I agree that the energy used does not depend on the voltage. However,
it will change the calculation
of the energy used. The parameters that were used in the calculations
were measured except for
voltage.

As you say, the voltage will change the duty cycle of the heater,
keeping the energy use relatively
constant (neglecting line losses). Thus low voltages will lead to high
duty cycles (and vice versa),
so the particular duty cycle measured is associated with a particular
line voltage. That line voltage
was presumed, not measured.

Phil Sherrod wrote:

On 29-Mar-2004, Edward Cheung wrote:



Nice work on the investigation. My minor comment is that you used a
standard line voltage in your
calculations. How important is this? Probably not much. In my case, I
just checked the voltage change
over one day. It peaked at 123.4V, and the min was 118.6V. If one
assumed 120V, there would be
only about 2% error



The line voltage will make no difference in the total energy usage, it just
changes the duty cycle.