I have a Nectre Mk2 wood fire recently installed, the flue rises approx 700mm before entering an existing brick chimney via a 45 degree elbow with approx 400mm connection of flue before another 45 to finally exiting approx 1 m above the chimney. The chimney is on the centre pitch of the roof line. Whilst I always open both top and bottom dampers to feed in wood smoke billows back. Using dry season hardwood.
Would extending the flue another length help
to create more draw eliminating the smoke issue. Been advised flue length is as per makers recommendation.