Extractor fan - is this normal on outside wall

[James South]

Hi,

We had a fan installed a year ago in our bathroom and noticed over the last few days, as it has got colder, that these kinds of marks are appearing on the outside wall. I'm assuming this is just the air condensing and running down the wall. Is this a problem apart from aesthetics? There is no water running down the inside of the loft, no any sign than the ducting is damaged. The fan is a Vent-Axia VASF100T.

There does appear to be a little condensation in the loft, but it's on the other side of the roof and only in one or two spots, not the whole side of the roof.

Thanks

Jim.

 

[EFLImpudence]

Need better picture.

 

[James South]

Need better picture.

Sorry, really hard to get a good picture as it's so high up. Using a torch and phone camera.

 

[Taylortwocities]

Well, warm air in a cold duct will condense. It has to go somewhere. At least the duct is slanted so the condensation runs to the outside!

 

[JohnD]

you can flop loft insulation over the duct, so it loses less heat and will get less condensation.

if you turn on the fan before the taps, it will then warm up the duct before the steam arrives.

 

[James South]

Thanks. Yes the fan is connected to the light so starts up as you enter. It also has a 10-20 minute run after it's turned off. We have some loft insulation over part of the ducting before it rises to the outlet. The 'run' is very minimal, maybe a meter at best as the fan is next to the wall.

 

[RF Lighting]

It’s better that the condensation runs outside rather than back in to the fan

 

[SimonH2]

You can get traps designed to collect the condensation in ducting and send it down the drain - if the condensation is an issue, and there's convenient access to a drain, then you could fit one of these just inside the wall.

 

[James South]

I'm not sure there is easy access to a drain. I'm also not the most confident in the loft. There is no water coming back in via the fan and no damp patches on the ceiling near it so I think it's ok at the moment. I've been in the loft while it's working and cannot see any steam rising from it etc so assuming there isn't much/any escape of moisture etc.

 

[SimonH2]

If the duct is intact you won't see any vapour. One thing to look out for though is that water will pool in the duct and find any gaps/holes/unsealed joints - from where it will drip slowly onto your ceiling. If it's rigid ducting then all the joint will need to have been well sealed. If it's flexible then that applies, but there's also the risk that it's had damage to it during handling - it's typically only lightweight plastic with a wire support coil in it. If the drips are light enough, it'll just evaporate away and you won't see a damp patch .... until .... the long term dampness has degraded the plasterboard and you find there's a patch with no strength left.