The key use of a chimney is to safely remove the elements of combustion from a fireplace to the outside atmosphere without causing any danger to the occupants of the building. Hot air rises from high pressure to low pressure, and gases move from the fire upwards out into the atmosphere, which is the fundamental way chimneys operate. This method of design has remained unchanged since the invention of chimneys.
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The History of Chimneys:
The Romans used tubes inside internal walls to draw smoke out of their bakeries. However, chimneys are thought to have appeared in the 12th century, usually in very large buildings and grand homes. The earliest recorded chimney in the UK was thought to have existed in 1185. It was not until the 16th and 17th centuries that chimneys became common in homes across the land—some 1,700 years after the Roman Empire was founded! Industrial chimneys became common in the 18th century.
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Chimneys in normal homes and buildings were originally built of wood and plaster or even mud, but later from brick or stone. Chimney pots were designed to control any downdrafts. These have become an iconic look of many roof tops depicting days gone by.
Chimney Terminology:
Most people know very little about the elements of a chimney and the associated terminology. Most are aware there is a tall structure that allows smoke to escape, but that’s about it. There are a few more things to a chimney, such as:
A Flue – This is a duct or a pipe which smoke and products of combustion are removed from the fire to the outside atmosphere. The term flue in the past actually meant chimney.
A Flue pipe – This is a metal appliance used to connect an appliance to the flue in a chimney.
Chimney – This is the actual structure surrounding one or more flues. A chimney is usually the only visual element someone would see as the rest is hidden from sight.
Chimney terminal – This is the pot (chimney pot) which is found at the top of the chimney.
The European Standard BS EN 1443: 2003 Chimneys – General Requirements, categorises chimneys and flues into three basic designations:
Custom Built Chimneys – Built on site using factory made flue liners.
System Chimneys – Prefabricated chimney systems. Made in a factory and put together on site. The main advantages of chimney systems are their off-site production and preformed insulation.
Connecting Flue Pipes – Specifically designed to connect an appliance to the flue or chimney.
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What are the differences between a conventional and a balanced flue?
Conventional Flues – Fires with conventional flues rely on the natural circulation of air in a room to remove gases from combustion. They work with traditional open fires and glass-fronted fires. The air which is needed for combustion is supplied from the room the appliance is installed in.
Ventilation points are needed at the front of a fire that has a conventional flue, so it can essentially “breathe” and assist in the convection of the radiant heat from the fire.
Conventional flues are not quite as efficient as balanced flues as they draw in air from the (warm) room. This air, which has already been or is being heated by the fire, will be taken away to aid in the combustion process. Although not as efficient as balanced flues, this is a perfectly natural process that comes from combustion and the requirement for the use of air.
Balanced Flues – Balanced flue fires are more efficient than their conventional flue counterparts as the fires are totally sealed from the room. Essentially, there is no drawing of air from the room, which impacts efficiency.
With a balanced flue, the air is taken into the fire via a twin outside pipe (not from the room) mounted on an outside wall towards the rear of the fire. The removal of combustion gases exits from the second vent in the wall to create an ultra-high-efficiency heating method.
A balanced flue is an ideal solution when you don’t have a conventional chimney. These tend to be more common in newer build properties.
Why Do We Line Chimneys?
Chimneys that are not lined or systems that were constructed before 1965 may need a modern lining for a range of reasons. The original flue may have deteriorated and could be leaking smoke into rooms or other parts of the building. Sometimes tar can seep through the walls of the chimney and cause staining on the walls in the building. A system which is defective and well past its best can contribute to a poor updraft. An updraft is where hot air rises. Any form of debris or friction in the chimney can cause a poor updraft and, as a result, a poor flow of gases.
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Chimney Renovation
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Renovating a chimney is a specialist job. The renovation procedure can be achieved in a number of ways. Insulating concrete can be pumped in and around an inflatable former – allowing for a chimney funnel to be newly created. A stainless steel flexible liner can also be lowered down, or a spray-on coating or ceramic coating can be used as an alternative. Prices for renovating a chimney can vary depending on a wide range of factors, including the size, the condition of the chimney, and, of course, the renovation technique you wish to opt for.
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Chimney & Building Regulations
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Currently, there is no regulation requiring how an existing chimney should be lined. However, it should be done by a competent person or approved by your local area Building Control if it’s being done in conjunction with the installation of a heating appliance.
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Chimney Faults
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If you are having your chimney swept by a chimney sweep, they should inspect the chimney for a range of faults and issues, some of which include:
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1. Protruding cement at the joints
2. Masonry damaging the liner
3. Blocked terminal
4. Liners fitted upside down
5. Damage through incorrect sweeping
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