In article , Sam
writes
On Sat, 12 Jan 2008 11:20:40 GMT, fred wrote:

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.

Thanks. I could understand that but the reduction is size occurs
before the branches. The 28mm goes from the boiler to the airing
cupboard but before it gets to the cylinder changes to 22mm; there are
no branches on that it runs to the cylinder only. The CH goes from the
boiler in 22mm to the landing and splits into 15mm before that
branches. My other worry is that once it's branches, posts here said
15mm supports only 6kW. Surely one big rad could use all that up?

Do you mean a single 22 reduces to a single 15, I ask as you say splits
into 15mm which suggests 22 splitting into 2 (or more) 15mm.

28mm dropping to 22mm for a short length is ok as (say) 8m of 28mm plus
2m of 22mm has less resistance to flow that 10m of 22mm.

The reduction to 15mm before the branches doesn't sound right but it may
still be a serviceable design, try the balance and if that doesn't sort
the problem then an upgrade to 22mm may be in order for a further part
of the run.

Gravity fed H/W is not my forte but the heating comments should still be
valid, I assume there is a separate pump and zone valve for the heating
circuit.
--
fred
Plusnet - I hope you like vanilla