Log burning stove seals

[Hotrodder]

I think liners (at least insulated ones) are supposed to be less prone to deposits and easier to keep clean - so less of a fire risk. And also prevent creosote from soaking through the brickwork. So worth persevering.

Maybe if you cannot get an insulated one to fit try an uninsulated one as they are more flexible - then fill the chimney void with vermiculite insulation?

Insulated would certainly be the best but hugely more expensive. My chimney is not brick but old random stone construction with lots of internal pointy stones so flexible is a must. I discovered (through extensive research) that the flexible ones need to be installed the right way up. Looking at a cut cross section of the liner wall, one way up directs fluids through it to the outside (hence the potential for staining) and the other way up keeps any fluids inside the flue. Not always obvious which is which.

[L Austin France]

Our woodburner has been a bit of a swine from day one. After about 6 years of aggro we are trying again to get a flue liner in place. The installation manual says the flue should be 200mm diameter to fit the output spigot on top. An expensive 200mm flue wouldn't fit down the chimney and was destroyed in the process of trying.
This time I have fitted a reducer down to 180mm hoping that will fit. At the moment the glass soots up in two or three hours until there is only a dinner plate sized clear bit in the middle. And when it rains hard for any length of time the water pours down the chimney and even behind the cement render on the wall. We spent a fortune this summer getting the chimney repointed and flashing around it replaced. Every time the bod climbs up there to do any work more slates get broken because the roof is years overdue for replacement.

I'm told having a liner should make the fire start easier and be more controllable. I am starting to wonder if it is worth all the bother to get it right.

Without knowing exact details of your woodie/house I'm assuming a 10/12 kw output & chimney height from top of fire of about 5m.
From this, based on my experience with two woodies in my house, I'd say that a 180mm liner would be adequate. I've got a 10 kw fire running on a 10 m high 150mm liner & 7 kw running on 5m high 150mm. Both work fine although the shorter mostly freestanding flue sometimes needs a 'kick start' with a 'petrol' soaked piece of kitchen roll, when very cold to get the 'draft' going in the right direction.
It seems to me that your current problems are probably due to a cold & damp existing ,presumably stone built, stack which will not 'pull' until hot enough to create sufficient buoyancy. A liner, sealed top & bottom, will overcome most problems but if the chimney is on a 'cold', gable you may still initially suffer from reverse air flow until the liner is warmed up . My kick starting trick will sort this.
You probably know this but the 'upside down' fire lighting technique where kindling is lit on top of a few logs works well in getting plenty of heat into the chimney without much smoke.
Fit the liner & cowl. You'll not regret it & much safer & easier to sweep.