Creosote buildup in the upper third of the flue
Why it happens here
Mount Cook's cool, windy draw cools the flue gas quickly, so creosote condenses on the upper liner rather than burning off. Heritage clay liners make it worse because they stay cold longer.
Our approach
We brush the full flue with polypropylene rods and check the upper third with an inspection camera. If the creosote is glazed, we treat it chemically first, then sweep, so the deposit actually comes off rather than smearing.