Re: Power cost of idle electric water heater

 

between

Right.  So you're not measuring the cost of the water temperature rise.

 

For the same temperature differential, a larger tank has more surface area
than a smaller tank, and will therefore lose more BTU's per hour than will
the smaller tank.

The larger the tank, the fewer BTU's lost per unit volume in a given period
of time, but the absolute amount of heat lost varies with the radiating
surface.

It is not the case, as originally stated, that larger tanks have a smaller
surface area.  It is true that larger tanks have a smaller surface area per
unit volume.  The orignal statement, as posted, was incomplete and therefore
incorrect.

 

That sounds somewhat askew - what you've just said is that the electric rate
was _never_ the normal rate.  You seem to be telling us that if, for
example, the normal rate was ten cents per kilowatt-hour, participants in
this time of day pricing scheme could buy electricity for either five cents
or for twenty cents a kilowatt-hour, but never for ten cents.

Is that right?

 Lou wrote:

Yes, that is correct.  I just checked my utility co. web site
<HTTP://www.xcelenergy.com> and here are their rates.

Normal residential service - 7.092 cents per kWh
Time of day rates peak     - 13.633 cents per kWh
Time of day rates off peak - 3.163 cents per kWh

The time of day service is an optional service, if you do not sign up
for it you will be charged the normal residential rates.  If you can
move enough of your electric usuage to the off peak time you can save
money.

This is what my electric co. offers, other companies may have different
plans.

Mark

 


It is true that the volume increases faster than the surface area.  So what?

Once you have a tank large enough to supply your hot water needs, any increase
in volume beyond that point will require an increase in surface area and more
heat loss.  For maximum efficiency, you should use the largest single tank that
will supply your hot water needs.