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interesting bit of chimney building!

Very stupid

Possibly the stupidest chimney is the one on the end of a traditional British house serving an open fire. It leaks most of its heat out through the chimney pot, the external wall and into the atmosphere.

If you have a chimney it should be on an internal wall or free standing internally so that any heat escaping through the sides goes into the house rather than warming the sparrows. If it is on an external wall then there is a strong case for external insulation to that wall.

The traditional Northern European solution was the Kakkelovn (or Kakelofn) which is an extremely efficient stove usually used for burning timber. The stove is charged with timber and then allowed to burn fiercely for about an hour. This produces a very clean burn with little ash. The heat is absorbed into the mass of the stove and the chimney via internal flue ways. The heat is slowly released over the next 24 hours or so, partly by means of ventilation and partly by means of separate ducts which carry warm air into adjacent rooms. A large chimney mass is important to absorb the heat from the burn and then to hold it for a long period.

Existing chimneys may need relining if they are brought back into use. It rather depends on how old they are. With the introduction of the 1965 Building Regulations it became mandatory to line chimneys and this was usually done with vitreous clay pipes which have a good life time. However, up to that date it was common to simply parge the inside of the chimney brickwork with a render. The parging tends to break down with acid attack from coal and produce the bits of mortar that you often find at the bottom of chimneys in older houses. After the parging has gone the brickwork and mortar get attacked and begin to leak smoke. It is therefore important to check out the condition of older chimneys and reline them if necessary. This is usually done with a flexible steel liner lowered down from the top and then insulated if necessary with mineral fibre or pumice. There are various companies which specialise in this. Existing chimneys which are situated on external walls particularly benefit from external wall insulation.

Building regulations

The width to height ratio of masonry chimneys needs considering and is stipulated in the Approved Documentspart A.

HETAS is the official body recognised by Government to approve solid fuel domestic heating appliances, fuels and services including the registration of competent installers and servicing businesses.

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