Need Ideas Why Water Dripping from Ceiling Vent in Winter

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Old 12-10-18, 01:58 PM
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Need Ideas Why Water Dripping from Ceiling Vent in Winter

I have a square ceiling vent in a bedroom that drips water maybe once per 5 minutes and:

1.) It's the middle of winter and the high is 35 degrees F.
2.) It's an A/C only system, not a heat pump;
3.) It hasn't rained for over 10 days;
4.) The attic just above has blown-in insulation and the flex duct is insulated;
5.) There are no water pipes in the attic;
6.) There is no condensation sheen on the ceiling vent, just one spot that drips;

Does anyone have any ideas on something I can do? ...like tape some plastic over the vent to see if it's condensation vs. dripping through. I'll be looking at it tomorrow in the attic a second time; the 1st time, I could find no stains and no water under the attic insulation.

Thanks!
-TonyT
 
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Old 12-10-18, 02:10 PM
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Take the grille off and reach your hand in there. It's probably condensation from warm air in the house coming into contact with cold air in the attic. I bet you have a puddle that has collected inside the ductwork and what's dripping is because the puddle is running over.
 
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Old 12-11-18, 01:11 PM
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Xsleeper, thanks for your reply; I did look at it today and went into the attic.

When I removed the grille, there was indeed moisture inside the insulated flex duct where it turned from vertical to horizontal; you were right.

So, what is the fix? Put some bat insulation over the flex duct in the attic? Or put a cover over the vent? The dripping occurs even when the vent is fully closed.

FYI: I found a ton of moisture in the attic but how would it ever make its way into a closed system of insulated flex duct --> Air Handler --> Central Return? Unless it's just a coincidence. I'll be venting the shower and dryer vents to the outside this week.

Thank you.
 
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Old 12-11-18, 04:40 PM
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I assume it's condensation... humid air from inside the house condensing on the inside of a cold duct. The solution in in my opinion is that all ductwork needs to be positioned as low as possible.... then covered with a ton of blow in insulation. R-49.

If fresh air from outside is somehow washing down this ductwork, that would be bad. So all the seams in the ducts need to be taped and air sealed.
 
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Old 12-12-18, 12:43 PM
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I have wrapped the offending flex duct (only one vent is dripping) with R19 batts for about 6 feet today. I'll wait and see if it stopped. It's not dripped for the past 10 years, so I'm thinking crazy perfect conditions may have pushed the condensation point just barely over the edge and that the insulation MAY protect against those rare conditions.

If it continues to drip, I will try a cover for the 12"x12" vent, stopping room air from migrating into the cold attic flex duct. I found a product called AC Draftshield which is made for this exact thing.

If it STILL drips, then I'll have to install a thermostat that turns the circulation fan on randomly during each day. I don't know much about them, so I'd have to look more into that.
 
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