Extractor fans ?

[ARWadsworth]

Did you seal all the joints with gaffer tape? The one I fitted is very quiet inside the house. You can hear it in the garden though.

Adam

[js.b1]

I've wanted to try one inlet above a microwave, then another to a gutted "designer" cooker hood. That way you can use a ****-off powerful inline fan, even a controller, which covers everything. Stick a waste disposal unit on the end and really go for it - burnt the toast, no worries, just wave it next to the intake and whooshhh.

[Andrew Gabriel]

What I don't understand with the inline fans, is why on earth don't they use a centrifugal blower rather than axial? Much more effective where you have the pressure drop of ducting to handle, and (can be) much quieter too.

[Tim W]

Andrew Gabriel wibbled on Tuesday 06 October 2009 14:19

Can't you get centifugal? I didn't investigate because axial is the only one that would fit between the wood upstairs (300mm or so gap) and even then I had to be careful to choose a really slimline one...

[js.b1]

I have wondered it too - however they might not be "axial".

Three fan types - axial, diagonal & radial...

- axial airflow - lots of airflow, relatively low pressure

- diagonal - lower airflow, higher pressure

- radial - lowest airflow, very high pressure

An axial & diagonal flow fan look identical - both "axial". The difference is a diagonal flow fan has an impellor which has a noticeable diagonal slant to the hub from one side to the other, thereby producing more pressure than a conventional "axial flow" fan. The disadvantage is they can produce a lot less airflow without RPM and often more noise with backpressure interactions (ducting).

I have seen a few "axial duct" fans which are in fact diagonal flow, they were pricey.

The new "trend" appears to be sticking the fan outside on the surface, so you can have 500-800m^3 without any noise inside. Not a bad idea, although sticking it recessed into the outer wall would be better re acoustic mass than surface.

The only difference for a diagonal-flow fan is the impellor. EBM-Papst seem to have reduced their range of "DV" fans, but I'm surprised the common Xpelair axial have not used DV impellors - probably because they are more interested in a micro-managed upgrade cycle of axial ->

radial (centrifugal) -> DC fan -> humidistat controlled -> air recovery expensive-box.

[the_constructor]

Having read all the advice offered, I have now purchased an Xpelair GXC6 and am going to contact the DG Installer and ask him to call round and measure up, now I know what size hole I want in the DG Unit.

Thanks all