A chimney is a drain
A chimney is the drain of flue gases. Once Stookten one indoors fire, the smoke left the house through small holes in the roof. That was the starting point for the first chimney: the roof gets a large opening to let the smoke through. To keep the whole house warm, the fire was fired in the middle of the house. Later, they developed the chimney that caught and drained flue gases, then the current flue came. The principle is that warm air is lighter than cold air. By placing a vertical column above the fire, the heated air rises rapidly and the smoke is sucked (this is also called ' Trek ').