*Pigletjohn* is there a max duct length to vent an extractor

[another20]

Kitchen extractor fan - duct would need to run 5m to the external wall - would this even work or be efficient - would a recirculating one work?

I was investigating this recently - it depends on your extractor fan. Most will tell you how long the duct can be. Each 90 degree bend reduces this considerably - but again, exactly how much depends on the, but typically by around 1m I believe.

I have an elica hood which was rated at up to 9 meters.

That’s great to know that I can look at the appliance. Will just be the one 90 bend from above hob where it needs to turn horizontal into the ceiling

You can get tables over duct length. But some of the Elicas have powerful fans. See if yours is a twin motor design.

If you can't find the spec, email them to ask about duct length and diameter. It will probably be 125mm but might be 150mm.

Rigid duct is much better than flexible.

It will be a hundred times better than a recirculating hood.

You can also get extractors where the fan and motor are mounted on the outside of the wall, they are quieter.

if you are using a long duct through a cold space (loft, etc) then the warm moist air being extracted can cool and condense in the duct - consider insulating the duct if this is the case as you don't want water running back into the extract fan

Thanks - what spec should I be looking at eg what power or motor type.

I do want it to be quiet as possible as it is a large kitchen / diner / lounge space 5x11m.

So I could put the motor on the wall in the corridor behind the kitchen and the fan on the external wall outside ? Or are they together?

motor and fan are same unit - look at 'in-line' fans like this one
www.tlc-direct.co.uk/Products/SLTD500SILENT.html?source=adwords&ad_position=&ad_id=315107931576&placement=&kw=&network=u&matchtype=&ad_type=&product_id=SLTD500SILENT&product_partition_id=336986752000&version=finalurl_v3&gclid=Cj0KCQjwg73kBRDVARIsAF-kEH9KNogqC9gHpf0m7JPNK_NWEos_vt75Vu-OHtCOtLtZUS8TH4rBm4oaAhQ9EALw_wcB
as an example (first one I found one google - no recommendation but for illustration)
In Scotland, we need a minimum capacity of 60litres/second for kitchens (which generally equates to a 6" fan) but this is reduced to 30litres/second if it is a hob hood extract.
I'd go for the sweet spot between largest capacity and lowest noise.

Sorry I can't remember.

The Elica website is awful, but they do a good glossy brochure. Email and ask for that.

There is a link to extraction data on the TLC website
Scroll down and look for "hood size calculator"

www.tlc-direct.co.uk/Main_Index/Cooker_Hood_Index/Built_In_Canopy/index.html on the "external motor unit" one

More variety on www.tlc-direct.co.uk/Main_Index/Cooker_Hood_Index/index.html

And the ducting brochure under "brochures and instructions"

Use 150mm round duct, or the 220x90 rectangular duct, keep it as straight as possible. The resistance of the larger duct is a lot lower.
Make sure everything is fitted soundly to avoid noise. Also having a short leg of isolating duct between the fan and rigid duct can be very helpful for nose.
Don't use flexible duct though. We used semi rigid metal duct rather than flexible where it was essential.