When I was a nipper I had a bit of a fascination with chimney pots, in fact I still do. I have a nice crown pot in the middle of the lawn that was given to me by a lovely lady some years back. I can just remember a neighbour having a chimney fire and it seemed to be making a sort of roaring noise, presumably by the flames from the burning soot pulling air up from inside the house. It was always fascinating watching our chimney being swept. The sweep would arrive remove the ornaments from the mantle piece, place his sheets over and then replace any heavier ones to keep the sheet in place. Once the brush was in place he would screw more sections and keep pushing, I think there must have been a hole in the sheet for adding more poles or canes until the brush appeared triumphantly from the top of the pot, with a whiff of soot. I think he had a vacuum to remove any soot that might have escaped but I don't ever remember much escaping into the room.