nonymouse wrote:
If you have four chimney pots, it would be unlikely that you don't have
four flues.

Sorry to be a bit of a muppet here but how do I fit air bricks then to
ensure the air flows through the height of the house? Can I simply fit
them both 20cm in from the left of the chimney breast and assume that
will allow movement of air between the floors and the chimney?


You just want to put them where the old fireplace would have been,
wherever that was. Not necessarily central on the chimney breast if
there are several chimneys and back to back like yours. Put it low
down, but not as low as the one I've just had to reposition when
refurbing a room recently: the old grille was completely occluded by
soot and debris which had fallen down the chimney!

David