Replacement bathroom extractor fan

[JohnW2]

If fans are so brilliant at removing 'condensation' from a room then why do they not remove it from a duct?

The idea is presumably that they 'prevent', rather than 'remove', condensation - by removing air containing a lot of water vapour before that water vapour condenses on cool surfaces.

Once condensation has happened (i.e. water vapour has turned into liquid water on walls etc.), there's not all that much that a fan can do to remove it, other than (perhaps) replacing air in the room with air of lower humidity, thereby encouraging evaporation - but such evaporation is a pretty/very slow process.

From the description in the OP it appears that the top of the duct is not preventing entry of water and dirt from outside.

Yes, maybe - and, if so, that's a more fundamental problem than any 'condensation'.

Kind Regards, John

 

[conny]

Where the vent exits the roof, (i.e. outside), does it vent straight up to the atmosphere? If it does then it should have a conical cap fitted, which has the lower edge below the top edge of the vent pipe. A bit like a Chinese coolie hat, that comes down over the edge of the vent to prevent condensation running back down and rain being blown in. Fitted an S bend trap to collect condensation is asking for trouble because the fan would not be able to blow air through the water trapped in it.

 

[Norfolk Broad]

It was not successful in a kitchen or bathroom

Thanks, John

I wondered as much, and is probably a stretch too far for this application.
They don't strike me as having the same sort of air-shifting properties as a dedicated fan, so will give this a miss for now, thanks.

 

[Norfolk Broad]

...I would have thought that condensation could/would arise (to at least some extent) in the horizontal run of duct between fan and the 90° bend. If that happened, that run of duct could presumably 'fill up with water' with the condensation trap fitted where indicated in your diagram?

Kind Regards, John

Hi John

I see what you mean. That was why I was considering an S-bend at the bottom of the vertical flue to trap water and debris.
I would make a point of clearing it out every six months (hence the litter tray).
But an S-bend may restrict the flow too much, so perhaps I'll try and put a slight "fall" in the horizontal section, so that any water will settle under the vertical section and, eventually, evaporate.

 

[Norfolk Broad]

Yes, backdraft flap in/ near the fan.
Have a read of thd product information. Looks like they sell an internal one. Not sure if “internal” means “not outdoors”, or internal to the fan…

That's great, thanks.

I figured the thrust from the fan would be better immediately after the fan, and hopefully allow the shutter to open wider.

 

[Norfolk Broad]

Where the vent exits the roof, (i.e. outside), does it vent straight up to the atmosphere? If it does then it should have a conical cap fitted, which has the lower edge below the top edge of the vent pipe. A bit like a Chinese coolie hat, that comes down over the edge of the vent to prevent condensation running back down and rain being blown in. Fitted an S bend trap to collect condensation is asking for trouble because the fan would not be able to blow air through the water trapped in it.

Yes, there is a more fundamental problem with the capping on the vertical flue, which I'm not prepared to address just yet!

The existing fan is woefully inadequate and in the wrong location, and has no condensation trap. I think most of the moisture is running down the inside of the vertical flue, and not coming straight down with the rain, so hoefully the condensation trap will deal with most of that.

I will need to speak to the landlord/freeholder of the block of flats about replacing the cap on the roof. That might need to be combined with another repair, as I'm sure he will charge of scaffolding etc.

For now, I just need to mitigate the immediate problem above my shower room!

 

[JohnW2]

Hi John

I see what you mean. That was why I was considering an S-bend at the bottom of the vertical flue to trap water and debris. .... I would make a point of clearing it out every six months (hence the litter tray). But an S-bend may restrict the flow too much ....

Quite so. Indeed, as has been said,if that S-bend were to fill with water, it might actually completely prevent any air flow! I personally would not contemplate that approach.

, so perhaps I'll try and put a slight "fall" in the horizontal section, so that any water will settle under the vertical section and, eventually, evaporate.

That would presumably work, provided that there was not too much water. Best would be to have a 'fall', coupled with some way of 'letting the water out' at the end of that fall (i.e. the bottom of the vertical run. I would have thought that one could probably devise some way of doing that.

kind Regards, john

 

[Norfolk Broad]

That would presumably work, provided that there was not too much water. Best would be to have a 'fall', coupled with some way of 'letting the water out' at the end of that fall (i.e. the bottom of the vertical run.

Thanks again, everyone.

Just to be clear, the current situation with water drips isn't persistent, nor a huge amount. It's more of a minor nuisance that happens occasionally.

Just to clarify, the vent in the roof is actually mounted on the ridge tile, so definitely the responsibility of the landlord:

I think it will need to be a much bigger problem before I approach the landlord about this.

In the meantime, hopefully relocating the inlet vent above the shower, and using a more powerful fan, will force the steam up the pipe.

Thanks again
NB

 

[JohnW2]

In the meantime, hopefully relocating the inlet vent above the shower, and using a more powerful fan, will force the steam up the pipe.

That's probably true - but bear in mind that the more steam you manage to 'force up the pipe', the more condensation is likely to occur within the pipe (including the 'horizontal' portion)

Kind Regards, John

 

[messmerize]

Hello Norfolk Broad - can I ask which fan you ended up installing, and if you are happy with it now that it's a few months on? We are looking to replace our axial fan with an in-line fan and have been considering the Tornado Turbo Tube that you mentioned. Thanks so much.