On Tue, 12 Aug 2003 23:51:40 +0100, "IMM" wrote:

Just to add:

Plumbing Mechanical Service Book 2, a NVQ plumbing book. This is not a DIY
book so please don't buy. It has a section on heating, and a sub section on
Mini-bore on page 170. It says:

"If the manifolds can be situated in such a way that the branch flow and
return to each radiator is approximately the same length, the frictional
resistance will also be approx the same, making the system self balancing".

That is plain wrong. Making all the pipes the same length will indeed
make the each rad feed have the same resistance. But that is NOT what is
required. Different sized rads require different flow rates otherwise
the small rads will steal flow that is needed by the large ones.
Balancing is the process that adds the extra resistance to the small
rads to achieve this.

It is not at all unusual for so called professional authors to get these
things totally wrong. Hopefully, it is only the writer of that book that
is ignorant rather than the institute he wrote it for. I recommend that
students of NVQ do not buy it either.

And on page 171:

"In a well-designed system balancing should not be necessary as the aim is
to keep all pipe runs to heat emitters at, or near, as possible, the same
lengths."

Same error carried over. very bad show. Plus in the vast majority of
installations there is now way the runs can all be the same length.
Unless the architect bases the whole property design on achieving
equidistanced and equisized radiators. Can't see it getting on Grand
Designs though.

And on page 172, there is a cut-away of a twin entry rad valve without
lockshield adjustment because in properly designed mini-bore systems, which
is easy to do, balancing is not required.

Sigh....

--
Phil Addison
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
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