Question about a ventilation vent

[Behoove]

The chimney breasts downstairs need to have air vents installed to prevent damp. (Have closed off the chimneys to make a loft conversion)
Do the vents go in the skirting board or into the brick of the wall?

Usually in the brickwork, low down, with a brick-sized plastic, brass or alumium grille.

The plastic ones are easy to paint (before fixing).

The chimney needs a vent top and bottom.

Thanks (again) piglet