Crystal formation in combustion chamber

Crystal formation in combustion chamber Quite often while inspecting furnaces, I notice a white substance in or around the area where the burners are exposed. Sometimes this is a powdery substance and other times it is more of a crystal formation. I am not sure if they are related causes but suspect it is due to improper gas and or air ratio. I would like to be able to give a more professional and knowledgeable remark in my reporting. Are there any suggestions and or are there sites one can get more information pertaining to HVAC systems?

Mineral deposits from condensation (sometimes evidence of poor venting, and/or incomplete combustion), left after the water evaporates when the gases are not staying hot enough to escape the vent pipe.

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Yep, see that a lot when furnace is replaced with a high efficiency and the six inch flue designed for both furnace and water heater is now only being used for water heater.