I just came out of an old boiler room, which has a ULN100-199 AS American Standard power vent gas water heater of 100 US gallons. Shortly after it fired, water started to rain down from the wall behind the heater, and there’s plenty of evidence of rust. The water droplets are completely clear. The dripping appears correlated with the water heater firing.
The water heater was installed in 2019, and the anode rod has never been replaced.
The flue is damaged, corroded in the top image. Damage has been on going for some time. The opening would allowing water to enter the chimney/chase.
Ad to that, flue gas condensate is a produced liquid, where appliance flue gas is cooled below its water dew point and the heat released by the resulting condensation of water.
Refer to a licensed flue liner installation and service repair contractor for further review and flue replacement.
That could turn around to bite you hard. Diagnosis: investigation or analysis of the cause or nature of a condition, situation, or problem.
So explain how you came up with the flue is too wide as opposed to other conditions that can cause the same outcome. Full readings, measurements and equipment used and what the water heater manufacture recommends will do
I have all the tools, recognized, brand name, and required calibrations when required, and don’t go there unless it’s a specific ancillary inspection. You put your credibility on the table, which might be presenting said findings and calculations in a court of law.
Look at where the flue enters the foundation. I see brown streaking stains. Then look at the chimney crown where the flue exits the chimney and describe what you see.
There is only one thing you can comment on w/o getting into a potential problem; Condensation.
There are only three sources of water leakage: Holes in the building envelope, leaking plumbing (supply/drain), condensation.
You need to collect the right information if you want to report more.
Condensation needs moisture. As you said, combustion exhaust has significant moisture. Is the leak source from interior or exterior of the flue?
Removal of heat from that moisture. What is the ambient temperature? And what is the Dew Point temperature of the ambient air? So what was the temperature at the time of your inspection. The ocean water at your location is cold year round (likely source).
Report all Visual Observations. Photograph.
It’s not your job to figure out the cause, just the problem that is occurring. It is your job to collect and report proper information (not about if the anode was ever changed or the date of installation). These things can cause condensation in the winter, regardless of age. And some of this condensation is common and not an issue. In this case, it is a significant issue.
Everything else is to be determined by who comes after you.
The path forward is “Here is the defect, here are my safety concerns and here is my recommendation”.
Consider this. The flue is replaced with a smaller one and the condition returns. Maybe there was a problem with the burner of the water heater or make-up air, negative pressure or back-draft causing the gases not to rise efficiently. Fingers will certainly be pointed back at you. You may be correct in your diagnoses, but you needlessly boxed yourself in.