Direct I think. Fan on wall inside, hole thru wall, grille on outside. It's the bit out the back of a victorian terrace so both walls are external.
Presumably the boiler flue is out through the wall with A? If it was B, you'd fall foul of the 30cm from opening.
B would probably be easier to wire it too.
@Kurai started
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Direct I think. Fan on wall inside, hole thru wall, grille on outside.
It's the bit out the back of a victorian terrace so both walls are external.