On Mon, 15 Oct 2007 14:41:58 +0100 someone who may be Peter Parry
wrote this:-

The other possibility is that the original poster thought that a
second hot water cylinder was necessary, to pre-heat water going
into the main cylinder. Such an approach was advised in the past as
a way of avoiding replacing the main cylinder.

It is still advised as a method of getting the most from an active
solar system.

"neither [flat panel nor evacuated tube] system can be guaranteed to
continue to give the maximum possible output once more intrusive
auxiliary heating schedules are introduced.

If the "intrusive auxiliary heating system" is controlled separately
from the solar system. However, if they are controlled together, by
the same controller or controllers which speak to each other, then
any such problem does not arise.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54