The chimney you are interested is between the room marked "Bed" and the room marked "Toilet" on Jeremy's diagram. This can be seen clearly on the photos of that side of the house posted in this thread. How does it help your argument?
As I say, I have identified the chimney which I believe was /is linked to the bedroom that I think Sheila was using before she went off her head. The bedroom in question was Jeremy's old bedroom, it has a fireplace and lo and behold we are led to believe by the police that the door to this bedroom was locked when they went / got into the premises?
How was it locked, and where did the police get the key from to open it up, and what did the police find once they got into that bedroom?