I bought a home a few months ago and didn't even think to look at the hot
A friend suggested today that I set the temperatures differentially; and
when I asked why, I realized I had no idea why or to what advantage two
hot water heaters would be set up in serial connections. (I'd have used
one for the teen's bathroom, and another, in parallel, for the rest of
Anyway, what's the THEORY and RATIONALE for having two hot water heaters
- What's the main advantage (is is simply gallonage?)
- What is the main benefit?
- What is the key drawbacks?
And, most importantly:
- Would you set the temperatures differently on them or the same?
the hot water from #1 heater going into the second heater (in
series)doesn't get heated unless it's temp is lower than what the
thermostat is set at.
and available volume or flow rate doesn't increase,because a tank can only
flow so much water,and that flow has to go thru the 2nd tank.
a parallel connection allows both tanks to add to the water supply(double
flow) and both tanks do the heating.
I doubt a series connection would pass inspection.
And I explained why.
Along with why a serial connection is not used.
If you don't know what a serial connection is,how can you comment on a
you don't know the difference,if you don't know what a serial connection
On Mon, 14 Mar 2011 21:12:47 -0500, Jim Yanik wrote:
Well now I'm thoroughly confused.
It sure LOOKS like a serial connection.
The cold water from the well pressure system goes into the first hot
water tank and out of the heat pipe of the first tank it goes into the
cold inlet of the second tank and out of the heat pipe of the second tank
it goes to the house with a recirculating motor somewhere on that final
output (I can see the recirculating pump and I can hear it but I don't
know exactly how it works.)
So, all that LOOKS serial. The house was built to code I would think, at
Plus there is that web site that explains serial hookups. So are you SURE
that serial hookups would not be to code? Why?
It is not that uncommon, so MUST pass inspection. It uses the same
theory as the dual element electric water heater, where the bottom
element heats the cold water that comes from the mains or well, and
the top element heats the warmed water. It will more than double the
amount of hot water available.
Which is it? Series or parallel? Or do you want to go from parallel to
I worked in a restaurant that had 5 gas heaters in series. The last one
in line was hot all the time. When it dropped to a certain temp, it
stayed on and turned on the previous heater so it would be suppling warm
water to the last heater and so on down the line. The owner was a
retired engineer. The purpose was to only heat one tank when that's all
that was needed, and as the need for more hot water rose, the other
heaters kicked on as needed. You could get over 20 gallons of hot water
a minute continuous, never letting the temp fall below... I think it was
On Mon, 14 Mar 2011 17:31:28 -0400, Tony Miklos wrote:
My mistake for not being clear.
They are clearly in series.
The well pumps the cold water which goes to a four-foot high blue steel
bladder tank which goes to the first 50 gallon hot water heater which
goes to the second 50 gallon hot water heater in series which somehow
goes to a hot-water recirculation motor about the size of a small bench
grinder motor ... which goes to the bathrooms, laundry room, and kitchen.
My question is why (I'm slowly learning why) and what to set the
temperature at (since it's currently set the same for both at about 130
degrees or so).
I have seen the tandem system used only once, by a co-worker.
He had a big unit, working on night-current only(very cheap in our
country), and a small unit after it, using day- and night-current.
The small unit would quickly heat(big heating element), and would be fed
with cooler water later in the day.
That combi had a rather constant water temperature for a
Thermostats were the same on both machines.
See http://www.chinawinds.co.uk/diy_tips/installation_series_and_parallel.html .
Basically, in series connection, the first one (which gets the cold
water) normally does most of the work. The second one, which normally
gets pre-heated water, does much less work. During periods of low
draw, it may do no work at all, if the inlet water is already at its
So if they're in series, you might consider reducing the setpoint of
the first one, to balance the workload of the two units, ie, have them
each heat the water by the same number of degrees. That's assuming
there is some advantage to doing so. Presumably the lifetime of the
heating elements (or burners) is basically so many hours of actually
making heat. Offhand I can't see how the lifetime of the tank or the
anodes, would vary by workload. Actually I've never heard of a burner
failing, and elements and anodes are replaceable, so maybe workload
doesn't matter much.
Arguably, keeping one of them at a lower setpoint may reduce standby
losses from it, too.
Lots of hot water when you need it.
I have only been in one house plumbed that way. It was an older couple who
only turned on the breaker for the first unit in the series when the family
came to visit. They did claim that the tempering factor of bringing the
water into the basement pre-warmed it a little in the winter. That seems
somewhat reasonable to me. The rest of the time the one was just fine for
If I were running both at the same time, all the time, I would set the
first in the series a little lower, as low as fit my needs. The second one
would be set to deliver water at the temp I wanted. I would do this to save
the standby loss on the first unit. Unless you are filling the big tub or
have a large family 50 gallons is adequate for most needs.
Please come visit http://www.househomerepair.com
I might even turn OFF the first hot water heater (or set it to something
really low, like 50 degrees or something).
The only one who uses a lot of hot water is the teenager (and that kid
can freeze because there is no reason to take an hour-long shower anyway).
I wonder if this will affect the hot-water recirculating system adversely
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