Ans - Chimneys work by drawing smoke and other gases up the chimney, using a draft created by a hot fire inside the fireplace. When the air revolves up around the outside of the chimney, it moves from a low-pressure area to one with greater pressure at higher altitudes. Since lower pressure areas are always trying to suck in more air from surrounding higher pressure areas (a centripetal motion), this airflow is called positive. Since upward flow creates cool downdrafts or down-drafts near chimneys that have fires going in them, these downward sections of chimneys are said to have negative pressure differential when compared to their surroundings - and areas such termed "chimney effect" components.