I don't believe it's accurate to say these tests were designed by the
industry. The manufacturers of water heaters certainly gave there
opinions and suggestions, but the actual test standards were arrived
at by the EPA. And different manufacturers have different opinions
of how the various water heaters should be tested. They were not even
close to being all in agreement.
However, I do agree with most of what you posted. Tests have to
assume some type of typical usage to come up with a way to do the
tests. And just like with cars, your mileage may vary, especially
if your usage is substantially different than the tests. And once
the tests are set in place, manufacturers will start to tweak there
designs to play the spec game. That's why I wouldn't go crazy trying
to figure this out to the last decimal place.
When I needed a new water heater, I went with another 50 gal unit,
which was what I already had. I did look at the energy efficieny
ratings and concluded that for my usage an average unit would be
fine. I went down to HD, bought it and installed it in one day. It
has a eff rating of .56, and cost me I think about $300 7 years ago.
I wasn't gonna lose sleep worrying over whether a .58 or .61 was gonna
make enough difference to be worth it.
I did get a 10 year warranty, which came in handy about 2 years ago.
The thermocouple went and State, who was the manufacturer, had a new
one here in 2 days for free.
No, the tests are done per EPA rules and specs by an independent
Now, on the other hand, those tests are performed under a certain set
of criteria based on an estimate of how the water heater would
actually be used. I would say the difference in how someone will
actually uses it in practice as compared to how it was tested, could
easily outweigh small differences in the recorded test data under the
controlled conditions. I would bet that a heater rated at an eff of .
61 vs one at .58 could easily be a wash or even upside down in actual
use. Same thing for the first hour rating.
In other words, over analyzing this whole thing is likely a waste of
time. Even the above payback analysis is flawed, because it ignores
the time value of money. Laying out $135 today and getting it back
over the next 6 years doesn't account for the fact that the money
could be earning a return. Or if you put the heater on a credit card
and pay interest, even for a short time, and the perceived savings are
gone. Take any of that into account and the difference between these
On Wed, 13 Feb 2008 06:16:37 -0800 (PST), firstname.lastname@example.org wrote:
I agree. Intertek Testing Services is supposedly independent. If anyone has
information otherwise, please post.
Very good point.
Here are the original calculations I posted for inspection:
a. Additional cost of more efficient model = $882 - $747 = $135
b. Annual savings of more efficient model = $313 - $288 = $25 per year
c. Payback period = $135 / $25 * 365 / 30 = 65 months (5.4 years)
e. Overall savings = (13 years - 5.4 years) * $25/year = $190
How would we change these to take into account the time value of money?
As always, I'll hazard my math to see if it stands up to scrutiny.
Using the compound interest calculator here ...
that $135 at 5% compounded monthly over the 5.4 years payback period
actually costs $176.75 at the 65-month point.
You're right. That's a big difference! (I don't use credit cards so I won't
factor in the additional, but huge, credit-card costs if paid on
Conversly, the annual savings over that same 65-month period is also
increased, from $25/year to $26.28 per year using the same 5% interest rate
This more accurate payback-period calculation then becomes $177 / $26 * 365
/ 30 = 83 months (6.9 years).
The overall savings now shrinks a whopping 16% from $190 when not taking
into account the time value of money, to (13 years - 6.9 years) * $26/year
Thanks for testing the math. Please let me know what you think of the new,
more realistic calculations which take into account the time value of
PS Can someone in the field write a calculator to do all this math for us?
Vehicle mileage estimates, or for that matter any estimates, are based on a
load of assumptions. Your actual experience will vary according to how
closely your situation matches the assumptions. By the way, vehicle
manufacturers follow a standard test procedure specified by federal law, and
the EPA confirms 10%-15% of the results by conducting its own tests.
I agree that the rated fuel consumption for motor vehicles is off - I
haven't averaged that low for at least 15 years. For instance, my car is
rated 20/29 for city/highway - last week I averaged 33.2 mpg in about 440
miles of mixed driving according to the car's odometer and the reading on
the pump when I gassed up on Friday evening. According the average mileage
display on the dashboard of the car, I got 34.1 mpg, and I suppose the
difference could be due to the attendant (no self service gas in NJ) filling
the tank right up to the gas cap and/or inaccuracies in the pump or
odometer, or even simply to the fact that I fill up the tank at the end of
the day (when the car and the gas is at its warmest) but do about half my
driving in the morning (when the gas is the coolest). Which means simply
that a full measured gallon on a Friday afternoon is probably less than a
gallon on Monday morning simply due to the expansion and contraction that go
with changes in temperature.
