I fitted a wood burner to my new build taking the flue out the gable wall on a 45 and up the outside. I put on stainless plates around the pipe coming out the wall and sealed it all with silicone.
I have had water running down the outside of the flue which has came in somehow and caused damp on the plasterboard behind the fire. I am not sure how I can seal it.
I was thinking of changing the 45 for a 90 out the back of the stove and making a new hole in the gable.