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Old 02-09-2010, 09:59 AM   #1
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Duct condensation


Two weeks ago I closed on a bank-owned home that had been sitting vacant for about 13 months. A few days ago I noticed a small wet spot had formed in our living room ceiling. The spot is new and I'm pretty sure I noticed it right away. It also coincided with the first time we had run the AC continuously for any significant length of time.

I located the spot in the attic. It is directly underneath a junction where four ducts come together. I had to prop up the foil junction box (sorry not sure of technical term) in order to photograph the accumulated moisture beneath it. Here are some photos:

http://www.diychatroom.com/members/i...-5959-600x400/

http://www.diychatroom.com/members/i...-5960-600x400/

I can't find any holes or leaks in the box. All I found was condensation between the bottom of the box and the chip-board shelf it sits on. The chip-board has two saturated areas that are visible in the photos. Moisture must be going completely through it and onto the drywall ceiling.

A friend recommended that I wrap the junction box in thicker insulation, then run the AC and watch for condensation up in the attic. He also suggested that I feel the newly insulated box with my hand after the AC has run for awhile and if it feels close to room temperature then that is a good indication of adequate insulation.

I'm willing to try this but getting the insulation onto the box is my main problem. It has four ducts running into it so I can't simply wrap it several times in insulation.

Do I need to disconnect the ducts first, then wrap the box, then cut holes through the insulation for the ducts to reconnect?

How do I disconnect the ducts and then reattach? Is any adhesive or sealant involved for are they attached with something like ring clamps or large zip ties?

I appreciate any help you can offer.

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Old 02-09-2010, 11:37 AM   #2
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Duct condensation


Interesting. That looks like a ductboard box which is already insulated. Are you sure that is the only source of your moisture? No other vent pipes in the area like a bathroom exhaust?

The other ends of the flex duct pipe, do they terminate somewhere that is not insulated, like a register boot, or the supply plenum from the air handler?

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Old 02-09-2010, 02:39 PM   #3
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Duct condensation


Go to your thermostat and turn the fan switch to "on".
Go to that box and feel for air leaks.
Cold air blowing out of it will condense the moisture on to it, and anything its touching.
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Old 02-10-2010, 10:24 AM   #4
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Duct condensation


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Interesting. That looks like a ductboard box which is already insulated. Are you sure that is the only source of your moisture? No other vent pipes in the area like a bathroom exhaust?
No the nearest bathroom exhaust is a good ways away.

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The other ends of the flex duct pipe, do they terminate somewhere that is not insulated, like a register boot, or the supply plenum from the air handler?
One of the flex pipes in the photo does go to the point where my air-handler connects through the garage ceiling (it is not physically in the attic though. My air-handler sits vertically in the garage).

Possibly related to my condensation problem - the grate over the return in our living (which passes through to the garage and is directly underneath the air-handler) has rust spots all over it. I didn't know if these two things were related or not.

Thanks for your help. I will stick with this thread and try anything you guys suggest.
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Old 02-10-2010, 10:25 AM   #5
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Duct condensation


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Originally Posted by beenthere View Post
Go to your thermostat and turn the fan switch to "on".
Go to that box and feel for air leaks.
Cold air blowing out of it will condense the moisture on to it, and anything its touching.
Ok I will give this a try tonight and report back.
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Old 02-10-2010, 12:56 PM   #6
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Duct condensation


It does sound more like a leak then a lack of insulation.

If you do find a leak just seal it up with some duct tape and run AC.


Report back your findings and we can try to help more if need be.
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Old 02-10-2010, 06:08 PM   #7
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Duct condensation


I ran the AC for a good 20 minutes and sat next to the junction box, feeling all around and underneath it. I couldn't see, feel, or hear any air leaks, and no new moisture developed. The outside was room temperature to the touch as were all the ducts around it.

Ok, it turns out I'm an idiot and it probably is a leak after all. Before when I said there was no vent anywhere near the moisture, what I meant was that no vents originate near it. BUT, today I realized the dryer vent tube is routed right over the wet area, and indeed the place where the vent tube hits the underside of the roof is directly above the junction box beneath which I found the moisture

So in the interest of solving what is now surely a leak, here are a few more photos:





It looks to me like dirty water has run down the outside of that vent tube. You can see the streaks and residue pretty clearly in the photo.

Here's another clue I only just learned of today. My wife tells me the dryer is taking a really long time to dry clothes.

So, is the leak likely caused by a gap in the flashing or tar paper? Or, since there's an issue with clothes not getting dry, could the vent be blocked or clogged, then filling with water, and THEN running inside the attic somehow???

Thanks for sticking with me on this guys, I really appreciate it.

Last edited by imhotep; 02-10-2010 at 06:21 PM.
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Old 02-12-2010, 12:52 PM   #8
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Duct condensation


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Originally Posted by imhotep View Post
So, is the leak likely caused by a gap in the flashing or tar paper? Or, since there's an issue with clothes not getting dry, could the vent be blocked or clogged, then filling with water, and THEN running inside the attic somehow???
Quite possible both. The dryer not drying well suggests a clogged vent. Did you have rain just before you noticed the leak?
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Old 02-12-2010, 12:59 PM   #9
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Duct condensation


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Quite possible both. The dryer not drying well suggests a clogged vent. Did you have rain just before you noticed the leak?
No, but southern FL is getting hammered as I type this. Tonight when I go home I will inspect again and see if I can tell what's up. What I really need to do is snake the vent tube or drop a camera down there to see if there is a clog.

THEN, if the clog gets cleared up and I still get leaking, I guess I'll know it's a roof leak.
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Old 02-13-2010, 11:46 AM   #10
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Duct condensation


Check the pipe for restrictions and clean as needed.

The streaking you see on the outside of the pipe could be from condensation. If so, insulate the pipe and that should resolve that issue.

If it is not from condensation, it could be improper installation of the vent assembly on the roof and will need to be sealed up to fix the roof leak. This would take place on the roof, not inside.

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Last edited by AndrewF; 02-13-2010 at 11:49 AM.
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