piping 2 water heaters in series

mikedo

is their any drawbacks to piping 2 fifty gallon water heaters in series. i have limited height and 1" feed for cold water

DZoro

nothing wrong with it, if you have the need for 100 gallons of hot water on a constant basis. May want to consider a on demand system.

hot_rod

No problem with series. We commonly did that with vacation homes, turn the 1'st one to vacation setting until the home is at full occupancy.

The first tank will see most of the mineral and sediment build up.

Ironman

Are we talking gas or electric?

If it’s gas, the second one will see a decrease in efficiency because of the hotter water temp entering it.

JohnNY

I've never been a fan. Pipe them in parallel and they'll wear evenly and at half the demand put on the first tank in the series piping configuration.

hot_rod

If you do want to pipe parallel 3 piping choices are, reverse return, "moose antler, or add a balance valve on both tanks to balance draw evenly. The balance valve option may help with your piping limitation issue.

This drawing happens to be indirect with balance on the coil and potable water side.

Larry Weingarten

Hello, My experience with parallel piping is often they get thrown out of balance just by corrosion or rust happening where nipples are screwed into the tanks or from dielectrics. If you can temperature balance the system periodically, parallel is fine. Otherwise, (as long as flow remains OK) series with bypass valves on each tank is my preferred way.

Yours, Larry

ps, Water in my area can get pretty bad and that has everything to do with the sort of problems I see. If you have good, not very conductive water, there may be no problem down the road, going parallel.

hot_rod

Larry Weingarten said:

Hello, My experience with parallel piping is often they get thrown out of balance just by corrosion or rust happening where nipples are screwed into the tanks or from dielectrics. If you can temperature balance the system periodically, parallel is fine. Otherwise, (as long as flow remains OK) series with bypass valves on each tank is my preferred way.

Yours, Larry

ps, Water in my area can get pretty bad and that has everything to do with the sort of problems I see. If you have good, not very conductive water, there may be no problem down the road, going parallel.

Good point Larry, dielectric unions are notorious for corroding closed. With a 132 Quicksetter you could observe and re-balance from time to time

mikedo

thanks I'm just going to pipe them in series

JohnNY

hot rod said:

With a 132 Quicksetter you could observe and re-balance from time to time

Or you can pipe them in parallel and never think about it again.

@mikedo You're doing yourself a disservice by going with series piping. But whatever.

GBart

I was taught that parallel was the only way, there is reference material to back this up. In parallel the supply and outlet piping to each unit must be exactly the same and they must be equal units. In series the first unit typically does all the work, this can work if you are doing solar-another water heater, gas fired feeding electric, etc or if you have non matching size tanks. Piping in series usually causes the first tank to fail way before the other.

Another option for series is a water heater piped to a aqua-booster to increase storage using the first heater to supply the aqua-booster.

http://www.texasinspector.com/files/Water-Heater-Plumbing.pdf

hot_rod

GBart said:

I was taught that parallel was the only way, there is reference material to back this up. In parallel the supply and outlet piping to each unit must be exactly the same and they must be equal units. In series the first unit typically does all the work, this can work if you are doing solar-another water heater, gas fired feeding electric, etc or if you have non matching size tanks. Piping in series usually causes the first tank to fail way before the other.

Another option for series is a water heater piped to a aqua-booster to increase storage using the first heater to supply the aqua-booster.

http://www.texasinspector.com/files/Water-Heater-Plumbing.pdf

If the first tanks fails earlier, seems the second tank lasts much longer, isn't it sixes at that point ?

Any data to support the first tank failing way before the second?

In our rental/resort applications series made more sense and I don't recall the failure rate you suggest?

I'd highly encourage HW users to run tanks at 140 for bacteria reasons, so I doubt efficiency would be much different between first and second tank, we are talking 70% efficient appliances typically with standard tank heaters.

I hate seeing bullhead tees, even on domestic water piping, as the parallel drawing shows. It doesn't take much flow resistance, as Larry mentioned to put them out of "balance"

Series is nicer for recirc as you just circulate thru one tank.

Seems like Rheem is fine with either piping method.

GBart

The first one does all the work, ergo it has more run time ergo it fails first, it's in several documents on line

jumper

GBart said:

The first one does all the work, ergo it has more run time ergo it fails first, it's in several documents on line

all depends. First one runs cooler? Series is often said to be no no but I don't see why.

hot_rod

GBart mentioned parallel piping is the only way and you have reference material to back it up?

The Rheem doc you attached seems to show series as an option? Although it shows a gas and electric In series, much different recovery rate tanks.

Generally two tanks are used to cover large dump loads like filling a 100 gallon soaking tub for example, or multiple showers running at the same time, as in ski resort rental properties.

So both tanks get pulled down to 100 f or lower. Under that type of use pattern I don’t see a much shorter life expectancy in the first tank. Consider tanks are engineered to a 6-7 year warranty these days.

JohnNY

Why is there even a discussion on this? When you install multiple tanks/boilers/etc in parallel and fire them up from a cold start, you can watch and hear them fire up and shut down within seconds of each other. Forget about balancing valves. They're not needed. Isolation valves will do, and only if you want to include them. Setting the tanks at different temperatures is a guess at what's going to work best.
Install them in parallel, same temperature, full flow (ie. half to each, naturally occurring), and you're done.