What might have caused this?

[Robert Jones]

The installed gas furnace is approximately 13 yrs old. There is quite a bit of "mineralization" on the b vent and the burner compartment. Is this caused by poor drafting? The flue is shared with the water heater.

Thanks

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[John Dirks Jr]

It looks like the gasses are condensing in the flue which leaves behind the acidic corrosive minerals you see. It could be a number of things causing it.

So yes, it is a drafting problem.

[hausdok]

Yep,

Draft issue. That's a 90° elbow in a single-walled vent in an unheated garage. Those gases are slowing down and cooling too rapidly and condensing in that vent.

What's the rule?

No bend greater than 45° but one bend of 60° is allowed - isn't it?

ONE TEAM - ONE FIGHT!!!

Mike.

[Robert Jones]

Thanks guys.

Mike, that is correct, per IRC 2426.6.4, bends 45 degree max. except one of 60 degree.

Thanks again.

[Chad Fabry]

It looks like the gasses are condensing in the flue which leaves behind the acidic corrosive minerals you see. It could be a number of things causing it

Is the residue acidic or did acidic condensate degrade a component of the flue material?

[Kyle Kubs]

Robert, just to enforce proper nomenclature. That is not a "B" vent. A B vent is a listed, double walled pipe.

You probably already knew that, but if I don't post more, I'm going to be a two star member forever....[:-dunce]

[Robert Jones]

Sometimes I don't think before I type on this board and I really should. Nothing get's by anyone;)

[John Dirks Jr]

It looks like the gasses are condensing in the flue which leaves behind the acidic corrosive minerals you see. It could be a number of things causing it

Is the residue acidic or did acidic condensate degrade a component of the flue material?

Acidic condensate caused degradation. Correct?