What is a chimney and flue?

29th February 2020


	What is a chimney and flue?


	Shop for Drain and Chimney Rods




			A chimney is a chamber through which smoke, hot gases, and other by-products of a fire are expelled from a building. A chimney usually has an internal liner called a ‘flue’ made from metal or clay tubing, although some older properties may just have a brick built chimney with no liner.

			Clay flue liners make ideal flower pots and are frost resistant. Using old clay flue liners is a great form of recycling and they can be stacked to make a creative display for your flowers and even trailing tomatoes.

			Flues are usually made from materials such as stainless steel, concrete or clay piping. Gases expelled from a fire or stove can be very hot and the flue protects the chimney brickwork and mortar.

			Not all flues are housed within a chimney, they may simply be fixed to the outside of a wall if a chimney is not available, as shown opposite.

			Types of flue liners
			Since 1966, all new chimneys must be lined during construction. There are many different methods and materials and all have their advantages and disadvantages. Chimney linings are typically made from metal, ceramic or concrete.

			Ceramic This is the most common type of flue in newly built houses. Ceramic flues may be round, square or rectangle in shape. The disadvantage of ceramic is that it has a very low insulation value so tar builds up easily. As it is fairly robust, ceramic can be cleaned with a wire or polypropylene brush and brushed vigorously without causing damage.

			Concrete A concrete flue is sometimes used on more expensive new build houses as it has the longest life expectancy of all flues, but it is more expensive than ceramic. It also has a high insulation value which reduces creosote and tar build-up. Concrete flues are very robust and can be cleaned fairly vigorously with either a wire or polypropylene brush, without causing damage.

			Metallic Metallic flues are made from stainless steel or aluminium and are either flexible or rigid and double or single skinned.

			Flexible metallic Flexible flues may be made from stainless steel or aluminium and be either single or twin walled. Stainless steel flexible flues are more expensive than their aluminium counterparts but have a longer life expectancy due to being more resistant to corrosion.

			A single skinned flexible metallic flue is basically a flexible tube made from either stainless steel or aluminium. Single skinned metallic flues should only be used on gas or oil boilers. Care must be taken when sweeping this type of liner and only brushes with soft bristles should be used to avoid damage to the inner surface.

			A twin skinned flexible metallic flue consists of an inner and outer skin and is suitable for gas, oil and multi fuel stoves. Care must be taken when sweeping this type of liner and only brushes with soft bristles should be used to avoid damage to the inner surface.

			Rigid single skin Rigid single skin metallic flues are made from either stainless steel or aluminium. Stainless steel is more expensive but more suitable for high efficiency boilers where a highly corrosion-resistant flue is required. Rigid metallic flues have a completely smooth interior surface so sweeping should be relatively easy. A brush with polypropylene or fine metal bristles is ideal for this flue.

			Rigid twin skin Rigid twin skin flues are often fitted where no brick chimney is present. The cavity between the outer and inner skin is filled with insulation to minimise creosote and tar build-up. Rigid metallic flues have a completely smooth interior surface so sweeping should be relatively easy, a brush with polypropylene or fine metal bristles is ideal for this flue.