Rust/water collecting on top of water heater

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IGx89

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Hello! I have a 7-year-old AO Smith gas water heater (GCRL-40 400). About a year ago I started seeing minor rust/corrosion appearing by the flue, and it's progressively gotten worse to the point where so much water collects on top that it drips to the floor. When I research on Google everything points to backdrafting, but when I put my hand up to the flue it's never hot and smoke from a match seems to be easily pulled up. I have a 6in combustion air intake within 10 feet that's unblocked, and this seems to still happen even if every fan in the house (furnace fan included) is off. It's dry when we come back from a vacation, so it's not a pipe leak.

The vent is horizontal for ~12ft and then goes straight up ~25ft, sticking up ~5ft from roof and capped with a Dura-Vent cap.

Any ideas what could be the cause? I know a new power vent water heater would solve it, but would like to only go that route as a last resort. Any chance it could be an issue with the water heater itself that could be fixed by simply replacing it? Seems really odd it worked fine for 6 years before having this issue. Nothing's changed with the furnace in 10+ years.

Thanks for your time!

-Matthew
 

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Fitter30

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What are your two flue sizes ? The red and blue plastic gromlets if their deformed it's from back drafting and the flue should be hot to the touch. How far is the flue cap from the peak and does it stick over the peak? Furnace hasn't changed in ten years but the trees have.
 

IGx89

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4in and then 6in. I could have worded it better: the flue itself is very hot when touched, but if I hold my hand up to the air gap under the vent hood, to check if exhaust is going into the room vs. up the vent, it's cool.

Good point about trees! It's below the roof peak but I believe is at least 8ft horizontally away from the roof, which I've read is the requirement if below roof peak. No trees to the west. Unsure if the vent is single walled or double walled -- it's single on the horizontal stretch at least. Built in 1984.
 

John Gayewski

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Do you have a supply of wet air your water heater may be using to light the flame. It could be your combustion air needs to be dryer. Had your basement been leaking or did a dehumidifier get taken out of commission?
 

IGx89

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No leaking, walls painted with Drylock Extreme four year ago. I have dehumidifer in a corner set at 50% and a water sensor at the bottom of the water heater that reports 58% humidity. It's been a lot more humid in the past (70%+) before this issue started.
 

Fitter30

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4in and then 6in. I could have worded it better: the flue itself is very hot when touched, but if I hold my hand up to the air gap under the vent hood, to check if exhaust is going into the room vs. up the vent, it's cool.

Good point about trees! It's below the roof peak but I believe is at least 8ft horizontally away from the roof, which I've read is the requirement if below roof peak. No trees to the west. Unsure if the vent is single walled or double walled -- it's single on the horizontal stretch at least. Built in 1984.
A chimmey sweep or hvac company could help u out. Might take a flue liner and raise the the flue over the peak. New heater might be cheaper.
 

WorthFlorida

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It all looks like condensation dripping down the flute before it gets hot enough to start a draft. It's surface rust in my opinion.
 

IGx89

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Update: water collection on top kept increasing, dripping onto floor more and more. Problem ended up being the water heater itself, it apparently had a leak somewhere in the tank at the top. Have a brand new water heater now (Bradford White), installed five months ago, and the top’s been clean and dry since. Went from a 40gal short to a 50gal tall too, and the family’s appreciative that we can have a bath and shower at the same time now without running out of hot water :)
 
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