Chimney Fires

A chimney fire can reach temperatures of over 1000 ℃ and you will feel this heat coming through the brick wall. This extreme heat can cause serious structural damage to the chimney and surrounding walls and it can cause anything combustible that is near to the chimney to catch alight, quickly spreading the fire around the house. This includes furniture, ceilings, floorboards and joists and it can even spread to adjoining buildings.

If you experience anything like this, leave the property immediately and call the fire brigade.

Soot is created when all solid fuels are burned. Some fuels create more soot than others, generally burning ordinary house coal produces more soot than burning wood and smokeless coal. That said when any fuel burns inefficiently, more soot is produced.

When a fire is burning well with plenty of flames, most of the fuel is being completely burned away releasing energy in the form of heat. A slow burning or smoldering fire with little or no flames means that not all of the fuel is being burned away, some of it is turned into soot. Soot is carried up into the chimney by the up-draft created by the rising heat. It clings to the face of the brickwork inside the flue and quickly forms a thick layer. Soot itself is combustible and in large enough quantities can catch alight from sparks or burning debris that is carried up the flue.

Creosote is a by product of burning wood, particularly if the fire is burning inefficiently or the wood is ‘wet’ (un-seasoned) and it is commonly refereed to as ‘chimney tar’. All wood contains moisture and the more moisture in a piece of wood, the more inefficiently it will burn, releasing a lot less heat and a lot more moisture and creosote as hot gases. As these gases rise up into the flue reaching cooler brickwork, they condense onto the walls of the flue. Creosote mixes with soot inside the flue and can take a number of forms including a sticky tarry substance, a loose, dry crunchy material and/or a shiny glaze hardened to the wall.

All forms of creosote are highly combustible and they can be very difficult to remove, often sweeping is not enough and chemical treatments are needed. An experienced chimney sweep should be able to recognise the signs of creosote / tar and offer advise to help you to remove it.

• Have your chimney swept regularly. A large enough amount of creosote or soot in the chimney is the ideal environment for a chimney fire, so prevention is the best cure. East Sussex Fire Service recommend the following sweeping frequency based on the type of fuel used:
  • Smokeless fuels – at least once a year
  • Bitumous coal (ordinary house coal) – at least twice a year
  • Wood – quarterly when in use
  • Oil – once a year
  • Gas – once a year

  We recommend sweeping at least once a year before you start using your fire or stove. You know how often you have a fire so you should use common sense when sweeping. Always stay safe.
  

• Never use ‘wet wood’ in your fire or stove. The term wet wood actually means un-seasoned wood. All wood contains moisture and seasoning wood is the process of drying it out. As mentioned in the section Soot and Creosote, the more moisture in the wood you burn, the more creosote is produced.
  Some types of woods contain more moisture than others and they can take different amounts of time to season. We have listed different wood types and their suitability for burning on our Fuel and Appliance Performance page. Also don’t use wood that has been sat in the rain. Moisture on the outside is just as bad as moisture on the inside.
• Lining your flue can make it narrower which should increase the draw speed helping smoke and emissions to leave the flue quickly rather than staying inside and condensing onto the flue walls. If your chimney is on the outside wall of your house it can be a lot cooler again causing gases to condense quicker. Insulating and lining your flue will again help to reduce condensation inside the flue.
• Avoid overnight burning or smoldering wood for long periods. Fires and stoves that are said to be ‘slumbering’, i.e. they burn very slowly to keep them alight for a long period of time, produce a lot more soot and creosote than during normal use. Instead of the fuel being converted to energy in the form of heat, it is converted to soot and gases that in turn condense inside the flue.
• Use a stove thermometer with wood burning stoves and multi-fuel burning stoves to check the stove is burning at it’s optimum temperature for heat generation. Use the stoves air intake vents to manage the amount of air entering the stove to maintain constant flames that fill the firebox, ensuring wood is burnt properly and reducing the amount of soot and creosote being produced.