In Line Extractor Fan Advice Please

I am looking to install an extractor fan for a bathroom project. Based on Vent Axia calculator and others, the cheap and cheerful 4" wall mounted versions pushed by the sheds is somewhat lacking. I am therefore conidering an in line fan with 5 or 6" ducting via the loft to an end wall outlet.
My questions are:
How to terminate the duct through the wall - previously I have used a wall terminal kit consisting of an external grill, a wall sleeve and a spigot plate so that the ducting can be taken from a fixed connection at the wall. I am struggling to find one for ducting larger than 4". Can anyone recommend a supplier, or advise a suitable alternative?
Vent Axia offer a mixed flow fan ACM range. These look pretty good but I am being quoted 110 (+ 35 for timer) for a 6" version!! Are they worth the big bucks?
Any general advice on ducting installation would be gratefully received.
TIA
Phil
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The alternative is to fit two 4" fans, which are cheap and readily available. In our main bathroom we have two in-line fans. One grille in the ceiling is over the loo, the other over the bath. They use flexible pipe to connect to the in-line fans in the loft and then discharge out of plastic vents in the soffits.
HTH Dave R
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When using ducting, always use a centrifugal fan. Axial flow fans get good flow rates, but are unable to produce a significant pressure differential, which is what is need to promote flow through a duct. Centrifugal fans may produce lower flow rates, but they can really push against resistance, which is what is needed here.
Christian.
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Thanks to all for age advice and confirming my thoughts.
Phil
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On Wed, 20 Aug 2003 09:04:48 +0100, "TheScullster"

guide as a downloadable .pdf file from the Domus website when I was working on a kitchen (I also wanted a larger than standard duct and components.) I think their website will be www.domusventilation.com I could not find anyone who held stocks of the parts but once I found their number for a kit, I was able to order it through a local builders merchants who stocked the standard size components.
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Thanks Brian - that Domus info is most useful
Phil
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