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?