On 1-Apr-2004, (Chris Lewis) wrote:

Not quite. Scale does not "circulate".

Thermal regulation will suffer, recovery time will suffer (possibly
extremely),
more heat will be lost out of the tank due to overswings/higher delta-Ts,
insulative effects etc.

I would be really surprised if that has more than a 10% effect on heat loss
through the tank shell.

It's easy to contrive examples of where timers/demand heaters/etc will either
save you lots, save you insigificant amounts, or actually cost you more
money.

There are LOTS of factors involved - duty cycles, temperature settings, usage
patterns, age, tank insulation quality, pipe insulation/size, tank size,
energy
costs etc.

Whether any specific measure will be worth the effort depends a lot more on
your unique circumstances than the technology per-se.

I agree that there are lots of factors that offer potential savings. But my
figures were made with no additional insulation and no timer or other potential
energy saving device. So I believe the heat loss cost I measured is an upper
limit on how much can be saved by adding insulation, timers or any other type
of device. A perfect tank would have 0 (zero) energy loss through the shell.
That tank will cost $4/month less to operate. You can't do better than that.

Another person posted some industry data showing that an electric tankless
heater saves $2.30/month. That's almost exactly what you would expect from the
measurements I made -- the tankless heater saves about half of the heat loss.