On 12/11/2019 10:34, simon mitchelmore wrote:
Condensation is forming inside the 100mm pipe above the bathroom vent
fan which passes through the cold loft (about 10 feet) to a grill at
the apex; the water then drips down through the fan when its off.
This is in a flat hence the bathroom has no outside walls and also I
can't re-route the 100mm pipe horizontally out of the roof.

This is as was fitted from new (1980's) but the first winter for us
hence this must happen every day in cold weather when we take a
shower.

Any suggestions to stop the condensation forming?

Lag the pipe, to save it losing heat so quickly - that should keep more
of the moisture in suspension for longer.

I've even considered fitting some sort of gravity condensate trap
which would have to then have a drain pipe leading out through the
eaves.

Such things are available:

https://www.toolstation.com/extracto...verflow/p73185


--
Cheers,

John.

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