Winter condensation problem in HVAC duct system

Hi, This year I'm using a whole-house humidifier on the 2nd floor of our 2-story home. Yesterday I found that there was quite a bit of condensation forming both inside the attic (insulated) ductwork, and on the surface of the ductwork between the duct itself and the insulating layer. I could squeeze the insulation and feel that it was full of water in a couple of spots. I cut out that insulation, and installed fresh insulation and re-taped everything.
I've got separate ceiling mounted sends/returns in each room. I plan on covering each with a vapor barrier (7-mil plastic and either tape or magnet strips). Questions:
1. Will the vapor barrier on each send/return do the trick? That is, is this solution good enough to fix the problem?
2. How worried should I be about the remaining damp insulation or the inside of the ducts still being wet? We have another 2 months of winter here, so the system will not be drying out on it's own anytime soon. Do you think it's okay to just wait until summer when the attic will get up to over 110 (F), and it will dry out on its own? Or should I do something sooner? I don't want to start a mold experiment up there.
3. If I need to proactively dry the system out now, what is the best way to do that? I am thinking that I could turn off the whole-house humidifier for a couple of days to get the air inside the house to equalize in humidity to the outside (dry) air -- then just run the HVAC air handler fan for 24 hours to pull inside air through the duct system, hopefully drying it out (?)
Any help/insight would be greatly appreciated....thanks....
-Randy
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You have some serious problems that need immediate attention. You've already started a "mold experiment". Don't cover any supply or return vents. That will just compound the problem by keeping moisture in the ducts. The mold is already starting to grow. If you wait until summer, the mold will grow faster.
You don't say what kind of system it is. Your humidifier should only run when the blower is on. If it doesn't, get the idiot back who installed it.
You need to dry things out quickly and completely. Turn off the humidifier for the rest of the winter. Turn the thermostat fan switch to on and leave it there 24/7 for the rest of the winter. Monitor the moisture coming out the supply registers. Do this before your family develops serious health problems.
Read this:
http://www.energystarhomesamerica.com/mold.html

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OK, thanks for the response. The humidifier is a portable unit that sits on the floor upstairs -- it's not integrated into the system (actually, I should not have said "HVAC" -- it is really just an "AC" system).
No way I can leave the air handler fan on for the entire rest of the winter. Also, the humidity level in the house during winter drops as low as 20%, at which point we run into respiratory issues with a couple of family members.
So, I have to figure out how to dry this system out and have humidity control. You don't think sealing off the vents, assuming I can get the system dried out, will be enough?
-Randy
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Maybe I wasn't clear enough. You have a SERIOUS PROBLEM. You are risking the health of your entire family. If you think respiratory problems from dry air are bad, wait until someone develops an allergic reaction to mold. You can't afford NOT to leave that fan on 24/7, at least until all the attic ducts are COMPLETELY dry, and monitored for at least a week.
You need to get a contractor to properly install a good quality whole house humidifier in your first floor system.
Do NOT seal off the vents, and DO leave the fan ON. You need to do some serious reading about mold. It is absolutely DANGEROUS. Don't be stubborn or stupid or cheap. Don't play games with your family's health. If you already read everything on that other link, and STILL are not convinced, read this:
http://www.epa.gov/mold/
Did I mention this is SERIOUS.

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Gotcha, thanks. I will make sure the system is absolutely dried out.
Now, let's dial the clock back to before I turned on the freestanding whole-house humidifier. Assuming my ductwork was bone dry at that point in time, if I put a good vapor barrier over each of the send/ return ducts in each of the rooms -- would that have been good enough to keep moisture out of the system?
-Randy
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You can never make the system absolutely dry down to 0% humidity. There will always be some moisture up there. Even if you could get it to 0% and completely sealed the vents, some moisture would get into the system from the attic.

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Probably. If I was trying to solve your problem I might try to fashion some plugs out of styrofoam that would fit behind the air grilles.
Here's what one manufacturer recommends: When a Unico System for cooling only is installed in an
unconditioned space and used in conjunction with other
heating systems, such as in-floor heating, baseboard hydronic
or electric ceiling cable or baseboard, and adequate
humidification is being provided then it is imperative that
the winter shut-off plugs be inserted into the Unico System
outlets to prevent condensation inside the duct work.
All return air openings must also be blocked
off.
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Here's some more information from the same manufacturer:
Winter Air Shut-off
For cooling only systems where the air distribution system
is located in an unconditioned space, such as the attic or an
unheated garage or utility room, steps must be taken to
keep moisture from collecting in the duct and plenum system
during the winter months. Winter supply air shut-off
plugs are included in the Installation Kits. They can also be
ordered separately in kits of 20 as UPC-42-20. These plastic
plugs fit into the supply outlet opening. Push them in
until they seat against the ledge inside the mouth of the
supply outlet (see Figure 12).
In addition to the winter shutoff caps, be sure to seal the
return air opening. Use both plastic sheet and tape to seal
the filter in place or wrap the filter with plastic so that no
air enters the return.
BE SURE THE HOMEOWNER UNDERSTANDS
THE WINTER SUPPLY SHUTOFFS
AND THE RETURN AIR SHUTOFF PLATE
ARE TO BE INSTALLED AT THE BEGINNING
OF THE HEATING SEASON AND
MUST BE REMOVED WHEN THE COOLING
SYSTEM IS STARTED IN THE SPRING.
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Perfect...this is the type of info I was looking for, thank you. I realize I can't get the humidity level to zero -- I should have said "remove extraneous (pooling) moisture/condensation").
So, my game plan is:
1. shut off humidifier for a couple of days, to equalize RH level in the heated area of the house and the attic 2. run the air handler until the ductwork is free of pooled moisture/ condensation (as long as it takes) 3. seal every send and return with plastic/tape -- good solid vapor barrier 4. turn humidifier back on.
Thanks, Randy
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