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lookin for advice. Have removed old back bolier and pipes from fireplace and want to close off pemanently . I am looking to do job as simply as possible ideallly not having to do any work on actual chimney insulating open fireplace and simply dry lining wall can anyone offer advice on insullation and the best way to do said job also any pitfalls i may encounter

A redundant chimney leaves a cold single skin wall right in the middle of your room.
A single skin wall has the equivalent insulation of a single sheet of glass and as such being cold will attract any water vapour in the room, with a window this results in visible condensation – that you can wipe off. With a wall the damp goes into the wall makes the chimney damp, damp makes the chimney colder this attracts more water vapour and you end up with a cold damp chimney, that then strips the heat from the room.
The best solution is to cap the top of the chimney to avoid any rain coming down and to paint the outside of the chimney with a water vapour proof silicon to prevent any rain soaking in. This will cause the rain to run off the exposed part of the chimney rather than soak in. You may be lucky and have a correctly built chimney with waterproof tray that will stop the rain making its way down the chimney – look for a lead band just above the point where it comes through the roof..
Once you have capped the top and sorted any wind blow rain problems, then block up the fireplace and knock off all the plaster on the chimney inside the room (and any upstairs room the chimney may pass through) then stick polystyrene sheets to the chimney to insulate it and keep the warmth in the rooms and wet plaster over.
Of course if you have a cavity wall, with no insulation, then the single brick/block chimney will remain as bad as the rest of the outside wall and there is no point in adding insulation.

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