A chimney is usually built from masonry such as brickwork and is there to vent smoke and hot flue gases from a property’s heat source - such as a wood-burning stove, a furnace, a gas boiler, oil boiler or a traditional fireplace.

A chimney works by having a hole at the top that not only allows the escape of gases, but helps to create a flow through the chimney, thereby drawing fresh air into the room from an air brick or open window.  Air is needed in combustion as it contains oxygen, one of the three ingredients needed to produce burning.

Special clay fire blocks are used to line modern chimneys, as they have a smooth surface that prevents deposits of soot and tar from building up.  The chimney runs up through the house vertically, or as close to a vertical path as possible, to ensure a smooth flow of gases.  The chimney then runs up through the roof and surfaces in a ‘chimney stack’ on the top of the house. 

The taller the chimney pot, the better the air flow and the more efficient the chimney will be.  In fact, Chimney Pots came about as a result of the need to cheaply increase the height of a chimney.

There should be a chimney pot for each heat source that has a flue running from it.  When you look at the tops of houses, you can count how many chimney pots are on the top of the chimney stack and this will tell you how many flues are in the house.