In an earlier contribution to this discussion,
Sam wrote:

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?

It's a bl**dy big rad that will produce 6kW of output. Tell us the size and
construction (single, double, with/without fins) of each of your rads, and
we will calculate the approx output of each.

You then need to calculate the heat losses of each room, and see whether the
radiator capacity is adequate. You also need to calculate the *total* heat
losses, plus an allowance for hot water to see whether the boiler is
adequate.

If the design is ok, it is then simply(!) a matter of making sure that the
system is balanced properly and is not sludged up.

In the rooms which are not warm enough, how hot are the rads getting? [Best
measured with a infra-red thermometer but - failing that - for how long can
you hold your hand on the rad? If you feel the inlet and outlet pipes, is
the outlet a *lot* cooler than the inlet? Are the rads hot all over, or is
there a cooler region in the centre towards the bottom?

How is the boiler stat set? If it's a gravity HW system, is there any
control of HW temperature - other than by adjusting the boiler stat? If not,
chances are that the boiler is set at only about 60 degC - whereas you need
it at 80 to get more heat out of the radiators. [But then, the HW will get
too hot!]
--
Cheers,
Roger
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