Hi,

Soot buildup could be much more of a problem with unlined chimneys.

So for professional installers, lined insulated chimneys have much
more butt covering potential in case the chimney gets neglected.

Once a chimney fire gets going I wonder if it's easier to stop with a
stove rather than an open fire.

Maybe worth getting the opinion of an experienced chimney sweep, who
may favour something that needs more sweeping, but could have some
good advice.

cheers,
Pete.