Thread: White "powder" at furnace exhaust tube

Question for those HVAC experts (pardon my poor terminology). 1950's Coleman gas forced air furnace. I noted some powdery white substance both on the bottom floor of the furnace (below the burners), and specifically I saw a lot of very white powdery coating on one of the heat exchanger exhaust tubes (just below the draft hood). The flame pattern and color of the burners all looked about normal for this age of a furnace (I did not witness the ignition). I saw no readily visible cracks. And remember, only one of the four exhaust ports had this white substance. I am of course referring the client to a HVAC pro, but wondering if someone has an ideal if this is an indication of poor combustion and too much condensation in that particular burning chamber, or is this an indication of a crack in the heat exchanger?

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