I just replaced the elements in my 80 gal hot water heater. It's wired
on a 240V 30A #10 circuit. The two elements are 3800 watts and 3800
lower with optional bus bar to 5500 watts. I did the math while I was
working and if they both fire at the same time, that's over 30 amps,
especially if I jumper to 5500 watts on the bottom.
Am I wrong about them both firing at the same time when the recovery
element comes on? Or is there something at work here that I don't
understand about hot water heaters? I asked a buddy of mine who is an
electrician and he says they always wire them 240v 30A #10 for
Once the water is heated up, it's hot.
Of course water loses thermal energy and its temperature falls, but
then the water is no longer hot. It is cool, maybe warm at best, and
therefore needs to be heated up again to make it hot.
A water heater heats cold, cool, or warm water. Calling it a "cold,
cool, and warm water heater" would get a little long in the tooth so
it is simply called a WATER HEATER.
Of course, once again you're wrong. The water heater doesn't heat up the
water and then let it cool way down. It only lets the temp drop a few
degrees, and then cycles the elements (or burner, if gas) back on to
maintain the temperature. Otherwise, when you turned on the hot faucet,
you'd never know if you'd get hot water, warm water or cool water.
The upper theromstat determines whether the upper or lower element
gets power, but in the lower element of many WHs ther is a bus one can
use to,optionally, connect two "filaments", actual heating wires,
within one "element". The owner can use the first one, both, or
afaic, the second one only. Surely if the second one burns out he
can continue using only the first one, which is the way it comes wired
in the first place.
On Fri, 16 Apr 2010 06:55:38 -0700 (PDT), jamesgangnc
I'm sure the purpose is not so one can be a spare, but what does their
purpose have to do with me? Why can't I just switch elements when one
burns out. If 3800 is enough for some people and the second part of
that unit burns out, why can't I go back to 3800?
Thanks boys... makes me feel better. Another question then:
Should the top element (adjustable only behind the panel) be set at
roughly the same temp as the lower (externally adjustable) element?
If the top is supposed to be there for "recovery", I'm thinking that
you'd want it to come on as soon as the temp starts to drop below the
level you like the hot water at (set by the lower thermostat). Is
there any reason you would NOT want it to come on fairly soon? I could
see some electricity savings if it stays off, but if the tank temp has
dropped below the requested lower thermostat level (which is going to
happen quickly when the cold water starts coming in down there), isn't
the lower element going to come on anyway... so you might as well have
the upper one come on?
Also, why would the lower element have the dual 3800/5500 choice...
when the upper one is the one that will have to heat water very
quickly in a recovery situation?
The upper comes on first. The lower is wired to not come on until the
water around the upper thermostat has reached its setting
Although the cold water comes in at the bottom, the water leaves at
the top, so they want the water at the top to be hot as soon as
possible. When it reaches the temp it is set for, the thermostat
turns off the top element and turns on the bottom, at whatever wattage
you have that part set for.
In most home usage patterns, I think the lower one does the bulk of
the work. If you used hot water ALL the time, the top element would
be on all the time, but since you're not running a factory that uses
hot water all the time, soon you stop taking a shower, fililng the
bath, washing the clothes, or the dishes, and soon after that, the
water at the top reaches the thermstat temp.
Then the bottom element turns on and heats the water below the top
level, about 80 or 90% of the water in the tank, I'm guessing. That
water is even colder, because hot water rises and cold water sinks,
and because the outlet for the cold water input is at the bottom of
the tank. So I think the lower element does way more than half of
The water cools slowly even when not used. I suppose it's the bottom
element that goes on when it cools enough, but maybe not.
The advantage of having both filaments at the bottom connected at once
is that it will finish heating faster. I'm not sure what the
disadvantage is but I'm sure there is at least one, or they would come
wired the other way. I'll bet the element lasts longer when it
doesn't get too hot. Maybe you might need heavier wires for 5500
watts? Maybe something else?
My previous water heater had an LED that was on when the upper element
was on. I guess just so people could see that they were getting what
the advertising said they were getting. I think it was an advertised
feature when I bought that one**, but by now maybe it's so standard
**It was Sears but it was identical to AOSmith that came with the
house in 1979.
The current WH doesn't have the LED because, I think, they filled all
the empty spaces around the thermostats each with a chunk of
Anyhow, sometimes I watched, and the red led and the upper element
came on when water was used to fill the bathtub for example. It would
turn off maybe 2 to 5 minutes after I got to the basement. I'm sure
the lower element went on then.
IIRC and I pretty sure I do, both thermostats should be set at the
same temp. They come that way.
I've bought two wh from sears and the new one sure seems to be set not
as hot. Maybe this is so it can be green. I like that it's cooler
because I can't scald myself, but it is more than hot enough for what
I consider a hot bath. The problem for me is that if I add even a
little too much cold water, the hot water isn't hot enough to get the
tub to the right temperature. I made the wh a little hotter, but
maybe I need to go higher.
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