Powerful wall extractor fan needed, any suggestions please?

[trickyex]

Can anyone recommend a really powerful fan for a shower room? It needs to be wall mounted as there is no access to the loft,
The room has a high ceiling and a power shower so I need something with a good flow rate. I would like it to be a quiet as possible, and am happy to spend a bit, up to £70 if needed.
My laptop is playing up today so I am struggling to do much internet searching. Builders need the fan ASAP so am under time pressure!
Many thanks

have you already got a hole in the wall? How big?

What is the ceiling height above the floor, in mm?

cheap weedy extractors as fitted by builders usually have an extract rate of about 80 cu.m/hr, and fit a 100mm hole. Don't get one.

five inch and six inch extractors typically have two or three times the extract rate, and can be quieter. When choosing, look at the extract rate and the noise in db. Bigger is better. You can get a speed control but it is expensive.

Here are some examples. This brand has a good reputation. Ceiling height is important.

six inch

five inch

I recommend a cowl vent on the outside, not one like a little plastic venetian blind, which will rattle annoyingly (until all the flaps fall off, which will not take long)

Thanks PigletJohn.
The ceiling height is approx. 3.4m, the fan will be mounted very high up the wall. The builders are going to use an existing grill (not sure why it is there) as its an old house with old plasterwork and it wil make it easier to fit, point noted re the vent, thanks.
Should have said that I would prefer a flush front and not a grille as I wont be able to reach it to clean/dust and I presume letting the fan get dusty would make it less efficient?
Do you have any other recommendations? I did email tlc but nothing back from them and need to order today! Argh....
Thanks very much.

Would either of the two flat fronted models on here be ok do you think?
www.tlc-direct.co.uk/Main_Index/Ventilation_Index/4_Inch_Fans/index.html?ad_position=1t1&source=adwords&ad_id=85865958797&placement=&kw=silent%20extractor%20fans&network=g&matchtype=b&ad_type=&product_id=&product_partition_id=&test=finalurl_v2&gclid=CL6kkOvl4MkCFSUewwodzEQAtA

Or this one with timer has a high flow rate
www.originalbathroomcompany.co.uk/html/Miscellaneous/Zehnder_Ventilation.htm