spliting the extractor ducting

[colw1]

hi I have three ducts to go in in the loft for the main bathroom and two en suite , all of these ducts I want to run to the soffit but what I would like to know is if you can run all three toghter and out of one vent or at least two. Finally do I need any special equipment to get it in the soffit and what is best the white 100mm pipe or the silver

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[BS3036]

Generally they should go to separate vents, or you would need some kind of non-return value to ensure you weren't just venting into another room. I only have vented through a roof tile vent, which you may find easier than accessing the soffit. Or not.

 

[ban-all-sheds]

Don't forget the condensation traps

 

[pbar]

Yes, you can connect extractor ducting together to avoid multiple vents. But do not use one of the T connectors, make sure it's a Y connector with the angles very steep, otherwise you will be pumping from one room and some vapour will work it's way into another room. You can fit back draught shutters within the ducting though to help with that. I used this here, and didn't need those -

That has nice steep angles, so for extracted air to return to another fan, it would have to double back on itself. It won't do that, it will take the easiest route instead, which is straight on. You could connect a couple in sequence I guess for your three fans.
You can buy it from here -
http://www.diytools.co.uk/diy/Main/sp-1-979-32537-record-y-connector.asp
I didn't need condensation traps either, just make sure the fan overrun timer (if it has one) is on long enough to clear any vapour away completely.
It might be easier extracting through the roof, it was with me. In a lot of cases you can just buy a concealed tile vent, the same size as your existing tiles, so it's just a case of slipping a tile off, and replacing with the vented one. Make sure there's no timber behind the tile you take off though, as you'll need to cut a hole in the felt to take the ducting which connects to the underside of the tile. You might be able to reach a suitable tile from the ladders, if there is one you can remove close to the edge, and avoid having to climb on the roof.

 

[ban-all-sheds]

I'd advise checking with a H&V expert first - when a fan is pumping air into a duct it pressurises it - if two are working will the 3rd be able to pump against that pressure?

And even with angled joins might the pressure not push vented air into the other rooms?

Maybe a single in-line fan after the last room would be a better design?

 

[pbar]

I'd advise checking with a H&V expert first - when a fan is pumping air into a duct it pressurises it - if two are working will the 3rd be able to pump against that pressure?

And even with angled joins might the pressure not push vented air into the other rooms?

Maybe a single in-line fan after the last room would be a better design?

Perhaps though, when the two fans are running connected to the Y piece as the pic above, the third fan joining it would not find it any harder to push the air through, as the air already travelling in that direction will carry the air from the third fan along. The third fan is simply joining the air flow, not fighting against it. Or perhaps the place that sells the Y piece, also have a 3 part adapter too. I didn't look for that, as I only needed to connect 2 fans.

 

[ban-all-sheds]

Perhaps though, when the two fans are running connected to the Y piece as the pic above, the third fan joining it would not find it any harder to push the air through, as the air already travelling in that direction will carry the air from the third fan along.

Wow.

To think of all the money people have wasted on powerful computers to do CFD calculations....

 

[pbar]

Carrying on from this, you can buy a vent for extractor fans that will extract through the roof, which you can fit from the inside. So there's no need to go on the roof or disrupt the roof tiles in any way as it's all done from within the loft. See here - www.lapvent.co.uk and look under mechanical extraction.
That's an easy way to solve your extractor fan ducting vent issues.