There is a lot of nonsense on the internet about liners, most people think it’s a necessity or a legal requirement, but it is not. The fact is, if your chimney is working you don’t need a liner, we only fit them in about 1 in 20 jobs, you’re putting a fire in a chimney which has been built to have a fire. If your chimney isn’t working properly, it can be fixed most of the time by pointing up the chimney, it is usually a bit of loose pointing that needs redoing! A small hole can cause the chimney to fail. Chimneys work on the principle that warm air rises and cold air drops, if your chimney has the smallest hole in it the cold air will be drawn in, the smoke will cool and drop back down, you will then know instantly that the chimney is not working, smoke will be coming out through the stove. All chimneys built from 1964 have a pot liner inside (building regs) and work very well, in fact I haven’t come across one that doesn’t work in 44 years of fitting fireplaces, unless there are other problems. Generally, much older chimney’s also work very well.
Some retailers genuinely believe you need a liner; however, there are retailers who want to make a bigger sale by telling you it’s safer, more efficient or a legal requirement, the truth is, it doesn’t make the fire safer and only makes it marginally more efficient, if at all. Smoke is not as dangerous as many people think, you can see it and smell it whereas in a gas fire if you had a carbon monoxide leak you would not be able to smell or see it.
– William Evans