In article , Sam
writes
Hello,

I was browsing through some old posts and they said that 15mm pipe was
suitable for carrying up to 6kW according to one post and 9kW
according to another.

I'm a bit worried! It's very cold upstairs. We moved in last year and
the first thing we did was to insulate the loft. That hasn't been
enough, so I was going to change some radiators to bigger ones.

The thing is that the boiler has 22mm pipe come out of the boiler and
upstairs but on the landing this is reduced to 15mm which tees, with
one 15mm run going to the back rooms and one 15mm run going to the
front rooms. I am sure there must be more than 6kW of radiator
connected to that!

Is this why it's so cold? Will upgrading the rads. have no effect if
it is that the pipe cannot carry that capacity?

I'm not sure if it would be easy to change the pipe work without
ripping up the floor in each room. I would use plastic pipe to weave
through the joists. At the moment they've taken a big chunk out the
top of the joist to fit the two 15mm pipes through. That would be too
small to fit two 22mm pipes in, so I guess I'd be best to drill two
22mm holes in the middle of the joists. How far away from the existing
notch would I need to be to make sure I do not weaken the joist?

I also noticed that the gravity fed HW goes from the boiler in 28mm
pipe but is reduced in the airing cupboard to 22mm.

In both these cases, doesn't it defeat the object of using big pipe if
you then reduce it down later 22 to 15, or 28 to 22?


I'd say your first step is to balance the system, it is quite possible
that this has not been done correctly and radiators closer to the boiler
are stealing flow and therefore heat from the rest. Only if you cannot
achieve a satisfactory balance do you need consider redesign and
modification. The important thing is to go about it in a logical
progressive fashion and not make random changes in the hope of
improvement.

Here's a link for the uk.d-i-y group faq on radiator balancing:
http://www.diyfaq.org.uk/plumbing/rad-balance.html

Other useful; stuff he
http://www.diyfaq.org.uk/contents.html
and he
http://wiki.diyfaq.org.uk/index.php?...ecial:Allpages
but the balancing section there is still a skeleton in draft

In brief, on the subject reducing pipe sizes, thing of the pipework as
the a tree with a main trunk and smaller branches coming off the main,
once the trunk is split there's no need to have a full size branch all
the way to the top just to support a few leaves at the end.
--
fred
Plusnet - I hope you like vanilla