Thread: 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?

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Someone at my gas company had some tested a while back-- it's silicon. A build up typically indicates a venting issue.

This is basically the residue of particulate matter that gets burned in the flame and ultimately ends up being deposited near the flame source if it can not otherwise be carried away. What the resulting "ash" is actually made up of depends on what is in the environment being exposed to the flame or what fine particulate matter may be contained in the gas itself that is being burned.

Brandon mentioned silicon above and I have heard that high sulfur content in the gas is a prime culprit for such residue. I would imagine that any number of airborne materials and/or chemicals could leave behind this kind of residue after incineration in the open pilot or burner flame.

This deposition is usually more common around a standing pilot than on the main burners due to the low dynamic of airflow caused by the small pilot compared to the high airflow rate associated with an active burner assembly. Consider that the burned material around a standing pilot would likely precipitate out adjacent to (or be deposit above) the pilot flame while the "ash" off of the main burner would be more likely carried up and away to ultimately be ejected altogether out of the flue vent system.

If you happen across a vent system that is grossly oversized for the appliance you will often see these kinds of white deposits washing out at the vent pipe seams along with moisture from the flue gasses that are cooling too quickly to escape out of the vent piping.

Yup, Phillip hit it on the head. High sulfur gas often leaves behind the residue and will cloud your furnace flame sensor resulting in numerous attempts to ignite. As best I understand it, the residue covers the sensor and may be sanded off with a fine grit wire mesh to extend the functioning life.