I have a Napoleon Pellet Stove that has a dirty window issue. The upper half of the 3 windows get covered with black stuff that wipes right off. I have a log set. Normally run the stove on 4 with a fan speed of 2. Nice stove, really good heat, but not able to get support from Napoleon. Their reply was to get the technician to inspect his installation and give them a call. I had this technician do the installation. Considering he cut two holes in my siding before connecting to the one inside hole, I don't have a lot of faith in that option.