One of the things that has happened historically when teams have left embassies is that they burn confidential documents that they can’t take with them.What's the theory like? That chimney looks well used to me.
Presumably the heaviness of the smoke suggests inefficient burning, like paper and flame, rather than an efficient system, like maintained heating.
Doesn’t mean anything in and of itself but would be one of the sort of things that would be looked out for.