"Ed Sirett" wrote in message
...
On Mon, 18 Dec 2006 09:57:42 +0000, Doctor Drivel wrote:

"Ed Sirett" wrote in message
...
On Fri, 15 Dec 2006 22:11:11 +0000, Stuart wrote:

Four of my 7 rads are done in 8mm microbore from a manifold in my hall
and the
other 3 rads are fed by 10mm tee'd in to the 22mm before the manifold .
As I am
getting a replacement condensing combi boiler and the fitter said 10mm
was
preferable to 8 I wondered if cutting the 8mm just after it leaves the
manifold
and then replacing it with 10mm would work better or would the couple
or
three
inches of 8mm still create problems ( if at all) . I had thought all
were done
in 10mm and it was only after he left ( thinking they were all 10mm as
I
was)
that I had a closer look and noticed the difference so lifted a couple
of
boards
over the manifold and checked what was what .

I don't know why it was done that way ...can you not get 10mm manifolds
?


Looking at the other posts it would appear that you have been introduced
to a range of replies.

Provided:
1) The existing system, when it worked, worked well enough to heat all
the radiators enough to heat the house properly.
&
2) There is absolutely no hint of sludge or scale in the existing
circuit

then keeping the existing 8mm and 10mm pipes will be a good choice.

Obviously 8mm pipework is even more prone blockage than larger sizes but
isn't automatically a problem.

The existing system worked on the basis
that the difference between the
flow and return temperatures would be
somewhat more than a system using
larger pipes.

It didn't. It worked on a temp differential of 10C or 11C like any other
system at the time, no matter how big the pipes.

Inasmuch any domestic system is 'designed' rather than estimated (usually
quite well) then microbore systems have a larger difference between flow
and return temperatures than systems using 22& 15mm.

Only if it was not sized right.