On Aug 17, 10:32*am, Graham Jones wrote:
Hello,

What are the consequences of 22mm CH pipe going into 15mm and back
again to 22mm before yet again going to 15mm for final run to
radiators?

House currently has 22mm from boiler which runs under landing and
under hall, from this is 15mm to rads.

As part of extension work we are having a new boiler which will be in
a new location. Plumbers have 22mm from boiler which runs for about
about 3m, then down into 15mm for new rads. But it looks as though
they will then take this 15mm and connect it to existing pipework
(22mm).

I estimate that the length of 15mm pipework between the two 22mm runs
will be about 2m.

Is this OK?

How many rads will flow through the 15mm pipework. At each place
where the pipework branches there is the possibility to use smaller
pipes. A a general rule of thumb (amateur) I ran 22mm from the boiler
to the branch point where there were 3 or fewer radiators on the
branch. Then I dropped to 15mm Individual rads got 10mm pipe.

In fact, in my case (ordinary victorian end terrace) the size limit
was becuase of the flow noise rather than thepressure drop. if the
water velocity is too fast you hear the sound of it in the pipes and I
wanted to avoid that.

Robert