On Tue, 28 Jan 2020 23:10:45 +0000, alan_m wrote:

On 28/01/2020 22:31, polygonum_on_google wrote:


You could try a cowl vent or flap vent as shown he
https://www.screwfix.com/c/heating-plumbing/air-vents/cat840496

Some cowls also have the inbuilt flap that only opens with airflow from
one direction

https://www.toolstation.com/round-du...-outlet/p18869

I have one fitted to an extractor fan BUT I had to shave around a
quarter of inch off the bottom of the flap to give more clearance so it
operated smoothly.

Note: the link above maybe the wrong size fitting for your ducting

SF doesn't seem to have a cowl vent suitable for 150mm - I'd guess that most
ext. fans for kitchens are 150mm - cooker hoods could be smaller.
I used the 'giant' version to ensure that the open area was a lot bigger
than the opening of the fan. Selection he
https://www.toolstation.com/ventilat...s-grilles/c376
--
Peter.
The gods will stay away
whilst religions hold sway