Air volume, air brick

[Russell griffiths]

Hi does anybody know how much air has to flow through an air brick 

I’m looking at using a round vent in stead of rectangular, and want to make sure it has the same flow rate if bco ask. 

Ta very much. 

[PeterW]

@Russell griffiths you may find this useful

 

https://www.bre.co.uk/filelibrary/radon/56998_jRadonSht2PP.pdf

 

1500mm2 per metre of wall according to this

[Russell griffiths]

Spot on @PeterW    ???