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hello,

i'm in VT right now where temps are getting into the single digits at night. keeping van at ~55F overnight w/ a space heater plugged in to a friends house. humidity has been very low - 16% to 35% max.

condensation is forming against the interior roof of the van, behind 1.5" of thinsulate.

i don't have an exhaust fan YET, but i wish i did :)

my questions
1 - how worried should i be about the ice on the inside of the roof? is it a big concern? how quickly will rust start to happen?
2 - what is the best way to dry the van out? i can heat it up in there but it seems like the ice just melts (maybe evaporates and then re-condenses - not sure) and then re-freezes.
3 - any tips on preventing condensation from forming in the future (aside from installing an exhaust fan)? would i be better off NOT running the space heater or keeping temps as low as tolerable? would cracking a window or 2 help?

THANK YOU!
 

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2020 Transit Cargo LWB AWD 350
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At least you aren’t using a propane space heater, those pump out moisture like a fire hose. Venting is your friend, but honestly, a roof vent fan to actively suck the moist air out is part-and-parcel of the foundation van build, even before insulation goes in. If you have no unpainted metal yet, I’d say rust could take some time to form but you need a plan for some very low humidity over several days for things to dry out. Humans in the van will keep adding moisture. Can you get it out of the weather where you can have doors/windows open? How long before you can install the vent fan? Read up on what “dew point” is, and how you can avoid that happening inside your van. I doubt the electric space heater is making things worse, other than how the temperature differential from outside to inside creates that dew point on interior surfaces. Colder could be better unfortunately.
 

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22 148 Cargo M Roof AWD Oxford white .
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Air space / air pockets between metal skin and thinsulate ? Sounds like the problem .
if thinsulate is proper glued to the metal skin with 3m90 I don‘t think you
would have this issue.
 

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since you have electricity available, I'd put a fan in to keep air circulating and crack a window. Won't be as good as a roof vent as the warm hot air rises and is condensing on the cold roof, but it will help until you can get a proper roof vent installed. A dehumidifier would also help if you have access to one.
 

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2018 T350HD Dual Sliders - SOLD
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Start the van, crank up the heat, and TURN ON the A/C so the condenser runs and dehumidifies the interior. If it is single digits outside, open the door after the interior gets too hot, and let the cold outside air steal some of that moisture from your van.
 

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Make sure mold does not start growing on the thinsulate.

 

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I wouldn't be so worried about rust forming on the inside of the roof - at least in a short time period - as it should be painted. BUT, I would be concerned about saturated insulation/mold, etc. That doesn't take long to become a problem.

As others have mentioned, air flow is absolutely key. I one time (years ago) found a windshield leak in my car and as a result the flooring and all the padding/carpet was soaked. It was January (up north), and I thought heat would be the solution. A friend who was a physics professor said, nope, MOVING AIR is more important. Of course moving air and heat is even better. And he was right: i had been heating to not much avail. Added fans and air flow and what a difference that made in drying everything out. (And of couse I fixed the root problem of the leak.)

So (as mentioned in previous posts) do whatever you can to get air flowing, and add heat if you can. As @GapRunr mentions, cold/dry outside air could also be your friend. Winter cold air is generally quite dry (at least up north where I'm from).

In future, as also mentioned: You don't want gaps between the sheet metal and your insulation. That makes cold pockets where water can condense (like the ol' frosty glass of icy beverage on a hot day). You may want to consider long term re-doing that insulation. Maybe adhering it more thoroughly to the roof, maybe using something like extruded polystyrene glued in place, or etc.

Air flow doesn't have to be made by a Maxx Fan (they have their drawbacks), but they are a proven way to keep air moving (even in winter, cracked open slightly). Something like the smaller round Dometic or (I forget the other brand name) could also work (they are like 8" in diameter and you push the lid straight up plus they have a fan).
 

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2020 High-Extended AWD EcoBoost Cargo with windows
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I can't assure anyone (including myself) if these work... but they have turned colors when it's been really humid... and change back after plugging them in. And seem to decrease moisture on the windshield when placed there behind the cover, so... maybe? I've been running one in the cab area and another in the rear. 🤷‍♀️
 

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Use a de humidifier designed for low temperature conditions.

Most of the normal versions remove moisture by cooling the air down to ~ 50 - 60 F and condensing out the water as a liquid. The cooling is done by "pumping the heat" from the colder coil to a warmer coil. The air is re-warmed on the way through - so the heat is recycled and fairly efficient.

Low temperature versions cool the air down to ~ 25 F and literally freeze out the water on a coil - sort of like a refrigerator that is not frost free. They pump the heat between coils in a similar way.

Not cheap but very effective.
 

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1. You need ventilation

2: this is exactly why I did my roof and upper cavity insulation the way I did. Roof has 1” polyiso sheets glued into the cavities with great stuff pro. All gaps around the boards filled with great stuff. I’ll put some thinsulate up there too inbetween the polyiso and my plywood ceiling panels as well once those go up again. There is no exposed exterior skin of the van in the upper half of the van for moisture to condense on.

