"Geo" wrote in message
...
On Mon, 18 Jan 2016 18:41:40 -0000, "Ian Field"
wrote:


Its square and not cylindrical, and the element is horizontal at the
bottom - that may not accommodate as long an element as diagonal in a
cylinder.

OK - with you now.
Some simulations he-
https://blogs.mentor.com/robinbornof...art-2-warm-up/

There is another threaded bush half way up the tank that I could add a
second element if I wanted to.

useful only if yiou want to keep water hot for handwashing etc without
heating the whole tank.

A well insulated tank costs more to heat up from cold than keep topped up by
the thermostat.

Not as bad heating half a tank from cold, but I'm guessing it would still
cost slightly more.