Scorched water heater

[Mark P]

First time I've ever come across this. A.O Smith water heater manufactured in 2003, same year as the house was built. The vent pipe is not shared with anything else. The draft hood is well attached. Nothing else seemed wonky.

I'm looking for your thoughts...

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[Marc]

What's the vertical height of the flue?

It may have been due to conditions no longer present like a flue too short. The flue pipe in the photo looks new.

Marc

[Mark P]

I don't know the height. The vent goes up at a 45 degree angel for 6+ feet then goes straight up and terminates above the one story garage.

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[mlparham]

Does the homeowner park in the garage everyday? If so I would back drafting when the garage door is opened. If the homeowner does not park in the garage I would still back drafting.

[Mark P]

IDK - The home is vacant. This is what I put in the report, but I have not sent it out yet, so it may change.

FYI: The water line connections to the water heater are scorched. This was caused by hot exhaust gasses spilling out from under the draft hood. I found no problems with the vent pipe. I can only assume that the condition that existed for the scorching to occur, no longer exist. Ask the seller if they know anything about this.

[Mike Lamb]

I would skip the assumption about no longer back drafting. An HVAC guy needs to consider.

[David Meiland]

I agree, skip the assumption about no longer backdrafting. It looks like there was a huge amount of exhaust gas spillage, possibly because of a negative pressure situation in the garage, or perhaps a dead squirrel blocking the vent pipe. It could still happen sometimes, and needs to be ruled out by not you.

[Jim Katen]

Does your local code allow single-wall vent connectors in unheated garages? Mine prohibits it. Could be relevant.

[Mark P]

Thanks for the comments. The water heater is in the unfinished basement, not the garage. The exhaust vent passes through the garage attic. I'll pass the ball to a HVAC guy to evaluate the venting details.

[Steven Hockstein]

Maybe the vent run is too long and there is moisture condensing in the vent pipe AND there is back-drafting. This may result in moist fumes blowing onto the fitting and causing the corrosion

Additionally, there seems to be additional corrosion caused by dissimilar metals at the fitting.

[Hearthman]

A pro certified in CO/combustion analysis should test and correct as needed. The vent connector should rise straight up as far as possible while still making room for the 1/4" per LF slope up to the vent. The vent connector should be supported at the offset and every four feet. The vent should be inspected for obstruction (level II). There could be a a flow obstruction such as damaged inner liner or the use of TEK screws pushing in the inner liner instead of piercing it and pulling the two single walls together. If the B-vent joints have any screws, this is a common defect. A worst case depressurization test should be conducted.

There is either a flow obstruction or a depressurization issue WRT the CAZ. This is just another reason to remove draft hoods--they work just as designed. They are the most dangerous item in a home. An NCI pro knows how to make the repair to a bullhead tee with double acting barometric damper and spill switch. Backdraft must always be investigated and corrected or somebody could wake up dead.

[Marc]

...or somebody could wake up dead.

Is that how them zombie's are created?

I wonder if the backdraft is confined to the winter season when the entire length of the flue is subjected to cold winter temperatures? These are Illinois winters and not an inch of the flue runs through conditioned space.

Marc

[Tom Raymond]

Basements are conditioned. On purpose or by duct leakage or jacket loss.

[kurt]

This can't be complicated. Flues draft and work when installed correctly and they're not blocked. That much corrosion means something was/is wrong for a while.

Agreed on the punt. It shouldn't be hard for someone to figure it out.