a perhaps silly airwash question?

It might just be some very fine fly ash on the glass rather than a problem with the airwash. Every so often we have to clean ours and that is all that is on the glass. I dampen a newspaper and dip that very gently on the ashes and wipe the glass with that. Works great as a glass cleaner. Or sometimes we'll also use some windex. Just part of the job of wood burning.

Glad you got the sweep.

I don't know about your insert, but both of my stoves have the air introduced above the door. It flows down the glass and then into the wood.

Yep. Air wash comes from the Top on the 30-NC. Would assume most stoves are like this. Are you talking about an EPA port at the bottom. Most stoves have other air inlets other than the Primary.

For example. The Englander 30 has a Primary intake (also the Air Wash), then Secondary burn tubes (no control over them - well you can, but really should not - modifying stove=void warranty) , then a little inlet at the very front (small hole directing air into the bottom front of stove at coal/wood level).

The little inlet at the front is fed by 2 small holes near the front of the stove (cant adjust) and the secondary is fed by a sqaure hole in the back of the stove (near primary intake)

I know the 30 is not the same stove, just letting you know that hole may be a small EPA intake. Or it could be the Primary for your stove, as I am unfamiliar with your model. But I doubt the air wash would be on the bottom. Both of my pellet stoves have the Air wash on top, although some models do have bottom fed air wash.

We all learn as we go.Keep em coming.

If we're talking about the airwash . . . as mentioned . . . most flow in from the top . . . you could simply be dealing with fly ash as mentioned by Dennis . . . if your wood is truly dry and you're burning at the proper temps, generally you can easily clean this with just a damp newspaper or rag . . . if there are some brown or black smudges from not burning hot enough, wood has fallen up against the glass impeding the air flow in that area or your wood is not as dry as you think you can either burn hotter and burn it off or use the damp newspaper with some fine ash to clean it. From the sounds of it I believe just a damp newspaper should work fine for you.