maybe you guys can help me out: my brother-in-law has a vermont castings gas (propane) fireplace insert. he's had it for five years without a problem. this year the glass is turning black on him. the outfit that installed it isn't being much help. they claim it's not getting enough air, although the conditions haven't changed any. then they said it's probably the propane. sounds to me like they're not much interested in helping him out. any ideas as to what would be causing this condition? thanks for your help in advance.......tonyg