I'm having some issues with my Napoleon NZ3000 ZC fireplace as well (it's alot like the Quad 7100). I know for a fact that my wood is dry and seasoned (seasoned three years, top covered since early summer), same wood burns fine in my Napoleon 1900p with no black glass at all, even on a slow, lazy burn. I try that same, lazy burn in the NZ 3000 and the glass gets black, every single time.....no creosote in the chimney or on the chimney cap, just black glass. I am thinking that my doors need adjusted as they seem to be sucking some air in (right in the middle where the doors meet), when they suck air in around the doors that nullifies the air wash for the glass (the air wash is a bunch of little holes at the top of the door where draft air comes into the stove, and washes down over the glass), that air is supposed to move over the glass which in turn doesn't allow any condensation on the glass, which in turn means clean glass. Anyway, look and see if your doors are sealing tightly. Do the 'dollar bill' test (take a dollar bill, close it in the door gasket. If it stays in tight, your gasket is tight. If it pulls out easily, your gasket isn't tight enough). you may be having the same issue that I am.......leaking door gaskets and not enough air wash coming down across the glass to prevent condensation.