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Last edited 22 Dec 2023

Keeping chimneys and flues clean, not only for Christmas

[edit] What is a chimney? What is a flue?

A chimney and flue is a structure, often part of a building, sometimes separate or installed as an additional element or self-supporting tube (such as a gas flue). The hollow void within the brick, stone, concrete, metal, or prefabricated chimney is referred to as the flue. The flue connects to a combustible heat source, such as the combustion of gas in a gas boiler or solid fuel used in open fireplaces, wood-burning stoves, and biomass boilers.

[edit] Does Father Christmas come down the chimney?

If he can, obviously yes, he does, but if the chimney is closed or there isn't a chimney, he will, for sure,find another way.

[edit] Agios Nikolaos

While many stories pervade history in different cultures, the earliest link to Father Christmas, Sant Claus, St. Nicholas, or Sinterklaas and the use of chimneys seems to trace back to a 4th-century Greek bishop from Myra, now Turkey. This Saint was credited with miracles. In one tale, the saint he met a poor man on the brink of selling his own daughters into slavery, and under the cover of darkness, he anonymously threw three bags of gold down the chimney to provide dowries for the girls. The gold landed in their stockings, which were drying by the fire.

Agios Nikolaos or Saint Nicholas in scenes from his life by Theodoros Poulakis estimated to be from around 1650. From the collection of the Hellenic Institute of Byzantine and Post-Byzantine Studies in Venice.

Illustration of a brownie by Alice B Woodward, from "Brownies and Other Tales", by Juliana Horatia Ewing, published by G. Bell & Sons, London, 1920.

[edit] From witchcraft to folklore

In the 1400s, the fear, rather than joy, that magical creatures could enter homes stemmed from stories of witchcraft, which were supported by a prolific book on witchcraft, Malleus Maleficarum, from 1486 by Kramer and Sprenger, which described witches entering houses through chimneys or windows.

In Scottish folklore, a brownie, broonie, household spirit, or hobgoblin is offered a bowl of milk or cream by the hearth and said to come out at night to perform various chores and farming tasks. They may leave a home forever if insulted or taken advantage of.

In Scottish and Irish folklore, a bodach is a bogeyman who comes down the chimney to kidnap naughty children.

In Germany children should clean their shoes on the 5th of December and leave them outside the front door or by the fireplace for St Nicholas to fill with sweets. While in Italian folklore, ´La Befana rides on a broomstick and may deliver candy to good children via the chimney.

Chimney La Befana Bartolomeo Pinelli 350.jpg

"La Befana" an etching on laid paper from 1821. Bartolomeo Pinelli.

Illustration of a visit from St. Nicholas dated 1844 by Clement Clarke Moore.

[edit] 'Twas the Night Before Christmas...

In 1809, Washington Irving, wrote the book ;Knickerbocker's History of New York', in which he describes Saint Nicholas as a man who is seen "riding jollily amongst the tree tops or over the roofs of the houses, now and then drawing forth magnificent presents from his breeches pockets and dropping them down the chimneys of his favourites." But it was the poem of 1822, 'A Visit from Saint Nicholas', by Clement C. Moore, that established a Father Christmas or Santa Claus who entered homes through the chimney; today, the work is more commonly known as 'Twas the Night Before Christmas'.

[edit] How do chimneys and flues work?

The chimney, folklore or no folklore, in combination with the flue, removes exhaust fumes, or smoke, from the place of combustion, away from the internal spaces being heated. It draws pollutants through a wall to the structure at the side of the building or running up through the roof into the upper air surrounding the building, and into the atmosphere. In many cases, a cap, cowl or wind cowl located on top of the chimney prevents wind from blowing downward, which can hinder the exhausts from leaving the chimney. Because historically most buildings had chimneys and fireplaces were of the heart of home life, they often became architectural features.

Chimneys function because hot air rises, so the hot exhaust gases create a pressure difference between the flue inside the chimney and the room. This pressure difference causes the fire to draw (or create a draft), which means warm air is pulled up through the chimney, drawing or pulling air from a vent or the room to feed the combustion (requiring oxygen), which then heats and is pulled up the chimney along with the exhaust gases in a continual cycle as the fire burns. Controlling the level of fuel and the rate at which oxygen is fed to the fire helps control the rate and temperature of combustion.

[edit] What happens after leaving the chimney or flue?

