I have been noticing a thin layer of brown ash starting to build up on my stove walls above the fire bricks. And when i look up over the baffle board/ blanket as well. Is this something to be concerned about? I also noticed it when I pulled the bottom of the clean out T off to look up the chimney there was a little on the pipe walls. The stuff just brushes right of with the broom. If its preventable what do I do different to prevent it? Or is it just a by product of burning? And just keep an eye on it?