Bathroom Extractor Fan - How long can ducting be?

[xreyuk]

Hi,

My bathroom extractor fan has broken, and I've fitted a standard inline extractor fan in the loft, as that's what was in.

We have approximately 2-2.5m of ducting between the bathroom ceiling and the fan, and then about another 2-2.5m ducting before it hits an external vent.

After fitting the standard fan, I've read that these fans should not be used with more than 3m of ducting, and I have between 4-5m. Will I be okay with this fan or should I buy a centrifugal one?

 

[JohnD]

is it a weedy little 80 cu. m / hr. fan, or a manly 240 cu.m/hr one?

can you see it here?
http://www.screwfix.com/search?search=inline+fan#_=p

 

[xreyuk]

is it a weedy little 80 cu. m / hr. fan, or a manly 240 cu.m/hr one?

can you see it here?
http://www.screwfix.com/search?search=inline+fan#_=p[/QUOTE]

It's not there cause I got it from B & Q and it looks like it's 85 cu. m/hr

 

[JohnD]

bin it and get a proper one.

 

[xreyuk]

Any suggestions for what I should I get?

 

[JohnD]

the ventaxias on my previous link have good reports

there are some cheaper makes here
http://www.tlc-direct.co.uk/Main_Index/Ventilation_Index/4_Inch_Fans_Duct/index.html

Look at the extract rate, and at the noise (db) rating, as well as buyer comments.

 

[xreyuk]

the ventaxias on my previous link have good reports

there are some cheaper makes here
http://www.tlc-direct.co.uk/Main_Index/Ventilation_Index/4_Inch_Fans_Duct/index.html

Look at the extract rate, and at the noise (db) rating, as well as buyer comments.

Thanks.

Would 110 cu. m/hr be enough or should I go higher?

Maybe this one? http://www.tlc-direct.co.uk/Products/SLTDK250T.html

 

[Deleted member 174758]

Going higher is all very well, but there will still only be so much air you can pull down a length of pipe of a given (restricted) size. If your fan is too big it will simply overheat and die prematurely because it will be trying to overcome the frictional losses in the duct. One way to makemore efficient use of a small fan is to forgo the flexible concertina plastic ducting supplied with many in-line fans and instead fit smooth bore hard plastic ducting (e.g. soil pipe or smooth bore ductwork) and to seal all the joints with silicone. Not sure if that's the case in your installation, though

 

[xreyuk]

Going higher is all very well, but there will still only be so much air you can pull down a length of pipe of a given (restricted) size. If your fan is too big it will simply overheat and die prematurely because it will be trying to overcome the frictional losses in the duct. One way to makemore efficient use of a small fan is to forgo the flexible concertina plastic ducting supplied with many in-line fans and instead fit smooth bore hard plastic ducting (e.g. soil pipe or smooth bore ductwork) and to seal all the joints with silicone. Not sure if that's the case in your installation, though

Thanks.

I'd probably look into that in the future but not sure how good I'd be at doing that myself. It'd be a bit of a job to navigate it no the route in the loft.

I'm between these two, could anyone advise which they think best, considering I'm using the flexible piping?

Looking at the spec sheets it links to, I'm leaning towards the TD160 as it's £20 cheaper. Also not sure about getting the TD250 bearing in mind the above post.

TD160 - http://www.tlc-direct.co.uk/Products/SLTD160T.html
TD250 - http://www.tlc-direct.co.uk/Products/SLTD250T.html

 

[JohnD]

A more powerful fan will shift more air through the duct.

I don't believe that will cause it to overheat (unless you jam a screwdriver into the blades to stop them turning)

 

[xreyuk]

A more powerful fan will shift more air through the duct.

I don't believe that will cause it to overheat (unless you jam a screwdriver into the blades to stop them turning)

Thanks.

I've since found the Manrose MF100T which is a fair bit cheaper so might go for that. Any thoughts on Manrose?

Finally (sorry for all of hte questions) The current ducting runs underneath the loft insulation in the loft, but this has caused a sort of 'pinch' in the ducting meaning poorer airflow.

Can I run the ducting above the insulation, or is that a no no?

 

[JohnD]

Yes you can, but if it is cold condensation will form inside it. Straighten it out and buy a small roll of loft insulation, flop that over the duct or wrap it.

Rigid duct is not such a problem because you can slope it a little so any condensation runs outside, but the flexible hose accumulates dust, fluff and water.

 

[lbzbean]

I just fitted a Manrose MF100T running through about 5m of duct, works great.

 

[xreyuk]

Cheers, thanks for the info