Its the secondary heat exchanger. I am on at least the 3 year plan.
All fuel is below 20*/. Moisture.
I should probably slow my blower down.
My yukon is a newer one with stainless secondary exchanger.
26 feet of class a chimney.
No it doesnt plug that bad but i look at it once a month or so. Its really easy to do and i can open it up and look and have it back together in 10 minutes.
20 if i decide to scrape the tubes and run the shop vac down them.
I have never needed to clean the flue in over 10 years. Theres nothing there.