I currently have a standard 40 gallon electric water heater on a 30
amp breaker. The panel is 100A service which also services an electric
dryer. I was thinking about getting a tankless water heater to save
space, but after reading some electrical specs on these units, it
seems I would have some issues with the electric.
I have 1 bathroom and 1 kitchen and a washer. From the calculations I
would need at least a 5 gpm unit.
If you look at the specs for the Rheem units, the RT18 needs 2
seperate 40A circuits, with maximum power being 75 amps.
Obviously my panel cannot support that. I could maybe drop to the RT9
unit that requires 1- 40A breaker, but I'm concerned it might be
undersized at 3 GPM, and also concerned that it uses 38 amps. If my
dryer is on, thats another 26 amps, and my 220V water pump using 5
amps, totaling about 70 amps.
That leaves me with about 30 amps to spare.
So I could either upgrade my panel, or just stick with what I have.
This is for a seasonal home in the summer. Just wondering what
everyone else thinks I should do.
You can easily "do the math" and determine EXACTLY what the temperature
rise is when you run 40 amps at 240 volts through a water heater.
All that really matters is the temperature of the cold water coming in
and the flow rate.
If you are "marginal" you can help by reducing the flow rate and if your
cold water coming from outside is "too cold" you might want to help it
along by running it around the basement. It's important to "temper" the
cold water to the shower mixing valve since the warmer that water is,
the less "hot" water you will need for a comfortable shower.
I can give you a "data" point. We have a conventional electric water
heater. Even when I "run out" of hot water, if I run 100% hot water
into the shower, it's tolerable. Bottom line is that it depends on
just how hot you want your shower.
You first task is to: 1) measure the temperature of the cold water;
and 2) "do the math" and determine the temperature rise at various flow
rates; & 3) decide whether it's "gud enuf."
The only "justification" for a demand type hot water heater is to "save
energy" by not keeping 30/40 gallons of hot water sitting around &
heating up the basement. You can "save" much of that energy by adding
insulation to the heater, installing that gadget that prevent
circulation of the hot water above the heater (I think it's just a
"leaky" check valve), and if your circumstances permit, just shutting
down the water heater when you don't need it.
Frankly, the cost of a new panel or the equipment and wiring costs of a
"demand" WH will take years to recover.
I think standard breakers really are not meant to be used as
switches. You can get breakers that are specifically rated for it. I
found it more convenient to install a real switch next to our
thermostat which we change when we leave too.
*I would look into a solar water heater or something to boost the
temperature of the water going into your current water heater.
GPM tells how large the water pipe that goes through the water heater is, n
ot the actually heating capacity. You have to pay attention to watts. An el
ectric tankless water heater has perfect efficiency so there is a strict ma
ths that tells you how hot it can make the water. What you need to know is
how much water flow you are going to require, how hot is good enough for yo
u and you incoming tap water temperature. This explains it much better:
If you decided to do tankless, you definitely need to get something bigger
than you think you need. There is going to be some heat loss in the pipes e
tc. so you can never get a too powerful electric tankless water heater. Tha
t's why many people say tankless sucks. They get a small device and it does
n't heat enough.
I doubt Rheem RT9 will do any good even for a single person, unless you are
in a really hot region. 15 watts is the minimum for tankless electric.
On Thursday, September 18, 2014 12:20:48 AM UTC-4, sol wrote:
not the actually heating capacity. You have to pay attention to watts. An
electric tankless water heater has perfect efficiency so there is a strict
maths that tells you how hot it can make the water. What you need to know i
s how much water flow you are going to require, how hot is good enough for
you and you incoming tap water temperature. This explains it much better:
r than you think you need. There is going to be some heat loss in the pipes
etc. so you can never get a too powerful electric tankless water heater. T
hat's why many people say tankless sucks. They get a small device and it do
esn't heat enough.
And the flip side is that a big one takes so many amps that it may
require upgrading the panel/service. Factor that in with the much lower
cost of an electric tank type unit and the tankless doesn;t look so
good. Also, many places have time of day metering now. If you can run
the electric tank WH during off peak, at night, etc, it can save a lot
in operating costs.
re in a really hot region. 15 watts is the minimum for tankless electric.
You left out the K in Kwatts. I can see smaller ones used for special
applications, like if you had just a sink somewhere in a building that's
rarely used. That could be a good application for tankless and a small
one would fit. But I agree that you need a decent size one to do even
one bathroom with shower. Whole house gets worse. If you want tankless,
gas tankless looks much better, but I'm not a fan of those either, for
well known reasons, high initial cost being the main one.
for electric tankless figure at minimum 200 amps just to heat water, plus a different panel of 200 amps for everything else. at least a 100 amps but you might as well go 200 amps.
this will require 400 amps total, need new service drop and the power company may need to do upgrades on their side of the meter....
the payback is never...
a friend looked into this, he called it going green.
all in over 15 grand.:(
On Thu, 18 Sep 2014 07:32:53 -0700 (PDT), trader_4
A 15kw heater (62 amps at 240v) will give you about 45 degrees above
the input water temperature at 3 gallons a minute.
Even with the most efficient water saver shower head (jump around to
get wet), you are probably getting a cold shower in the winter and if
someone turns on the hot water in the kitchen you will be freezing. My
brother in law needed 3 big propane fired units to have satisfactory
hot water in his house.
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