On 14/02/2020 13:32, The Natural Philosopher wrote:
On 14/02/2020 13:08, simon mitchelmore wrote:
My friend is too scared to turn on the immersion heater during the
day because she is absent minded and only remembers its on a few days
later and so gets big bills.

Not from an immersion heater she wont.

Total heat loss from a decent cylinder is probably less than 50W


But it might be a naked one.