"Phil Addison" wrote in message
...
On Wed, 13 Aug 2003 00:36:41 +0100, "IMM" wrote:

"Phil Addison" wrote in message
...
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.

It is plain right!

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.

Each rad will not have the same pipe sizes. A small rad may only have
8mm
and a larger rad 12mm. The pipe sizes will create resistance in
themselves.
Manufacturers did not make lockshieldless valves for nothing.

Why on earth fiddle with different
sized pipes to (attempt to) balance
the rads. Just use one size and balance
with the LSV. calculating what
length of what resistance would be
needed to correctly balance is quite
beyond a c/h fitter, wheras turning a LSV is not.

You are supposed to size up the pipe sizes correctly. Sizing up for each
rad on a manifold system is very easy. Attempting to do it on a 22/15mm
small bore system is far more complex.

I bought a new house a few years ago in which the all the rad circuits
were plumbed in 10mm insulated microbore. The lounge radiator was a very
large double, about 2.5 kw IIRC, and at the far end of the lounge
fromthe manifold. It would not get hot enough to warm the room. I checed
the design and found 15mm would be required to feed the load over that
long distance. The plumber, then his boss, all tried to tell me it was
all-right really, because the flow side of the radiators was really hot.
It was only when I got the builder boss in on acold and demonstrtaed
the room was not up to temperature that the reluctantly agreed to change
the microbore feed to 15mm.

But guess what? When I got back from work, I found that because it was
only the return side that was cool they only changed the return feed to
15mm, some 4m in length, and there was hardly any improvement. It took a
long conference with the lot of them to get the feed changed as well.

After that the rad got fully hot and the lounge temperature was fine.

That was because they were plumbers. They obviously didn't have much of a
clue.



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