I have a 3 storey victorian house with a stack with six chimneys in it (all are capped with pepperpots or some other cowling). In order to find out which fireplace was attached to which chimmey I put a smoke pellet in each fireplace. In one test on the ground floor fireplace, smoke came back down the flue into the upstairs bedroom fireplace. There is also some smoke leakage through the pointing which need replacing. Question 1. Obviously smoke will not be able to leave the chimney properly because of the pepperpot but does the fact that it came down the flue into the bedroom mean, catergorically that the flue has failed somehow and is leaking into the adjacent flue (because i dont think it was coming out of the pepperpot and down into the adjacent chimney? Or Question 2. Do flues ever join before going out a chimney (thus smoke was merely finding the easiest escape route)?