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Old 06-26-2010, 01:24 PM   #1
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Where does the moisture come from?

I have read the many threads on humidity inside Airstreams and ways to control it. The bigger question is how does so much moisture get into a closed up trailer?

We store our 34' in a covered and screened from the sun area beneath our house. We live in coastal South Carolina--humidity is nothing new. We keep the unit fully closed (all windows, vents, door, storage compartments, etc. are shut and locked tight). All of these penetrations to the skin have gaskets in good conditon (no known water leaks). The belly pan is fully intact and penetrations are sealed. All the seams of the skin are factory riveted and sealed with Vulkem. The roof is coated in white Ceramiflex. The refrigerator compartment to the exterior is sealed from the interior (in case the ammonia releases in won't be discharged into the interior). The exterior furnace vents (what, 2" in diameter) are not sealed, but they could be in a temporary manner during storage and they are the only openings that I can think of.

Anyway, this unit is about as air tight as can possibly be. I run a dehumidifier inside 24/7 365 and get a gallon or better of water everyday. How is all this moisture migrating into the trailer? It is baffling to me how a metal trailer can be so permeable? Suggestions?
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Old 06-26-2010, 08:13 PM   #2
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Nothing is as airtite as one might think. Moisture can pass through the wooden floor if no where else. If it is humid outside of the trailer it will be humid inside. It would probably be best to open the roof vents and crack a couple of windows. This will allow the trailer to "breath." You can continue to control "excess" humidity with the dehumidifier.

You said "beneath our house." Is it in a basement? On concrete? Whatever the immediate outside environment is will determine what is going on inside of the trailer. Running a fan for air circulation may be just as effective as running the dehumidifier.

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Old 06-26-2010, 10:22 PM   #3
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Roger, thanks for your insight. Cracking windows and vents would defeat the idea of running the dehumidifier and when we did it that way before, the oak cabinetry swelled so much the cabinet doors wouldn't close and we had a musty, old trailer smell. With it closed up and dehumidifier running those two problems go away. The dehumidifier maintains the humidity level at about 55%.

How does moisture migrate through the plywood floor if a fully intact bellypan is in place? Not being sarcastic in the least, I simply don't understand how humidity can travel through sealed aluminum.

To answer what 'beneath our house' means: The first floor of our house is elevated about 11 feet off grade. It is common around here to build elevated to get living space out of potential flood zones and because a basement is simply not doable here. The area under the house serves as a garage and is fully enclosed (the concrete slab is actually 6" above flood so the garage can be closed in legally--meets flood regs). The Airstream currently is stored on a concrete slab underneath a screened porch off the rear of the house and that area is not closed in with hard walls (1x4 lattice) so it is exposed to the outside air but no direct sunshine on it. We live on a tidal marsh with a river a quarter mile out into the marsh so we might be a little more humid than some other areas.
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Old 06-26-2010, 10:43 PM   #4
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Originally Posted by Cantrell View Post
I run a dehumidifier inside 24/7 365 and get a gallon or better of water everyday. How is all this moisture migrating into the trailer? It is baffling to me how a metal trailer can be so permeable? Suggestions?
Are you talking about the gallon a day in the dehumidifier? Are you actually staying inside the trailer during that time? [in latter case, one or more people's respirations discharge a lot of moisture]
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Old 06-26-2010, 10:58 PM   #5
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.. how does so much moisture get into a closed up trailer?.. I run a dehumidifier inside 24/7 365 and get a gallon or better of water everyday. ..?
We have run dehumidifiers in 4 campers over the last few years...and also get gallons a week...
There are dozens of air paths into the shell...they all allow air exchanges and bring the moisture along for the ride. Just yesterday I was flushing the freshwater tank by pulling the big-o-plug out of the bottom and noticed the cool air falling out from the air-conditioned interior thru the access panel.

I think the WHY is too complicated but the solution to a dry stored camper is EXACTLY what u r doing...run the dehumidifyer. I actually ran a drain hose thru the floor on one of my trailers and let it drain on the ground.

I ran my AC for the last week and 1/2 and it steady dumped gallons of water out the drain...but it is rather crispy inside
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Old 06-27-2010, 07:32 AM   #6
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Where does the moisture come from?

The air.

The water you are collecting indicates that the dehumidifier is working. Not that you have a moisture problem with the camper.
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Old 06-27-2010, 07:53 AM   #7
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Are you talking about the gallon a day in the dehumidifier? Are you actually staying inside the trailer during that time? [in latter case, one or more people's respirations discharge a lot of moisture]
No, not staying inside. This is during storage. It can go for a week or two sometimes without me ever going inside to check on things so no doors flapping and no one making humid breath in there. The dehimidifier sits on the kitchen counter and drains directly into the sink which discharges through a slightly opened waste valve. If I catch the water that comes out for a day, it is usually around a gallon. I know some is evaporating out of the traps and have read of people putting vegetable oil in the traps (not comfortable with doing that) but I think that amount is minimal and is caught again by the dehumidier. The dehumidifier comes out when we travel and the a/c does the work then.

Look, I know that an Airstream is not a hermetically sealed unit but a gallon a day just seems like an awful lot of water from such a small space that appears to be relatively well sealed. My brother says I should do a smoke test to see where the air is actually transferring. Might be a good idea.

Thank you all for your input.
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Old 08-22-2016, 01:43 PM   #8
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I realize this is an older thread but I was perusing and thought it still germane, and wanted to offer something that might prove helpful.

The last poster seemed to believe his Airstream, when closed up tight, is fairly well sealed against the ingress of humidity... yet it should be fairly obvious that cannot be the case when a gallon or so of water is extracted from it with a dehumidifier.

It should come as no surprise to anyone that air will expand as it is warmed, and contract when it is cooled.... a cycle which happens every day to a stored airstream. If there were no pathway to exit/enter then the Airstream would develop wrinkles and cracks in short order. Every day the air warms and exits the trailer, and every night, fresh, moist air re-enters it. Closing the windows and doors will not prevent that. (It's why intakes and exhausts and crankcase vents are closed, or should be, on stored internal combustion engines to reduce internal rust and corrosion.)

However, opening a few windows and vents will allow that moist air to depart again with the next cycle and reduce the need for dehumidifiers except in the most humid, coastal environs.
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