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Old 06-17-2011, 03:48 PM   #1
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condensation drips from supply vents

Hey all,

Recently finished my basement. Added a supply vent to a room which happens have the door to the outside. The vent is on the opposite wall, so about 12 feet from the door, and the vent is on the wall 7 feet up.

Whenever we have parties or need to leave the backdoor open for some extended period - condensation forms on the vent. Then it drips down the wall. It's just water - but it leaves marks that are easy to see.

There is another vent in the ceiling of a room even closer to the door - but pressure out that vent it less as the duct run is much longer and a gauge smaller. Haven't seen water there.

We live in Atlanta. We're not going to shut of the AC. Unfortunately - at times when the door would be open - we'd probably need the AC even more.

If it's forming on the vent - I wonder if water is forming inside the duct too.

Any fix here? I thought about putting a foam block/sponge just under the vent. I figured by the time it filled, we'd have the door shut and I wouldn't need to do anything - just let it dry out.

Thoughts or ideas?


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Old 06-17-2011, 04:29 PM   #2
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Ever seen a glass of Iced tea, or Pop can sweet. Your vent is doing the same thing, due to Dew Point.


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Old 06-17-2011, 04:47 PM   #3
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Gotcha - I know it's natural, but still undesireable . I guess you can't control mother nature - just wondering if anyone has rigged up something to deal with it...

Maybe I need to paint a waterfall scene just under it.
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Old 06-17-2011, 04:59 PM   #4
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Friends renovated a gorgeous old opera house last place I lived, rescuing as much historical detail as they could going along in the process. They converted it to office space. The central atrium went up two or three floors to a beautiful antique ceiling.

One day a giant crash was heard as a 12'x14' chunk of antique plaster and lathe ceiling fell all the way down to the floor. No one was sitting at the conference table thank goodness because it was destroyed.

The cause? AC condensation on the drain lines for the same had just been oozing into the ceiling and after many, many years it just gave.

Like your situation, it was just water.

I think you should have the AC people out to provide you with some options for your situation. And I don't mean to be melodramatic. Perhaps they can add some localized and enhanced dehumidification to the system or at least come up with some means of capturing the condensation and draining it off somewhere.
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Old 06-17-2011, 10:40 PM   #5
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A solution to your problem would be to insulate your ductwork and that will prevent the condensation from forming.
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Old 06-18-2011, 06:39 AM   #6
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x2, insulating your duct work will help, if not eliminate the problem.

Condensate is caused when the cold ducts are meeting the warm air. Put an R-Value in between the two to separate them, and increase your efficiency.
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Old 06-18-2011, 01:48 PM   #7
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Actually, I have no idea if there is condensation in the ducts. And they are insulated - flex ducts (look like tin foil and have a layer of insulation then layered core). It's the vent that I see the condensation on, although perhaps there is some in the duct.

This happens to be on the shortest run from my AC - about 4 feet. So probably the coldest air coming out there.

Again - it only happens when the door is left open as the temp must rise in the room (or very moist outside air comes in). But again - with kids and parties - we're always in and out of that door.
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Old 06-18-2011, 03:32 PM   #8
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Insulation will solve the problem.
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Old 06-19-2011, 01:18 PM   #9
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Insulation probably won't help. Sounds like condensation is occurring on the cold vent boot lip, which can't really be insulated. You need to decrease the humidity in your basement. Do you have a return in the basement to take the humid air back to the evaporator? A kludge fix is to insert a 12-20 foot flexduct supply loop in place of the current 4 foot supply duct.
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Old 06-19-2011, 03:33 PM   #10
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Don't leave door open for long periods of time.


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