Condensation problem in bathroom vent fan tube

[simon mitchelmore]

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?

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.

The vent fan comes on when the lights come on so every visit gets the vent fan being used.

[John Rumm]

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

Such things are available:

[Tricky Dicky]

One possible solution is to use insulated ducting:

I believe it is mandatory on new installations under part L. The above company are quite good for having a comprehensive stock of various ducting and their helpline is particularly good at helping you get the right stuff, the bloke I spoke to was very good even though I was only spending approx. £60 with them. Alternatively if your duct is running along the top of the joists just feed your existing insulation over the top of it. I am not sure if it will entirely solve the condensation issue but will surely limit it.

Richard

[simon mitchelmore]

Thanks guys, really helpful, obviously its more a common than I thought.

[Tricky Dicky]

The example above was just the first one that came up did not notice it was 400mm but the more standard domestic types are available from the same supplier.

Richard

[The Natural Philosopher]

I got this not in extractor fan ducting but in foul stack venting. The pipe ran horizontal and exited under the eaves high up.

It sagged, watre bollected at a low point and te joint wasnt very hood...and water ended up dripping down a wall below.

All my vents now slope down towards the outside

[David]

Consider fitting a humidistat?

It may be that you are not clearing out all the humidity if the fan is linked to the light switch.

In theory after a while the warm air should clear all the humidity out. Granted that when it cools down there could still be some condensation but this might reduce it enough to stop the dripping.

Cheers

Dave R

[ARW]

NHBC require it when in a loft (as did the 1980's Dr Who props department to make aliens)

The 4" stuff (as you later pointed out) is a bit cheaper-;)