In article ,
"Frank McGuire" writes:
Anybody got any experience of installing / operating this kind of heating.
It's a 2 storey cottage and I'm considering installing 2 circuits (one
upstairs and one downstairs) using a single 15mm pipe in one radiator and
out the next.

That's not quite what a single pipe system is. Start by imagining
a large loop of pipe with no radiators on it. Now you tap them in
to the loop, but without breaking the loop. If you look at it like
an electrical circuit, each radiator would seem to be shorted out
by the loop, but that analogy is wrong as the radiator can be
looked upon as a much thicker pipe which will therefore take the
majority of the flow unless restricted by the valves.

Selection of radiator sizes is much more critical than with a
parallel pipe system. Balancing is then done per loop, not per
radiator. You should take into account the falling average rad
temperature around the loop when sizing radiators.

One of the reasons for this is that the walls are 2.5 feet thick.
It will be fed from an eternal oil fired combi boiler.

I think you might struggle to find plumbers nowadays who understand
single pipe systems, at least in enough detail to design one.

--
Andrew Gabriel