You really need to burn dry wood and burn it hot, our flue had virtually nothing in it when we had it swept, but we always let it burn hot and burn out each night. It’s used every day from about October until March.
My other half used to build the fire up then shut the air supply down so it’d stay in all night, that was not good, since we changed how we use it, it’s much better, glass never needs cleaning, ropes are all still perfect, after 3 years.
In the market town I work in the air is noticeably acrid in cold weather due to coal and wood fires, stinks. I don’t really think they’re the ticket in town tbh.
I also can’t see how they’re sensible financially if you have to buy wood. What we’re burning is generally a lot of windfall/powerline felling left overs, and all off the farm. Most actually comes from within a couple of hundred yards of the house off the old railway line.