Possibly the stupidest chimney is the one on the end of a traditional British house. It leaks most of its heat out through the wall and into the atmosphere.
If you have a chimney it should be on an internal wall[for the purposes of part C of the Approved Documents] - Any wall that does not have a separating function. or free standing 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 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 fluepipe to conduct gas, typically ventilation air or boiler exhaust. see 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 fluespipe to conduct gas, typically ventilation air or boiler exhaust. see more on Flues 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 RegulationsThese are the legal regulations which govern how a house is constructed. (not to be confused with Planning Permission which is about whether you are allowed to build the house at all or what it might look like) see 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.
The Building Regulations (part J) covers combustion appliances and fuel storage systems.
The width to height ratio of masonry chimneys needs considering and is stipulated in the Approved DocumentsThese are a part of the Building Regulations which ensure, if you follow them, that your plans will be automatically approved. The full set of the documents is available here – 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.