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Smitty Two

In article
,
wrote:

On Aug 8, 11:42*pm, Smitty Two wrote:
In article ,
(Doug Miller) wrote:

In article , Smitty
Two
wrote:

Here is the difference to which I refer: You save money on the home
heating issue because you're lowering your average home temperature. You
don't save money (of any appreciable amount) on the hot water tank,
because you aren't lowering your hot water temperature. All you're doing
is making up the heat loss in one big chunk in the morning, instead of
incrementally throughout the night.

I disagree. By shutting off the water heater at night you are also
lowering
the average temperature of the water -- and the situations are the same.

Sure. But you "use" the air in the house a little differently than you
"use" the water in the tqnk. You aren't lowering the average temperature
of the water that you use, at all. That's the difference.

Talking about "using" the air in the house is a complete distraction
and has nothing to do with the heat loss principle at work here.

But it *is* relevant. The fact that you don't see the relevance makes me
think there's a significant piece of the puzzle to which you've turned a
stubbornly blind eye.

I
could have two water heaters, one uninsulated, the other insulated.
Both of them are filled with water and have the water inlet valves
turned off. Hence there is zero water "used" in either case. Are
you going to tell us that one tank doesn't consume more energy than
the other? Or how about we set one tank to 110 and the other to
140? The 140 tank is going to use more energy than the 110, even with
zero water "use".

I agree that the uninsulated tank uses more energy. I agree that the
tank with the higher setting uses more energy. In fact, the way to save
on your HW costs is to lower the setting. That is the equivalent to
lowering your thermostat at your house.

And also, while it doesn't matter, you are lowering the average
temperature of some of the water you use with a timer. Typically
you'd set the timer to turn the water heater off some time before you
go to bed, because the tank will still be full of hot water for any
use in the last hour or two and the longer it's turned off, the
greater the savings. After the timer turns it off, if you then draw
enough water, which likely would occur occasionally, you are in fact
using water at less than normal temp. Or if someone happens to wake
up at 3AM and draws hot water, it's at a lower than normal temp.

*Exactly.* I agree 100%. And that's the *only* significant reason why
turning off the heater at night might help, because it forces you to use
less hot water, and forces you to use hot water that is at a lower temp,
assuming your scenarios take place, which they likely do. Wouldn't it
make more sense to just lower the setting 24/7, if saving money is the
objective?

But the bottom line is, this discussion about air being "used" has
nothing to do with the physics of the water heater or the house
situation. The energy savings are a function of the fact that heat
loss is proportional to the temp difference between whatever is hot
and being heated and the temp of the surroundings. The lower the
temp difference, the lower the rate of heat loss.

And as I said in response to Doug, it's likely that turning off the WH
heater at night to reduce the rate of heat loss might save enough to
power the timer. He thinks so, by a few pennies. I don't.