Well, if you never get a chimney swept... Other than that, I can't imagine falling deposits ever causing a blockage. Mine's about the same width. It was relined when I had the stove installed. The real irritation was the bend just above the hearth. That meant they could only get a 6" liner in, so a 6" liner is what I have all the way up.

The next size up (8") would have meant I could have had a stove with a back boiler and, therefore, radiators... Mind you, I still haven't forgiven the Previous Owners. In a road of 12 30's built council houses, next door is the only one that still has the original fitted Aga. Not just heating! And yes, I can & do cook on the Canterbury stove (sort of). But, oh! For that original Aga!! Bloody vandals... :-/