed my first on demand water heater in my new building and it is the way to go. Cost about a thousand dollars, but it WILL end your hot water shortage problem once and for all.