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 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 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 RegulationsThese are the mass of regulations that cover safety, health, welfare, convenience, energy efficiency etc. in the way buildings are constructed. Not to be confused with Planning consent (which is more to do with whether you can put up the building in the first place). See more on the 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.
Combustion appliances and fuel storage has a detailed section in the Approved DocumentsApproved documents (England) are detailed publications which come under the English Building Regulations. They are based on tried and tested methods of building and if you follow them you are assured of complying with the Regs. The equivalents for Scotland are the Technical HandbookUnder the Scottish Building Regulations, the Technical Handbook gives construction principles, which, if you follow them guarantee compliance with the Regulations, for Wales: the Approved documents (Wales), and for N.I. the Technical BookletsUnder the Northern Ireland Building Regulations, the Technical Booklets give construction principles, which, if you follow them guarantee compliance with the Regulations (part JThe Approved documents, (England) part J, deals with Combustion appliances and fuel storage systems) and this makes reference to several aspects of the design and construction of houses including:
- the construction of chimneys and flueblock chimneys along with wall thicknesses
- hearths, gathers, and bases for back boilers for gas fires
- fireplaces including large and unusual ones
- fluespipe to conduct gas, typically ventilation air or boiler exhaust. see more on Flues and their sizing including flues for gas appliances
- flue heights and how flue outlets relate to roof design and adjacent buildings
- ventilation and air supply for appliances (this has a large bearing on ventilation and air tightnessA measure of how leaky a building is to air. In other words, how draughty it might be. There are now standard fan pressure tests to check how air tight a house is and the Building Regulations have minimum standards for all new houses (L1A – Conservation of fuel and power in new dwellings (England)). A much higher degree of air tightness is covered by the Passivhaus standard generally).
- fire resistance[for the purposes of part B of the Approved Documents] - The ability of a component or construction of a building to satisfy, for a stated period of time, some or all of the appropriate criteria specified in the relevant part of BSBritish Standard 476. of construction close to an appliance
- the testing and repair of old chimneys
- storage of gas bottles and oil tanks
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.