Bathroom extractor fan venting

[richards1978]

Hi all,

Short-version:
Can anyone recommend a vent to use for properly terminating a 4" extractor fan hose into a soffit board, and how to stop the vented air re-entering the loft via the existing linear vents?

Long-version:
After the in-line fan failed on our bathroom extractor fan, I went up to the loft to take a look at it. The fan looks like an easy swap, but I also noticed the end of the 4" vent hose was basically just lying open on top of the soffit board in the eaves of the loft - guessing whoever fitted it thought it would just vent through the linear soffit vents around the edge of the roof.

No idea how long this setup has been in place, but whoever did it clearly didn't understand physics, as the vented damp air had just risen upward into the loft area making it damp and causing mould to form on the roof lining and rafters around the end of the hose - fortunately it hasn't caused any serious damage/rot... yet.

Is there a proper way of terminating these hoses into the soffit, and a vent anyone would recommend to do this?

I've seen a few various circular soffit vents (which are basically just holes with a louvred cover) but these seem more for ventilating the loft rather than an vent for an extractor fan, and my worry is that the hot damp air will just rise straight back up into the loft through the linear soffit vents.

Thanks
Rich

 

[Ivor Windybottom]

You can't. It's a very common problem but you're right to be concerned - the warm humid air will be going straight up into the loft and condensing there, potentially rotting timbers.

The best way is to go up, out of the roof. I've fitted a vent tile on our current home, it works great. I did it all DIY. It took a bit of creativity to seal the 4" vent pipe onto the 110mm soil pipe it was designed for (they're not the same size), but it worked...

https://www.diy.com/departments/manthorpe-granulated-sand-red-plain-tile-vent/5061116421030_BQ.prd

The fan is ceiling mounted - most fans have this option but check before ordering. It's a lot easier to cut a hole through a ceiling than a wall, the big advantage is that it's then in the middle of the room rather than an edge or corner.

Don't use flexible hose, it massively reduces the flow due to the bumpy edges and is also prone to puncturing, by the mice and rats that many houses have but the owners don't know about.

This was a toilet. For the bathroom I'm going to look at higher flow options - possibly something more like a chimney that protrudes out of the roof. But the tile vent seems adequate.

 

[richards1978]

I think you've confirmed what I was afraid of.
Fitting a roof tile vent isn't what I really wanted to do, but it looks like that is only way.

It looks fairly easy on YouTube, once you're on the roof. It's the getting oj the roof part I' worried about.

 

[mikehammer69]

You don't necessarily have to vent through the roof

 

[Murdochcat]

One of these

4 Inch (100mm) Fixed Wall Grille - White | Manrose (1152W / MONV244W)

 

[JohnD]

Is there a gable wall?

 

[richards1978]

Unfortunately not; it's a hip roof.

At the bathroom floor level, the bathroom backs onto a small loft in the garage roof along the main external wall, and the other external wall is mostly window, so it's not even possible to get a wall vent fitted inside the bathroom itself.

 

[JohnD]

If you're concerned about steam blowing back up the eaves, I suppose you could extend the pipe a bit and put an elbow on it so it blows outwards. Boiler flues sometimes have a sort of periscope end. Have you got a good powerful ducted fan?

My boiler and cooker hood are near a corner so the wind swirls round it.