The upper wall cavities would have been a pain to glue in the polyiso, so I just carefully used great stuff pro to line the cavities. Have to be careful to make sure it doesn’t fall away from the wall while it’s setting. I’ll put a layer of thinsulate in front of the foam before putting up the wall panels as well



Food Ingredient Recipe Cuisine Dish
 

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Use a de humidifier designed for low temperature conditions.

Most of the normal versions remove moisture by cooling the air down to ~ 50 - 60 F and condensing out the water as a liquid. The cooling is done by "pumping the heat" from the colder coil to a warmer coil. The air is re-warmed on the way through - so the heat is recycled and fairly efficient.

Low temperature versions cool the air down to ~ 25 F and literally freeze out the water on a coil - sort of like a refrigerator that is not frost free. They pump the heat between coils in a similar way.

Not cheap but very effective.
Where is Orton when you need him, He is always talking about his 12 volt dehumidifier.
 

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Be sure to use a vapor barrier on the warm side of insulation.
 
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1. You need ventilation

2: this is exactly why I did my roof and upper cavity insulation the way I did. Roof has 1” polyiso sheets glued into the cavities with great stuff pro. All gaps around the boards filled with great stuff. I’ll put some thinsulate up there too inbetween the polyiso and my plywood ceiling panels as well once those go up again. There is no exposed exterior skin of the van in the upper half of the van for moisture to condense on.

...
It seems like this is one of those "only do A" versus "only do B" things. I appreciate the /concept/ of leaving no gaps anywhere... but if that were really the answer, why does Ford (and every other vehicle manufacturer... except who knows WTF Telsa might do :rolleyes: ) go the opposite direction: gaps and air-flow everywhere?

It seems to me like the glued-shut is asking for more trouble when the inevitable gap creates a moisture-pocket that now has trouble venting / dehydrating. 🤔

Don't get me wrong... I really don't know. But when I look at the glued-shut stuff, all I can see is the myriad paths to get air and moisture back behind that stuff - through the roof ribs, for example... or even past the spots where the foam-sealing that holds the outer-van-skin to the inner skin.

Is this another of those moot debates like which ground point to use? And what floor or insulation? Or whether to lift an AWD rig? ;)
 

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I truly don't think moisture will ever get behind the polyiso or great tuff. It sticks well to the metal. There's also no single seal around the perimeter of each sheet or anything like that - almost every square inch is glued to the wall essentially. (I was pretty careful about doing a layer around and inbetween all the little gaps between the outer skin and inner support skin and roof ribs where ford's adhesive foam is. The foam itself is waterproof. I will leave holes in my wall panels so air/moisture can still get out of those cavities. The cavities won't be "sealed" from the interior of the van.

Mold is my worst enemy - I'm very sensitive to it. I did not want any water condensing and keeping thinsulate wet and allowing mold to grow. Just liek the guy would had thinsulate against his ceiling with some mold spots - because the exterior skin was exposed to moist inside air.

Time will tell I suppose. So far so good.
 
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An average human breathes out around 400 ml per day of water, more than a cup, so no matter what else is going on you need to ventilate while you are inside and ideally run a dehumidifier for a day after using the van.

How much ventilation is enough? About 5 CFM per 100 sq ft of floor area is considered normal for a house, so somewhere around 5 CFM is probably about right. Not a huge amount of ventilation, just a continuous flow of air will do it. Even a little usb fan blowing out a crack in a window is going to be enough, with a second little fan circulating air in the van.

For the current situation, I would heat up the van to about 80 degrees and ventilate it with a small or medium sized fan to circulate air around the van all day long. Based on my experience drying out plumbing leaks, it takes a couple or more days to dry out moisture once it has worked it's way into a structure.
 

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Here’s the short of it. Even at the low end of your RH, that amount of moisture exceeds the dew point at the van’s skin.

You have to reduce the humidity at the van’s skin. I see three options.
1. Dehumidify the space mechanically or chemically.
2. Install a vapor barrier. On the warm side of insulation & thermally isolated from all metal bridging to the skin.
3. Ventilate.

#2 is pretty tough in a van. And if you get up to higher RHs, you‘ll likely just condense on the vapor barrier instead.

#1 is expensive (chemical) or energy intensive (mechanical).

So with good reason, most snow chasers choose option 3.
 

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2021 Crew Van AWD, EcoBoost, 148, HR, Adventure Package
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The moisture WILL get in. Best to make it easy for it to get out.
I think this is the correct approach. In this forum (somewhere) someone added an article from the 50's or 60's from Boeing that showed how teams of engineers worked for a long time to stop condensation on the inside of the fuselage of their planes. Long story short, they tried a lot things to stop the condensation and then decided that was not going to be a thing. The solution became how to direct the flow and dripping and how to dry it out when it happened. Preventing the condensation was not possible given the variables they had to deal with.
 
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