Damaged chimney within the ruins of a fire. It is possible that this is the remains of a smoke hood, a wood, wattle and daub construction that pre-dated brick chimneys, incorporated within the newer brick and stone stack.		Multifuel and Woodburning Stoves
		Research undertaken in the 1990s, by a number of industry and government backed projects, changed the traditional perception that thatch fires were mainly caused by burning material falling onto the roof. Their findings moved the greatest area of concern from the surface of the roof to the interior of the chimney. This is particularly relevant when we consider the advent of multifuel and woodburning stoves. The increased heating efficiency of such stoves, whilst very welcome to residents of otherwise draughty older properties, has its own implications with regard to fire risk. Such efficiency depends on a high flue box temperature of around 500°C which is achieved by restricting the airflow. Installed in a properly regulated, modern chimney it is a highly effective way of getting maximum heat out of burning wood; but where ancient chimney stacks are concerned, the inappropriate introduction of such installations can create serious problems. Research carried out by RHM Technology indicates that in a single-skinned brick chimney, heat can migrate into the deep thatch surrounding the stack and needs only to reach 200°C for charring of the thatch in contact to commence. And while this may not happen immediately, it must be remembered that the process of lighting and extinguishing the stove takes place on a regular basis year in, year out. If the use of such stoves is to be contemplated in an old thatched house, it is essential that a liner be inserted to isolate the hot gases from the surrounding brickwork. It is also essential that such lining is carried out by a properly qualified installer to ensure that it runs centrally without coming into contact with the chimney interior, that there are no gaps in concrete segment liners and that it runs the entire length of the stack. The most popular of liners is of a double skin metal construction, but whether this type or pre-formed concrete sleeving is used, the void around the pipe work must be backfilled with the recommended insulation material to avoid intense heat bridging the gap.

View down the remaining part of the chimney following a thatched property fire in Essex. The central chimney provided the outlet for a woodburning stove. The lining material does not fully surround the cement liner, allowing heat to transfer through the single skin chimney stack into the thatch.

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