Excerpts from Specialist Flue Service's article on Chimneys & Fires

Thatch Chimneys & Fires

"If you have a fire or stove, which is in constant use throughout the winter then your chimney should be cleaned at least every three months, and checked at monthly intervals.

When burning wet or resinous wood, the tars and creosotes produced will deposit on the chimney wall and build up, eventually blocking the chimney. Attempts to sweep this away will be unsuccessful as the brush will only slide over the surface.

I recommend a product which, added to the burning fire releases chemicals in to the flue gas, loosens the adhesion properties of the tar, and allows it to be swept clean.

A dirty chimney, covered in soot or tar, is an incinerator waiting to be ignited.  When the fire or stove has been stoked up, a long flame path is created, into the lower section of the chimney.  The deposits catch fire, then race up the surface of the inner chimney wall. In these circumstances temperatures can rapidly escalate and reach as high as 800º to 1000º C.

At these temperatures bricks crack and mortar joints crack and open up, allowing heat to escape and contact wood or straw adjacent to the outer face of the chimney.

The tars are deposited when damp wood is burned, especially when the stove is run for long periods at low fire. The ignition temperature of the gases ejected from the wood is higher than the fire combustion temperature and they travel into the chimney to cool and turn to liquid and then solid deposits.

Ideally, wood should have a moisture content of less than 25% before it is used. This can only be achieved by careful husbandry of the log store. Do not use the logs until they show splits in the end of the log - then it is ready for the fire.

Many fires occur during the latter months of the winter heating season. The longer the cold weather continues into spring, the greater the number of fires we see. This can be due to chimneys getting dirtier with the extended use.

Chimney Data

(Not exclusively thatch but very interesting and worth taking no)

UK Figures 1999/00  Dwelling Fires = 69547: Chimney fires = 16209 = 23.30%
Eng Figures 2000/1   Dwelling Fires = 54933: Chimney fires =   9122 = 16.60%
UK Figures 2009/10  Dwelling Fires = 48849: Chimney fires = 12319 =  25.21%
Eng Figures 2009/10 Dwelling Fires = 38584: Chimney fires =   8145 =  21.10%
Eng Figures 2010/11 Dwelling Fires = 36339  Chimney fires =  7630  = 21.00 %

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