It could also be made tall enough to clear the roof of the taller section of the house without being unsightly. In effect, the warm air pushes up towards the top of the house, creating higher air pressure there. At the same time, the pressure in the basement is lower than the pressure outside. The difference in pressure at various levels of the house is referred to as stack effect . This stack effect competes with a chimney that serves an appliance in the basement of a house.
Some houses make better chimneys than others.
Two or three-storey houses produce more stack effect than bungalows because their column of warm air is taller. Uninsulated, outside chimneys can reverse if the stack effect is strong enough, allowing smoke or cold outside air to spill into the house through the appliance. This form of installation should be avoided if possible. This type of chimney was developed to withstand the high temperatures produced by a chimney fire. The thicker insulation compared to other factory-built chimneys is needed to isolate nearby combustible material from the high gas temperatures in the flue.