The warm exhausts from a chimney rise upwards until cooling, at which point the pollutants within the exhaust spread out, gradually mix with the air, and become part of the atmosphere. At relatively low levels, the pollutants from chimneys and flues are diluted by the surrounding air and become less harmful, though increased concentrations are problematic, and extreme levels can cause smog. Smog is a low-level dense cloud caused by high levels of pollutants in the air. Smog occurs when water vapour 'sticks' to the particulates released by burning fuel, in particular standard coal. This reduces visibility and can cause health issues for those exposed at the ground level.

[edit] Substances emitted from chimney and flues

The types of substances that are emitted from gas flues connected to household natural gas-fired boilers can include:

Nitrogen oxides (NOx)
Carbon monoxide (CO)
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Volatile organic compounds (VOCs): benzene, formaldehyde
Trace amounts of sulphur dioxide (SO2)
Particulate matter (PM), including PM2.5

The burning of wood is sometimes considered preferable to gas because it can be renewed and carbon released on burning sequestered when replacement tree stocks are planted. The type of wood burner or biomass boiler that is used, as well as the type of fuel can affect the amounts and types of pollutants dramatically. Coal, smokeless coal, fresh wood or kiln dried wood, may emit the the substances listed above, along with those below to vary varied degree:

Particulate matter PM10
Polycyclic aromatic hydrocarbons (PAHs)
Sulphur dioxide (SO2)

Gas flues can suffer from a build-up of acidic substances, top residues falling inside, as well as natural build-ups like cobwebs, all of which can reduce the efficiency of their draw and, in the worst cases, create blockages that can be lethal. In the UK, gas boilers should be inspected and cleaned annually.

Chimneys and the flues within them from open fires, stoves, and biomass boilers can form a layer of creosote on the inside, which is highly flammable, which can increase the risk of chimney fires and reduce the draw efficiency of the chimney. Creosote is a carbonaceous chemical formed by the distillation of various tars and the pyrolysis of plant-derived material. Generally, there is coal-tar creosote, created by coal and smokeless coal, and wood-tar creosote, created by wood fires, or a combination of the two.

[edit] How were chimneys cleaned historically?

Until the introduction of gas and electricity, the burning of coal and wood was one of the only sources of heat in the home. Traditionally, almost all houses had chimneys, sometimes lined and with hollow flues, as can still be seen on historical buildings. The job of cleaning the chimney was often and still is down to the local chimney sweep.

Historically, many chimney sweeps were referred to as climbing boys or climbing girls, as children, due to their size, could enter the chimneys. Today, children are not used to sweep chimneys, and both chimney sweeping and flue maintenance can be carried out by qualified technical professions.

[edit] The climbing boys

The story of climbing boys remains part of a shameful history, which was poetically depicted by William Blake in his books 'Songs of Innocence and Songs of Experience' in the late 1700's. The Society for Superseding the Necessity of Climbing Boys (SSNCB) was founded in 1803, and an active campaigner against the employment of climbing boys, Joseph Glass, invented, but did not patent, a flexible cane rod system for cleaning chimneys in 1828. The Chimney Sweepers Act was introduced in 1834, followed by the Chimney Sweepers and Chimneys Regulation Act of 1840. In 1863, the publication of 'The Water Babies', a novel by Charles Kingsley, with its main character Tom, helped raise public awareness about the mistreatment of climbing boys.

[edit] The last climbing boy

In 1864, the Chimney Sweepers Regulation Act was introduced; however, it wasn't until 1875 that the last of the climbing boys died. A 12-year-old chimney sweep, George Brewster, working on the Fulbourn Hospital chimneys, got stuck, and despite a wall being removed to rescue him, he died shortly after. He became the last climbing boy of England, the last to die cleaning chimneys, as a bill in September of the same year finally stopped the practice of using children as chimney sweeps.

[edit] How can chimneys and flues be cleaned today?

Today, many houses continue to use and need chimneys, especially older houses. These chimneys need cleaning, and while there is a list of improvements that can be made to fuels, stoves, and flues, chimneys emit dirty gases by their nature, so in effect, they are not clean. The cleanest chimney or flue is one that is surplus to requirements, not needed, used minimally, or effectively not there, though there are many strong practical arguments for the necessity of wood fires in certain areas as well as their cultural and aesthetic significance.

