On 30-Mar-2004, Mick wrote:

This assumes that the water in the heater is cooling down to ambient
every day.

I never made that assumption, but maybe someone else did.

The only point I made related to ambient temperature is that the energy loss is
directly proportional to the temperature differential between the water and the
ambient air temperature. All of my measurements were made with the water at a
stable temperature (within thermostat limits).