En-suite shower install - chimney advice

[leemkule]

Hello,

I’m in the middle of building an en-suite bathroom (project is actually much further along than the picture).

The wall with the circle on it is part of the chimney stack.

Before this project, there was a ‘hit and miss’ style vent over the rectangular hole in the chimney.

The wall in question will be one of the walls of the new en-suite shower, which will be covered in tile backer board and then tanked.

My obvious concern is that if I just block up this hole I will cause ventilation issues in the chimney stack.

I had initially planned to put another hit and miss type vent in this location in the shower, but now that I think about it, I am concerned that humidity / water vapour from the shower may actually cause damp issues in the chimney since it’s in such close proximity to the shower, and that I would be compromising my shower wall tanking.

The tubing you can see hanging down is a 4 inch inline fan for what that’s worth.

We don’t have any plans to use the fireplace (one the other side of this wall and another downstairs) and may later remove the top of the chimney at the level of the roof.

Currently we’ve put a ‘draught excluder’ made of wool in the chimney above the fireplace, obviously to stop draughts.Any advice would be greatly appreciated, cheers.