There are a different number of effective ways to help clean a chimney, or at least the emissions coming from it:

Insulate the building as well as you can to reduce the need for heating and the amount of fuel required.
Use certain fuels; coal and wet wood create more pollutants, followed by smokeless coal and then kiln-dried wood.
Use a stove fan to help distribute the heat evenly.
Manage the stove correctly; stoves running in slumber can create more emissions.
Install a stove heat recovery pump. These innovative systems can help increase the efficiency of existing stoves,reducing the fuel used.
Replace the stove with a modern Ecodesign-compliant or DEFRA-exempt stove.

[edit] Fabric and design to reduce demand

In newer properties, correct design and construction can help minimise the heating requirements of homes, while refurbishment and retrofit in older homes can significantly reduce the demand for heating. This might include; improving the performance of the fabric, triple, double, or secondary glazing, closing up drafts and insulating lofts, retaining heat while replenishing air (MVHR), designing to maximise natural solar energy, or the use of static ground temperatures. Other options may include using solar thermal to preheat water or using renewables along with a heat pump to remove the need for combustion.

While these interventions, despite cost considerations, should be almost standard in new buildings, they can be more complex in existing properties. For example, heat pumps generally run at their highest efficiency at lower temperatures and, as such, are used in combination with significant fabric improvements. Wood burners, biomass systems, and gas boilers, on the other hand, can run at higher temperatures.

[edit] Keep the chimney or flue swept

The most basic chimney cleaning equipment available today still relates to the designs of Joseph Glass, but modern-day chimney sweeps have the addition of powerful vacuums and innovative designs. Most solid fuel chimneys are cleaned from the bottom up using brushes and vacuums, though they may be employed top down, effectively protecting the hearth and scrubbing and vacuuming the flue. Domestic gas flues might use a version of the industrial process called scrubbing, which adds certain substances to a warm flue to remove oxides from its internal surface.

[edit] Using certain fuels

The type of wood that is burned can have a significant impact on emissions; for example, kiln-dried wood can emit around 70% less PM 2.5 than untreated wood. This is a comparable figure to that of smokeless coal; when compared to ordinary house coal, smokeless coal releases up to 20% less carbon dioxide, though both are fossil-based and therefore non-renewable. This is why prepared wood is considered to be a preferable fuel to any type of coal.

[edit] Stove top fans

Stovetop fans can help better circulate warm air from a stove around a room. Heat from the fire travels up the base of the fan to heat a Peltier device underneath the fan blades, causing thermoelectric energy that turns the blades and circulates the warm air around the room.

[edit] Stove heat recovery pumps

Pumped air heat recovery systems for stoves couple an air pump to a heat-recovery element set in the bottom of a stove flue, forcing a jet of heated air from the front of the flue just above the stove. This then entrains and circulates the heat rising from the stove to increase the volume and distribution of warmth around the room. The positive pressure this creates in the room can then be distributed out into the rest of the house to create convection flows of warm air that will circulate to a far greater extent than can ever be produced by the stove on its own.

[edit] Replacement with a Ecodesign compliant or DEFRA-exempt stoves

Newer replacement ecodesign-compliant stoves or DEFRA-exempt stoves can dramatically reduce pollution levels as well as improving safety, and since 2022, all new stoves sold in the UK must be ecodesign-compliant. The UK Boiler Upgrade Scheme also offers grants under certain circumstances for biomass boilers (along with heat pumps), which in some circumstances are required, though grants are awarded in relation to fabric improvements as well as factors relating to location. These modern biomass boiler designs include pellet, woodchip as well as log burners that can provide hot water as well as heating needs, they also general have reduced pollution specifications as per the ecodesign compliant criteria.

The Ecodesign certification for stoves sets limits for emissions in five main areas:

Thermal efficiency, which is set at a minimum effective level of 75% net efficiency.
Carbon monoxide (CO) emissions in flue gases are caused by incomplete combustion during burning and were recently reduced by 90% from 1% to 0.12% content in the flue gas.
Particulate emissions, are heavily monitored in smoke control areas, and the newer ecodesign levels are now lower than some of the DEFRA-exemptt appliances, with around 80% improvements over older stoves.
Organic gaseous carbon compounds (OGC) emissions in flue gases are caused by incomplete combustion. The limit is120 mg/m33 at 13% oxygen; this is around a 70% improvement on older standard fires.
Nitrogen oxide (NOx) concentrations must be below 200 mg/m3at@ 13% oxygen on average from these stoves, which is actually a similar or slightly lower figure to older stoves.