I lived in three houses that had fireplaces, and every one of them would fry your face while freezing your fanny. I never felt rich enough to buy one of the glass enclosures.
The big problem with chimnies used to be creosote building up near top especially from lazy idiots banking fire with green wood. The large chimney in the kitchen would have top so nearly closed a cat could not have climbed through, let alone a sweep. I have seen flames shooting up twenty feet out of a chimney on fire, and if mortar had failed between any bricks lower down the pressure would send jet of flame sidewise into woodwork, and whole house would burn down.