Went on an estimate and saw this. He said he had just bought the house 5 years ago and it came with the new water heater. I didn't have furnace cement on my truck but I did explain the severity of this to the homeowner. In the meantime I tagged the heater and furnace gas lines and shut them off. I offered to come back with the furnace cement and seal it for him but he said he has a guy.
Keep in mind this about 6' from the door leading into his kids playroom!