Water in AC ducts

I am getting a LOT of water (enough to drip and rust the metal covers) through several widely-spaced overhead registers. There is no sign of water damage to the ceiling, so it's not coming in that way - the water is *only* on the metal registers. I recently had the system checked out (routine seasonal inspection) and they found no problems. I mentioned at that time that I had noticed water on one of the register covers (kitchen) and the service person said it was probably just condensation from water already in the house. But now I'm seeing liquid water on registers in rooms with no water vapor sources. The house is only 6 years old, I had the original cheapie A/C unit outside replaced last summer, and had no water problems until a couple of weeks ago.
Before some wiseacre asks, Yes, I have called the local installer, but he's very backed up and won't be able to come out to my rural location for a week or more. It looks like there's mildew already getting started in the ducts. I've only had 2 bad asthma attacks in my life, and both were triggered by mildew, so I'm concerned about the problem becoming permanent (or at least very expensive; there is no easy access to the overhead ductwork). Any ideas where to look first? Shouldn't any water that gets into the system be precipitating out at the condenser?
Thanks!
-Rich
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Hummm, so the humidity is so high that its causing water to condensate on the registers eh... Interesting problem. You did check to make sure that the system itself is draining right?? (the blower should have a drain on it to get rid of water that condenses on the coils)
Unless of course your house has a excessively high humidity problems, thats a completely different issue.
The other problem can be that the system is oversized for the house. If that's the case the system wont run long enough to remove humidity out of the house. Things like that can be fixed by adjusting the fan speed to lower setting to let the unit run a bit longer to get rid of the humidity.
Tom
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Are the ducts uninsulated or underinsulated in a hot area.
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m Ransley (webtv officionado) wrote:

Is that a question? And who in the hell are you talking to?
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If the register boot s not sealed where it penetrates the drywall ceiling, attic air can be mixed with the cold air at the register causing the register to sweat. Just had another one do that today.
Remove the register, seal around the boot with white silicone caulk. Let the silicone cure for 24 hours before you put the register back or you will glue it to the ceiling.
Other things that will make registers sweat besides what Turtle said is a closed damper or low air flow at any register. Also if a window is cracked open where the register is (because you want to add fresh air).
By the way, it is not the heat in the attic that can cause the ducts to sweat, it is the humidity. The heat actually reduces the chance for sweating. Heat is assumed to cause sweating because it is usually accompanied by high humidity, but the humidity is what makes the problem. (Look at a psychrometric chart.)
Stretch
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Not the problem. There is NO staining around the 3 registers showing the condensation. I've had a roof leak fixed before, so I know what wet plaster looks like. If any part of the duct/register was getting condensation on the *outside* in the space between roof and ceiling, the ceiling would be showing the moisture. It isn't - ONLY the metal register.
So, ready for the solution? I finally convinced the A/C company who did the installation and regular servicing to have one of their newbies crawl around under the house (I can't - bad back) and he found one of the "flex joints" (his term) had been torn away on the cool side of the system (downwind of the condenser). The system is apparently picking up moisture by infiltration when the fan's not running, then depositing it on the cooled metal registers when the condenser/fan cuts on. That explanation also accounts for the inability of our oversize unit to keep the house as cool as it did last summer.
Kinda cute, really: The kid comes back out and asks if I've got cats. "I can see their claw marks". On sheet metal, right. He is from the city, recently moved up here, and has never seen a 'possum or raccoon (aside from road kill) or the damage they can do...we've got both in abundance around here. I've shot 'em and trapped ;em, and they keep on coming. I'm thinking about paying to have the areas around the exposed ductwork covered with hog wire.
-Rich

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That is probably the problem or his ducts (in the attic) are not insulated. Even if the "runs" are insulated, it only takes a small surface area of the boot (for the ceiling registers) to exposed to the heat in the attic to make them sweat buckets.....
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This is Turtle.
Here is some causes.
Low air flow through the ducts to have a high temperature differencial of the air going in and the air coming out the discharge registers. you can have 30F+ differencial and when it hits the room air condition air. It will form moisture. Causes Dity filter, too many register shut off, or dirty evaperator coil to restrict the air.
Poor insulation around discharge registers box and will form moisture.
You have R-4 rated Flex Ductwork and the attic is getting over 140F+ in the attic. The flex duct connections and the Register will sweat in that heat in the attic.
TURTLE
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BUT - the brand new outdoor unit was installed at the height of the summer heat last year (mod-July) and worked flawlessly. It is no hotter/cooler this year than last year - no environmental difference. Well, hurricanes came through, but we only got rain and a little wind - no roof damage, no leaks. And there is NO condensation showing anywhere on the ceiling plaster, even directly in contact with the registers - only on the metal itself.
See the solution posted elsewhere in the thread. It was obvious once located. And thanks everyone for the ideas and efforts!
-Rich
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