Although not a regulation, I always advise clients that are planning to have a stove fitted to also line the chimney’s existing 9″ brick flue with a stainless steel lining system. (these are either 5″ or 6″ to match the stoves pipe) This is because stoves lose much less heat up the flue than open fires, this creates a colder and slower draw giving hot gases meeting colder air time to condense and stick to the flues walls.
With the liner being smaller in diameter than the original brick flue, gases are expelled quicker as the steel liner conducts heat. This creates a faster draw tackling the problem of gases having time to condense creating tar and creosote build up. Creosote can eventually leak through causing damp tar stains. It is also very flammable and the main cause of chimney fires. The image slide shows a heavily saturated brick flue.
A liner also creates a much more efficient stove on fuel. The liner is dropped from the roof and connected directly to the stoves flue pipe, creating a safe installation preventing smoke spillage escaping through leaking mid feather bricks into bedrooms above. This is a very common problem on houses built before the 1960s.
Another benefit of having the stove lined is it makes the sweeping process much cleaner, easier and quicker. This keeps your hearth and the walls of your chamber free from any soot as there is no need for sweeping hatches in the closure plate. The liner is swept through the stove as it is now all one connected system.
There is two types of liner available, the difference is the grade of steel used, a 316 grade liner is suitable for mainly wood burning and a 904 grade liner for a mixture of wood and coal. 316 grade liners usually have a guaranteed lifespan of at least 10 years while a 904 with its higher grade steel usually 20 years. This will vary with different manufacturers. Some clients still prefer a 904 grade liner even if they only plan to burn wood, this is down to its longer life span. However if incorrect fuels are burnt the lifespan of your flue liner will be reduced significantly.
Like any working chimney flue liners need sweeping at least once a year, this stops any buildup of soot and creosote and keeps the liner smooth for expelling gases.