On Mon, 19 Jan 2004 05:34:49 -0500, someone wrote:


.... They are much more efficient. rest cut
..... Basicly you will just heat the water to be used,

The heating phase of an electric (tank) heater is pretty close to 100%
efficient. You are not going to beat the efficiency of that phase
with a tankless. Both kinds heat the water which is to be used. The
tank, you use water that is already hot, it was heated first and then
stored ready to go, no further heating required. The tankless needs a
huge btu capacity to suddenly heat up cold water on demand. Same btu
to heat cold to hot, just doing it over a longer period with a
(relatively) small element vs. all at once with a larger one.

(If the local utility charges a "demand charge" there goes your
savings, also for the same useage you generally need more electrical
capacity for tankless since you don't have a long period to slowly
heat water to be stored; you need to heat it all at once, so there are
initial wiring implications.)

Now, yes, since the storage is not 100% perfect and has some standing
loss, you do pay for that. But you do NOT actually heat *any* more
water "to be used". The water in the tank that has been heated gets
used. You do not have to heat any "extra" water with a tank, while it
is service. (Pedantically, I suppose you could say that when the tank
is taken out of service, there is one last tanklfull that was heated
but not used, out of the tens of thousands of gallons hot water used
over the years.)

Anyways, I actually think we kinda agree, in a direct replacement
situation what little savings is the storage loss. If you designed
the house differently with multiple units you could also reduce piping
loss.

But then you could reduce piping losses with multiple tanks too! Most
American home can find the space for a tank more easily than in
European (or Japanese) homes, so space saving is probably NOT the
reason most Americans are thinking of these.

Bottom line, I doubt most Americans could justify these for a
retrofit, on a "saves money" basis. TANSTAAFL.

-v.