Picked the 12-inch brush over the 10-inch for a tight clay flue in Rochester and it paid off
Two sweeps on the crew said the 10 would fit better in those old clay liners, but the 12 got full wall contact on the first pass and we cut a good 20 minutes off that job.
Used to be in the 10-inch camp for years. Kept thinking the smaller brush would move easier in those old liners, and I'd get less drag on the rods. But then I tried a 12 on a job like yours and it was night and day with the wall contact. Cutting 20 minutes is no joke either, that adds up over a week. Guess we all get set in our ways and it's the job that teaches us.