So we have moved into a new flat (1700s) property. We have two chimney stacks on either end of the flat. Most of the openings where fire places have been boarded up, some with vents, some without. I have noticed a funny smell coming from one of the vents. The vent below it has no smell. The fireplace above is completed sealed up. It's difficult to describe the smell, it's sort of spur and musty. It's smells a bit like a museum. It's definitely not the smell of death. The air flow is good. The smell isn't very strong, it doesn't fill the room but you can smell it if you are within a meter of the vent. Any ideas what it could be?
Please see attached diagram. Pink floor is blocked up fireplace. Green floor is where the smell is coming from. Blue floor has odourless vent.