Inspected a furnace today. Looks like there has been some flame roll out that even singed the duct work. This furnace was in the attic, obviously there wasn’t enough clearance from combustibles as I found the deck right up next to the front of louvers. Would a cracked heat exchanger cause a back draft from the flue causing a flame roll out? This was a mock inspect, I’m just trying to get some understanding as to what might have lead to this. The draft diverter was pretty rusted as well. Thanks.