Bathroom extractor - Getting out of roof space? Air Shutter?

[dhutch]

I need to fit a new bathroom extractor as the one that was in when I when I bought the house is broken and only vented to the attic space.

As its a large bathroom I want to use a 6inch inline extractor which will then need converting into something smaller/narrower to go down between the skelling and the felt and out under the eves.

Something like this isnt quite designed for it, but I presume it will do the job? Goes into a 200*60mm square duct designed to go out into an airbrick.

http://cgi.ebay.co.uk/ws/eBayISAPI....akeTrack=true&ssPageName=VIP:watchlink:top:en

Would you then expect there to be a shutter somewhere in the pipe/fan to prevent draught when the unit is switched off?

Rather than having it on an auto timer I though I would put it on a separate pullcord so it is only on when your showering not if someone uses the loo in the middle of the night.

Daniel

 

[stem]

The picture below shows how it's normally done. The link you have posted is really for a Kitchen Chinney duct system, not a bathroom fan. The flexible part goes down inside the chimney to the fan connection, and the rectangular duct is designed to lay flat on the top of the kitchen units and be out of sight. Rectangular duct presents a higher resistance to airflow than circular duct. Whilst this is not a problem for a chimney as they have centrifugal fans which generate a higher pressure and can overcome the extra resistance. Axial fans (blade type) do not create such a high pressure and duct resistance is more of a problem.

Flexible circular PVC duct can be squashed slightly to get it through to the eaves. Be careful not to tear it when pulling it through.

You can buy back draught shutters that can be installed in the duct, but some fans come with them already. Make sure the fan you buy is suitable for ceilling mounting. It will have shutters that do not rely on gravity to operate as some wall mounting fans do.

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• stem
• 22 Sep 2010
• 6

Alternatively

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• stem
• 22 Sep 2010
• 4

With this solution, you should lag the duct to stop condensation forming in the vertical run through the roof space which could run back down through the fan. In severe cases usually where there is a long run of duct through the roof you may need a condensate trap at the bottom to.

If the existing fan vents into the loft space, it must be a very well ventilated loft, otherwise I would expect you to suffer at best damp on the ceiling and at worst for the roof timbers to have started rotting.

 

[dhutch]

The picture below shows how it's normally done. The link you have posted is for a Kitchen Chinney duct system. The flat duct is designed to lay flat on the top of the kitchen units and out of sight.

Flexible circular PVC duct can be squashed slightly to get it through to the eaves. Be careful not to tear it when pulling it through.

You can buy back draught shutters that can be installed in the duct, but some fans come with them already. Make sure the fan you buy is suitable for ceilling mounting. It will have shutters that do not rely on gravity to operate as some wall mounting fans do.

If the existing fan vents into the loft space, it must be a very well ventilated loft...

I've seen it done that way with a 4inch duct just deforming a bit but I cant see you getting a 6inch one down a 4inch gap without a lot of struggle which is why I was looking at the flat/rigid ones as a way of making it an easier job and still having a decent cross section to the get the air down.

I was going to use a 150mm inline fan which would allow me to soft mount it and keep some of the noise transmission down.

Something like this
http://www.ebay.co.uk/itm/6-150mm-L...arden_Hearing_Cooling_Air&hash=item58935a5653

The sofets not pretty or about to be replaced, so im not overly worried what the exit looks like.

Loft isnt any more/less ventilated than any other, hence moving it. I dont think he ever used it and it wasnt wired in when I moved in.

Daniel

 

[stem]

Sorry I missed the 6" bit. However, if you reduce the duct size down to get it outside there isn't really much benefit in fitting a larger fan as you will restrict its air flow, so might as well fit a smaller model anyway.

Also, the size of the bathroom isn't seen as a factor so much these days. As much steam is produced by a shower in a big bathroom as a shower in a small bathroom. You could always fit a smaller fan and leave it running for longer to shift the same volume of air as the larger one would, albeit in a shorter time.

If you really want to use a 6" fan then don't restrict the flow by reducing the crossectional area of the duct. You could run 6" duct from the fan close to the eaves and then add a "Y" connector to connect two 4" ducts that go outside separately. Xpelair make a Y Piece Splitter - 2 x 100mm to 1 x 150mm part number - 91282AA

 

[dhutch]

Xpelair make a Y Piece Splitter - 2 x 100mm to 1 x 150mm part number - 91282AA

Thats good infomation, and would be easier to terminat neatly than the rigid square duct.

 

[foxhole]

I have a 6inch fan with twin inlets and single outlet all 4inch with a Y joint, work fine, there is very little resistance by reducing the outlet as it's an open grill.