Bathroom Extrator Fan Ducting

[hoyboy]

I need to install an extrator fan and ducting in my flat. However, to get the ducting outside is very difficult - I need to go through about 4 x 90 degree bends over a small space (about 1-1.5m). Are all the bends going to cause problems? Does it just mean i need a more powerful fan? Is there any rule of thumb to show how much stronger?

Otherwise, is condensation the only main problem and so long as all ducts are angled downwards this should be OK?

 

[Richard C]

Not ideal but as long as the total length is less than 3m & the fan you use is designed for extended ducting you should be OK. Not all fans are designed for this so make sure you check the fan spec. & ensure the ducting always goes downhill with no sagging bits that can cause a condensate trap.

 

[^woody^]

A centrifugal fan would be a lot better than a normal fan.

If you can't use an external wall, can't you install the fan in a window pane?

 

[hoyboy]

It's quite a small bathroom and only has a small window so want to avoid a fan here if possible as it'll block out too much light and be a bit to obvious... Plus every one I've seen so far is pretty ugly!

I'll use a high spec fan though - not a problem. i was going to lead it out through a square air brick that already exists in the wall. how do I join the ducking to this? The ducting will need to be the rectangular type as it's all that will run in the cavity available.. but I don't want to leave any areas that water could gather?

 

[Richard C]

I would forget about extracting through the air brick as it will seriously reduce the air flow, use a proprietary extractor fan shutter or grill. You can get square plastic ducting (Marley I think) but if you buy a 3m length of concertina aluminium fan ducting, you can make it any shape you want.

 

[hoyboy]

Thanks - I wasn't going to use the concertina type ducting as thought condensation might gather in the grooves. Do I need to worry about this.

The space available for the ducting is only about 60mm deep.

 

[^woody^]

If you have a condensation problem, then you should carry out the best remedy. If that is an 'ugly' fan in the window, but which is more efficient and effective than long narrow ducting and multiple bends, then that should be done.

When the fan is in use it is extracting moist air and not much will condense in the duct as the internal duct temperature and will be close to the bathroom temperature.
Condensing in ducting is only generally an issue in places like lofts where there is a colder external temperature than in the duct.

You've not mentioned ducting through the wall, so I assume this is a high-rise where access may be an issue?

 

[hoyboy]

Bascially, I've built out the wall - to hide cystern and shower pipes etc. I'm also lowering the ceiling to allow for spots and the fan (the ceiling is concrete at the moment). The ducting will need to go through the cavity left and then out an existing air brick behind where the new shower rail is.... I hope that makes sense....

You might be right about ugly efficient fans... but I'd rather a good looking adequate fan if possible!