Installing kitchen extractor fan in wall at internal 90deg corner to flue outlet. Working backwards checked flue site requirements but no mention of proposed configeration. Flue is 2.5m from floor and 450mm out off corner, proposed siting for fan would be 550mm from corner approx same height on adjacent wall. Boiler is 31kw balanced flue. Dont want to knock 6" hole in wall if not suitable! Have tried Baxi, no help. Any ideas?