The reason I want to do this is because I have an existing pipe which
is routed from my apartment to the roof. I now need to get three pipes
up there to support the new combi boiler intake and outlet plus the
bathroom extractor.

I am imagining a form of pipe of the same cylindrical pattern as the
pre-existing pipe but with a Y-section form through the length of it
so that it has three separate sections. i.e. so that a cross section
would look like a pie chart of three pieces.

The reason I want this is for a bathroom and boiler installation where
this pipe contains the intake/outlet and bathroom fan extractor. The
boiler only needs 5cm plastic pipe (19cm2 area). 1/3 of my 10cm pipe
(total 78cm2 xsection) is suitable for the boiler. The bathroom fan
may need a bit more power to force the air through the smaller section
though.

"Jo" wrote in message
...
The reason I want to do this is because I have an existing pipe which
is routed from my apartment to the roof. I now need to get three pipes
up there to support the new combi boiler intake and outlet plus the
bathroom extractor.

I am imagining a form of pipe of the same cylindrical pattern as the
pre-existing pipe but with a Y-section form through the length of it
so that it has three separate sections. i.e. so that a cross section
would look like a pie chart of three pieces.

The reason I want this is for a bathroom and boiler installation where
this pipe contains the intake/outlet and bathroom fan extractor. The
boiler only needs 5cm plastic pipe (19cm2 area). 1/3 of my 10cm pipe
(total 78cm2 xsection) is suitable for the boiler. The bathroom fan
may need a bit more power to force the air through the smaller section
though.



How about three square section ducts. Ducting doesn't have to be circular,
it only needs to be of a certain internal cross sectional area no matter
what shape it is.