Do they exist? I want a square one (as I’m replacing a standard vent axia) as the hole is already there but want something that has some form of closure mechanism on it so it doesn’t allow air to whistle through. Only other requirements are that it doesn’t cost the world and that I can have it on a delay timer connected to light switch!

Any suggestions

Can’t help you with square but I have one of these
http://www.rselectricalsupplies.co.uk/mobile/airflow-icon15-circular-extractor-fan-72683501_5807?gclid=CIXopaX-wMECFbPJtAodR2AApw
When you switch it on the iris opens and when you turn it off the iris closes.
Maybe you can get a square patress or make one.

I’ve got a vent thing that goes on the exit that opens when the fan runs. Not very hi tech but it seems to work.

A lot of them comes with a butterfly flap that opens when the fan comes on, but prevents back draughts.
You can buy them individually to fit into the ducting, rather than being integral to the extractor. Never seen a square one though…

I’ve got a Ventaxia one with a built-in shutter – might be this:

http://www.screwfix.com/p/vent-axia-va100x-20w-axial-bathroom-fan/83393

Has worked fine for nearly 10 years (kiss of death… 🙁 )

erm…

three new pounds

surely the outlets round – even if the fan is square ?

those manrose flap things are noisy as **** in the wind…. i pulled mine off and fitted a normal shrouded vent

http://www.screwfix.com/p/manrose-cowl-vent-white-140-x-140mm/16195

and a butterfly valve in the pipe. – voila no draft.