External hole for extractor fan and materials

[olly330]

Electrician is fitting an extractor fan to bathroom ceiling but as he doesn't know much about the actual exit hole for the extractor so I have asked a brickie to drill the hole at the gable end of the house, its a cavity wall so the hole will be quite deep

The electrician will install the extractor fan in the bathroom ceiling, above the bathroom ceiling is the loft where i presume he is going to run ducting to the point where the new hole is drilled to exit the gable end.

The brickie has asked me to double check materials.

The hole will be drilled approx the red dot in the pic:

Please check I am getting the correct materials for the brickie:

100mm wall outlet flap which will be fitted to the hole on the outside

4" extractor fan ducting

The only thing I am unsure of is once the hole is drilled, it will be going through a cavity wall so its quite a deep hole. The outlet flap only has a small plastic profile on the back that i think will get pushed into the hole and siliconed, but I dont think this will be big enough to go through the cavity wall and come out into the loft so the ducting can be connected to it.

Is there some sort of peice to be used to make the wall outlet actuall have something for the jubilee clip to connect to inside of the loft, how else does the ducting from inside of the loft stay in place to vent out of the hole?

Thanks

 

[olly330]

Just seen this on toolstation, is this the missing piece that will be pushed trough the cavity wall hole, vent push onto one end and ducting to the other?


100 Round Pipe 100mm x 350mm

Description
Fits over components with 100mm o.d. round spigots. Ideal for installation within a cavity wall. Round internal connection is 100mm i.d.

 

[Iggifer]

You can use the solid pipe in place of flexi ducting entirely if a) it's long enough and b) the hole is drilled straight.

You can also not bother with the solid pipe, and use flexi all the way, as it's a 4" hole through the wall, plenty of room to get your arm in and pull the duct through.

Option 3, and the one often used as it works out cheaper if you're doing more than one fan, is to just use a bit of 4" soil pipe and cut to size.

Solid pipe is better than flexi ducting as it creates less turbulence and therefore better airflow. Sounds like your electrician will need to at least use some flexi if it's a ceiling/in line fan going out of the wall

 

[EFLImpudence]

Yes that's the stuff.

The flexible ducting should rise quickly from the ceiling and then run downhill to the wall so the outside hole should be as low as possible.
It can be suspended from the rafters or rest on a wooden platform (planks) or you could use rigid pipe for the whole downhill length.

It would be wise to insulate the ducting.

If you haven't bought the fan yet an in-line fan in the loft is a better solution.
https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=inline+extractor+fans

 

[stillp]

I suggest you get a shroud for the outlet, to reduce the amount of rain blowing in.

 

[olly330]

thanks for all the replies, really helpful.

i hope this image is the correct way of doing it:

so the ducting/solid pipe has to rise above the vent hole and then fall back down? I drew this into the image. Hence its best to try and keep the vent hole as low as possible so that the ducting can easily rise above it?

Also, as solid pipe is better how do you deal with bends, as in my scenario the solid pipe would go straight up from the extractor fan, the need to turn left, then down, then left again to join into the vent hole. Is there some way of adapting it or joining it?

Thanks for the suggestion of an inline fan, i will ask the electrician to use one of these as i agree my current bathroom has one of these and its tons better than the usual ones.

I think this is the type of shroud thats required?:

So would the wall outlet flap thing go first and this fit over it, or is this all that's needed over the hole?

Thanks again

 

[stillp]

So would the wall outlet flap thing go first and this fit over it, or is this all that's needed over the hole?

The flappy thing will help stop backdrafts, but it'll probably make an annoying clatter in the wind.

 

[EFLImpudence]

I know it was only a quick sketch, but would be better like this:

 

[olly330]

Thanks EFL, that's brilliant, really appreciate you taking the time to do that,makes is much clearer.


In regards to the cowl or flappy vent, can the cowl be fitted over the flappy vent, or it is better to to just have the hole and then the cowl over the hole (no flappy vent)

Thanks

 

[stillp]

In regards to the cowl or flappy vent, can the cowl be fitted over the flappy vent, or it is better to to just have the hole and then the cowl over the hole (no flappy vent)

Try with both fitted. If the flap is noisy remove it or fix it open.

 

[olly330]

I won't have ladders to get that high once the roofer has gone so I think I'll get the cowl vent cover instead of the flappy one unless there is any problem with this?

 

[JohnD]

Cowl vent much better. I use them and they withstand coastal storms. They rattle less and unlike the flappy ones I have never had flaps break off and blow away. Even if it did, the cowl would still keep rain out.

My cowl vents look like your illustration and have a single flap inside.

 

[Hyper88]

I am not a fan of flexi ducting. I also think longer runs decrease the efficiency of the fan. I have a extractor fan directly on the wall and I don't think it is powerful enough.

Have a look look the following :
http://www.envirovent.com/home-ventilation/products/bathroom-extract-fans/

I like their heatSava product. It is like opening the window without loosing the heat.

(There was another company, but I can't remember the company, but they had one to draw fresh air in, whilst extracting the damp air). The problem with most extractors is that you need to have them running for a long time, to let all the condensate out.... however, most fans over runs only work for 20minutes.....

I have never bought their products, but have seen them an exhibition.

I also have the brown flap and it keeps flapping when we have high winds.

 

[olly330]

How do you create a bend with the plastic ducting?

The extractor fan will come up into the celing and plastic ducting connected to create the rise, but then need to go 90deg left towards the gable end.

Are there adapter/elbow pieces available to create the turns?

Also, can the joins just be taped together using duct tape?

 

[SFK]

Try a google search for "100mm duct 90 degree" and one of the suggestions is :

https://www.tlc-direct.co.uk/Produc...CUT418y8OBp3BCZaAUNa-DpRzamFt8yh6gaAlpR8P8HAQ