Efficiency can be measured in two different ways: combustion efficiency and heat transfer efficiency. Combustion efficiency is a measure of how efficiently a fuel’s heat content is transferred into usable heat. Whilst heat transfer efficiency is the amount of heat that is actually released into your home from the appliance. So, in terms of which is more efficient, it will depend on several factors within your home, including the size of the area that requires heating, natural draughts and the level of insulation. Gas stoves tend to have better combustion efficiency as they are more air-tight and tend to have more insulation compared to a solid fuel unit and the vast majority of fuel is used in the burning process. Solid fuel appliances tend to have better heat transfer efficiency through a more complete burning process of the fuel and the ability for the appliance to get significantly hotter compared to a gas appliance whilst also being able to retain the heat for longer due to slower radiation. Which one should you go for? That depends on several factors, including personal preference and the area in the home which requires heating. Gas stoves tend to be more effective in smaller homes where only one room requires heating, whilst solid fuel appliances can heat a larger area and are more suited for rooms with extensions or areas where heat dissipation would be an advantage. In short, both gas and solid fuel appliances are both highly efficient heating solutions, neither of which is significantly more effective that the other, it only depends on the user’s requirements and fuel availability.

Absolutely! Gas stoves have a slightly different flue system to solid fuel appliances in that they can have either a conventional flue (one that uses the existing chimney and draws air from the room for combustion), or a balanced flue that does not require a chimney but draws air in directly from outside by way of a sealed pipe exiting through the wall behind the appliance. A balanced flue system is more suited for new build or passive houses where insulation is good, and air cannot be used from inside the building due to the air-tight structure and lack of natural draughts. Whereas a conventional flue is commonly used in older houses where the chimney stack can be used and there are more natural draughts due to the age and construction of the house.

Currently there is no regulation that requires that a pre-existing chimney be lined. However, the installer of any appliance must satisfy themselves that the chimney is suitable for the appliance and the fuel being used. In houses built prior to 1965 lining was less common. Flues were usually ‘parged’ (rendered) on the inside with a lime mortar. This parging suffers attack from acid and tars produced during combustion and as a result deteriorates over time. It is not uncommon for flues to leak fumes or tars into the walls or other parts of the house. For properties of and over this age the likelihood that lining will be required is good. In properties built since the introduction of the 1965 building regulations, all flues must be built with liners during their construction. This is usually done with clay or concrete liners, which should last the life of the building. However, many houses built since 1965 do suffer from chimney problems (examples detailed below) due to badly installed liners and would therefore need to be lined. There are a number of reasons why a chimney may need to be lined: • The chimney leaks smoke and fumes into other rooms or parts of the building • Condensates or tar are seeping through the chimney walls causing staining (This could be inside or outside the building) Most traditional chimneys are square however chimney brushes are round, therefore there are areas of the chimney that remain unswept. By lining a chimney using circular flexible liner you can ensure that when it is swept it is completely free of tars. • The manufacturer of the appliance specifies that the chimney be lined in the appliance installation instructions • The flue is much too large for the type of appliance that is being installed and would not draw properly • The flue is too cold and is not drawing properly (chimney on an outside wall) • The chimney was built after 1965 but was installed incorrectly (liners fitted upside down etc) • The old flue surface is eroded and rough, causing frictional resistance to the flow of gasses resulting in poor up draught. • If you have recently had your chimney swept and bits of mortar were brought down with soot this may be evidence of poor condition. A chimney can be pressure tested by sealing it off at the top and bottom and by using smoke pellets to test for leaks in the property (and where applicable adjoining properties). However, this can be a costly method, the costs of which would make up a proportion of the costs of lining the chimney anyway.