The expansion and contraction based on temperature for a volume as small as
a tank of fuel in a car are so tiny that you'd never be able to measure them
with anything around the house, and certainly not the odometer in your car.
The fuel temperature varies over a range of perhaps 60F max, usually much
Just to be devil's advocate, I used to have a Rabbit GTI that I got
with a bad gas cap; the first time I parked it in the sun with a full
tank of gas, the fuel started pouring out around the gas cap and down
the quarter panel :(
the energy guide labels on appliances arent really to determine exact
their real value is in comparing efficenies in a general way.
obviously a home with 8 kids will use a lot more hot water than a
single guy living alone.
with so many variables, incoming water temp, desired water temp,
amount of water used, cost of gas, etc etc,.
everything is a estimate
Well, maybe I'm calculating wrong. There's an approximately 3% difference
between what I calculate as my miles per gallon for last week and what the
car calculated. The coefficient of expansion of gasoline is 0.069% per
Fahrenheit degree. Coincidentally, over a 30 degree temperature difference,
that's between a 2% and a 3% change in volume. For 15 gallons of gas, that
comes somewhere between 3 and 4 ounces of gas.
The meter on the pump reads out several digits to the right of the decimal
point - it appears that this level of accuracy is available at the gas
station. The odometer reads out only to the tenth of a mile, which means
that I don't have the accuracy at my end to calculate this by hand. I don't
know what the internal accuracy is when the car computes average miles per
gallon - I presume the fuel pump knows pretty precisely how much gas it's
pumped, and the odometer measures distance covered by counting revolutions
of something (one of the wheels?), and it seems reasonable that the internal
accuracy of the car's computation is more than adequate to notice a
difference of this magnitude.
I guess the other consideration is that the car is likely computing average
mpg using the gas burned (or at least, pumped to the engine) while any by
hand calculation is basing it on gas bought, and any difference the fill
level will throw the result off. Last week, the attendant took great pains
to fill the tank right up to the brim (he was evidently trying to get the
total to come out to a whole dollar amount), something that usually doesn't
happen. So I have no problem believing that I bought slightly more gas than
Whichever figure is right and whatever the explanation, it still seems to me
that the mileage estimates published by the EPA are too low, and it's seemed
that way ever since I started paying attention (way too many years ago).
According to the EPA's fuel economy guide for 2008, the Prius is rated at
48/45 for city/highway. The 2008 model year isn't very far advanced and
there's only 23 2008 models listed in the shared fuel economy estimates, but
those drivers claim actual mileage of 35 to 56 mpg, with an average of 43.5,
I'd say the estimates aren't that bad. The best driver claims an average of
56.2 mpg for 38% stop and go and 62% highway driving - that car is driven in
Arizona. The worst driver claims a mere 35.1 for a car driven in
California - no percentages for city/highway are given.
Considering that the EPA's National Vehicle and Fuel Emissions Laboratory is
located in Ann Arbor, Michigan, and that Ann Arbor is about 840 feet above
sea level, and that the EPA conducts its own tests at this facility, I think
your claim that the mileage figures are based on sea level conditions is
Considering that starting in 2008 supplementary tests are conducted to
estimate the effects of high speed (up to 80 mph), use of air conditioning,
and cold temperatures (down to 20 degrees F), the claim that current figures
represent ideal conditions also seem somewhat out of sync with the facts.
20 degrees F cold? It is high time that automotive design and testing
accommodate the northern climates where cars last about as long as a snowflake
on a hot radiator. Test in International Falls in February on a track
laden with salt and urea at minus 20 degrees F.
something else - not interested enough to look into it, but I'm
sure they lab test versus "real world."
Think you said you had an Impala, and the 3.1 engine coupled with the
GM lockup trans is an efficient combo. I consistently get 30-31 mpg
highway with mine ('97 Lumina) over a long stretch of varied terrain.
Measured by actual gas pumped into the tank over many thousands of
miles. My '88 Celebrity with the 2.8 did about 28 mpg, but always had
a heavier passenger load.
It all points down to the fact that average Joe citizen can't tell the
difference unless he can find out exactly how they take all these
measurements (The method used and exactly what figures) that each company
used and how (If they did) manipulated those figures to get the result as
they publish. The main thing that the Government is interested in is a
standard across the relevant industry so everyone can make a comparison.
The tests are performed by independent labs to the EPA test procedures
and standards. It's not up to the maufacturers to decide how to
test, nor can they manipulate the results for the cars. Same thing
for the water heaters.
Yes, some of that can certainly be going on. But trying to change
the design of the product slightly to come out better in the standard
EPA test is a lot different than claiming the tests themselves are not
uniform because the manufacturer gets to decide the test method, how
the test is done, etc, and then manipulates the results they publish.
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