Well, we put the Monty in three seasons ago. It works great! Well this year I finally decided to get the installer out to clean the liner! They show up and the first thing the did is cover the floors with drop cloths. They then cleaned the pipe got about 1/2 gallon of crumblies out of the liner. They said it was the good kind. No real problems found. They inspected the door seals and cleaned the whole unit. Well worth the money as I have at least 20 feet of chimney and a roof you cannot walk. A very professional job. They thought I could go 1.5 years before the next cleaning. Don't think so, I'll have them back next fall. I think most of the crud was from the first year. Very happy camper here.