Cast Iron Air Brick Installation - What is the Best Method for Fitting?

[BarnsA]

I'm looking to vent both 1) a void under timber floors and 2) installing vent grills within the interior of a room - I've come across cast iron air bricks and wanted to find out how best to fit these:

http://www.castironairbricks.co.uk/prod ... k-9x3inch/

What would be the best approach here:

- Core drilling a series of holes through the external brick wall and covering with the fitting?

or

- Keyhole sawing a brick out of the wall right the way through into subfloor void area / internal room area and fitting the iron air brick flush?

Would this type of ventilation fitting require a duct?

Would the approach for doing the subfloor vents and internal room vents differ or would it be the same exact process?

Any advice on methodology and tools for the cleanest possible approach for either case would be appreciated.