On Aug 8, 12:46*pm, Smitty Two wrote:
In article
,





wrote:
On Aug 7, 9:47*am, ransley Mark wrote:
On Aug 6, 8:31*pm, "Jordan" wrote:

I just started thinking about getting an electric water heater timer for
my
3 year old 30 gallon water heater. *I checked some of the reviews for the
Intermatic timers and it looks like everybody loves them and they say
they
practically get their $40 bucks back each month.

Are timers all they seem to be cracked up to be and will turning off the
water heater from 10 PM to 8 AM really save a family of 4 a big chunk of
change each month?

Nobody is getting 40 back, My total bill for the electric tank was
under 40 a month, I know because that is how much it went down when I
switched to Ng. Do a test, my tank still had warm water in it after 5
days when I would leave and turn off the power. See how much it drops
overnight, you will be just reheating it and may save nothing.

Of course it has to be reheated, but once again, that DOES NOT
TRANSLATE INTO SAVING NOTHING. * In fact, the more it has to be
reheated, the MORE he saves.

Sorry, not true.

Exactly what is not true? This is what you stated:

"See how much it drops overnight, you will be just reheating it and
may save nothing.
'

That is what is not true and doesn't make any sense. Of course it has
to be reheated the next morning. The point, once again, is that it
takes less energy to then reheat it in the morning than it does to
maintain it at the normal set temp all night. This is exactly the
same concept and simple physics as turning back a thermostat overnight
on a home heating system. Are you going to tell us that doesn't save
energy too?

And again, let me state the disclaimer, I'm not saying he's going to
save a lot of energy. I'm not saying it's worth it to install a
timer. Maybe it is, maybe it isn't depending on exactly how much
energy he can save. But that is a totally different argument than
saying turning off the water heater doesn't save any energy because it
has to be reheated.

It's the change in *rate* of heat loss that determines
the savings. The rate slows, slightly, as the temperature difference
between the water in the tank and the surrounding air decreases. But
that difference is essentially negligible.

IOW, looking at a loss of 20 degrees in 10 hours overnight: if it loses
10 degrees in the first five hours and another 10 in the second five
hours, there is absolutely *zero* savings.


Let's look at the previous example you gave he

Let's say your HW is at 130 degrees, and it cools to 110 overnight in
the tank with the heater off. Do you *really* think that the slope of
temp over time isn't close enough to linear to disregard its
shallowing
in this *real world* consideration?


The rate of heat loss is proportional to the temp difference. Let's
assume it's in a basement at 60 degrees. At 130 degrees, the temp
differential is 130-60, or 70 degrees. At 110, it's 110-60 or 50
degrees. So the temperature differential has gone from 70 to 50, or
about a 30% difference at the end of the period. It's a decaying
exponential so more of that 30% benefit occurs in the earlier period
than in the later. But even if you assumed it was linear and went
from 0 decrease to 30% at the end of the period, the tank would have
an average of about 15% less heat loss over say 6 hours. That isn't
zero and it's not negligible either. Again, whether it makes it
worthwhile to install a timer is a completely different discussion.



However, if it loses 10.1
degrees in the first five hours and 9.9 degrees in the second five
hours, then you'll save by turning it off overnight. How much? Maybe a
penny. Likely not even that.



Clearly that can't happen. because the rate of heat loss is
proportional to the temp difference and it's a natural log decaying
function, which according to physics and math isn't close to being
linear. In other words, it's going to lose much less in the second
five hours.