Sandy substance at collar of flue?

[greyboy39]

Saw this sandy substance at the bottom of a mechanical draft flue today any ideas? Could this be a byproduct of backdrafting?

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[Brandon Whitmore]

Did you see signs of flue gases condensing anywhere, such as white chalky type substance @ any joints/seams. That, or was the furnace older than the venting system?

If you did not, try tapping on the vent several times to see if anything starts to drop out at that area above this induced draft furnace next time.

Sorry, but this close up shot isn't much to go on- that could by anything.

PS: Did you taste or feel it, or perhaps rub some in your eye to see if it burned?[:-monkeyd Just figured I'd beat Katen to these questions.

[John Kogel]

Right, it looks like somebody spilled chicken feed there.