Solution for condensation in a vertical Extractor flue? Spinner Cowl?

[jamesup]

Hi there, grateful for any advice.

Live in a top floor flat where the bathroom extractor is mounted in the ceiling, with a flue pipe extending vertically about 0.75m, topped with a mushroom clowl.

The extractor runs when bathroom lights are on, and on timer after the bathroom lights are turned off. Dripping occurs when it's on and off, notably more so when hot water is being used.

During cold weather, we get water dripping back down the extractor flue, caused by condensation. I've cleaned the cowl and flue and there are no obstructions, but damp air clearly doesn't clear the flue fast enough before moisture condenses.

I've been looking for options for a next step and have considered:

1. upgrading the extractor to something more powerful to push the damp air out quicker
2. insulating the exposed part of the flue above the roof to reduce the condensation
3. changing the cowl to a spinner cowl to create a steady updraft and remove damp air from the flu.

Is using a spinner cowl a valid option here? I've not seen this recommended for a bathroom but would be easy to try so I wanted to check if there was any downside I've missed.

Appreciate any help.

 

[datarebal]

Have you checked the fan is actually extracting? I have seen a fan that was making a noise but actually did not have the fan blades fitted within the fan ..from new.
Hold a sheet of tissue near it to see if it gets pulled towards the fan.

Maybe adjust the timer to a longer duration

An insulated duct might help as might a more powerful fan.

It is become a common problem

 

[jamesup]

Thanks datarebal, yes, done the tissue test, it extracts - but appears to not get the wet air out of the flue before it cools down.

 

[datarebal]

how log does it carry on running after the light is off?

 

[^woody^]

Cowl and fan idea won't work. Insulate the duct and/or fit a condensation trap.

 

[jamesup]

how log does it carry on running after the light is off?

Runs a good long time - drips fall through when it's running if you're using the shower.

 

[jamesup]

Cowl and fan idea won't work. Insulate the duct and/or fit a condensation trap.

That looks like a good solution. Thanks.