"David Hansen" wrote in message
...
On Fri, 07 Nov 2008 18:03:20 GMT someone who may be "The Medway
Handyman" wrote this:-

AIUI the 24"/27" does the heavy lifting & the 11" is just a top up. The
11"
one won't heat enough water fast enough for most domestic applications.

Other than a bath, and perhaps a power shower, a short immersion
heater is fine for normal domestic use. It will heat up the top of
the cylinder rapidly enough to cope with demand.

Those who want deep baths, or are heating water overnight for
storage in a properly insulated cylinder, will consider a longer
heater.

If one wants both the whole cylinder and the top part to be heated
in different circumstances extra bosses can be fitted. I also have a
vague recollection of dual element immersion heaters which fit in
one boss, though I have never encountered one that I can remember.

David Hansen, Edinburgh


There are still RedHeat Dual elements on sale. They have a long and short
element. The long one used to heat the whole tank on the over night tariff
and a small one for boost during the day. But they are usually fitted on
cylinders that have 4 inches of soft insulation around them. It is the only
way to make them economical enough to use.