Water stains around ceiling vent

Anyone know what causes water stains on a ceiling around the HVAC vent? The A/C wasn’t running at the time of the inspection. The stain was dry. In the attic, there is no other explanation for the stain other than from the HVAC duct. The flex duct seemed tightly sealed to the vent. No other vents in the house exhibit the problem.

Don’t know if the photo shows it well, but here it its.

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What kind of flex? Was the duct insulated?

May be warm attic air hitting the cold AC duct, condensing and running down to the ceiling.

Was it in a bathroom?

I vote with Larry.:slight_smile:

Yes. Very well insulated. House is 3 years old. The air getting to the duct is logical, but I didn’t see how it could have happened. Then again, I didn’t spend 30 minutes stooping down at the duct trying to figure it out.

Often this is cause by cold air escaping around the duct connection at the register. Typically you find it is being held together with just zip ties. cold air + warm moist attic air = condensation. Same thing you see around windows that leak air. Condensation on the window ledges.

I’m with Doug.

So what did you end up recommending??

I’m with Larry on this one.
Gee, I wonder why?

“A HVAC vent in the ceiling of the upstairs hall bathroom has a water stain around it. The A/C unit was not on during the inspection and the stain was dry. From inside the attic, the only logical source for the stain is from condensation around the HVAC duct. Repair to the duct by a state licensed HVAC contractor is recommended.”

The A/C unit was not on during the inspection and the stain was dry.???

I recently inspected a two year old fairly expensive home ($600k or so) and saw stains in the Master Bath separate commode room. I suspected the fart fan was not ducted to the outside and was drawing hot, moist air into the attic but it turned out to be something totally different. There were several large mice nests and burrows above the ceiling. Turns out to be mice urine! Talk about a freaked out Seller, she was even kind of annoyed at me, like I had brought the mice in or something. Anyway, I think the problem noted in this thread is condensation but I’d keep an open mind for other causes as well.

The condition is common around here. People run their air conditioners with a window or the sliding glass doors open. The warm moist air enters the home and goes upward, and condenses on the cold metal HVAC register.

The one above my recliner in my family room has “rained” on me from just that circumstance only to wake me up.:wink: Yes, there is a moisture stain around the duct.

I had this in a house I was staying in a few years ago. It was pretty rank. The house was in the country and essentially in the middle of a field, so the mice just treated it like their personal mansion.

They made nests in the attic, in the built ins, the shoes and drawers…

everything had those stains…


Not a good memory.:shock:

I am with Doug and Russel.

The only thing I would change with your report is ‘Recommend evaluation and repair by a licensed and insured HVAC technician’. I always leave the diagnosis to the pros. In that way, if there is some other problem or reason, I am clean.

Good catch.

I agree, Will.

That’s what I was thinking also…why I asked if it was a bathroom.

Showering, moist air up into the cold duct and water down to the edges and into the drywall.

Not to cause thread drift (after he did :smiley: ).

Don’t you find it funny?

Most houses I inspect have the bathroom exhaust fan switch separate from the light switch. I am told, by builders, that people like it that way. After about a year or so, the exhaust fan gets clogged up with shmutz (Jewish for all sorts of stuff) and the fan starts making noise. People don’t want to take showers with the fan making all sorts of noise so they leave the exhaust fan switched off. MAYBE they remember to switch it on after the shower when they are laving the bathroom.

Then they wonder how in the heck they keep getting mildew on the tiles, walls and ceiling and why that stupid looking vinyl bathroom wallpaper keeps peeling at the edges.

One of life’s little mysteries.

That is correct. What is unusual about my statement?