Andrew Gabriel wrote:
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

I thought the reason the radiators heat up is gravity feed, i.e. the
cold water 'falls' into the pipe after the radiator and 'rises' into it
at the beginning by virtue of the differing density. This would fit in
with my experience (I have a one pipe system which I'm planning to be
rid of) where the pipework all gets hot well before the radiators do.
It's not a great system as Andrew said as there is a temp drop around
the circuit.

To be honest there's not much more work involved in making a hole big
enough for a pair of pipes compared to a single (again I have some
experience as my walls are 2' thick so you're only ahead by 6"). It
will then be easier to balance, more efficient/effective and any
plumber who comes in subsequently will be able to work out what to do.
I had real problems with mine when I had to change some rads due to
them rusting through, ended up having to sort it myself.

Incidentally could you point us all in the direction of your boiler
supplier, I would rather nbot have oil but the idea of having an
"eternal boiler" strikes me as a good one!

Fash