Condensation and moisture are pretty much inevitable when living the vanlife. While it is normal occasionally and at a certain level, precautions should be taken during the van conversion by selecting the appropriate materials & techniques, but care should also be taken after the conversion in the day-to-day. Ignoring this issue could turn your van into a fungus incubator... Sharing your home with mold colonies could lead to serious health issues, no jokes. And once the molds invite themselves to the party, it's almost impossible to kick them out definitely. And on the short term, living in high humidity environment is uncomfortable. That's plenty of reasons to do something about it!
Table Of Content
1- Prologue
WE ARE NOT ALONE.
An aircraft is basically a big van with wings.
No, really, we mean it: it’s a big box made of metal and has humans in it. So they share the same moisture problem, and a lot of money is invested in understanding and controlling moisture as it’s leading to multiple problems: it “rains” on passengers and electronic equipment, condensation is trapped on sheet metal (skin) and creates corrosion issues, gallons of water accumulate in insulation (a.k.a. blankets) and at the bottom of the fuselage (there are drain valves, but they sometimes get plugged with dirt). So aircraft manufacturers spend big money in R&D to understand and control nuisance moisture.
Here’s a very interesting and highly recommended article published by Boeing:
This passage is an absolute classic. You shall memorize it:
Because moist air will inevitably come in contact with cold structure, condensation cannot be eliminated. As a result, Boeing chose to evaluate potential moisture-control systems that can help […] minimize condensation, minimize dripping onto equipment and into the passenger cabin, maximize liquid drainage, optimize evaporative drying from wet surfaces and insulation blankets.
2- Theory
Don't worry we'll do this quick.
2.1 - Concepts
ABSOLUTE HUMIDITY (AH)
- Air contains gases (Nitrogen, Oxygen, etc.) and water vapor as well. AH is the total mass of water vapor present in a given volume or mass of air.
- AH doesn't vary with temperature because the amount of water remains the same.
RELATIVE HUMIDITY (RH)
- The amount of water vapor divided by the amount needed for saturation at the same temperature.
- 0% means there's no water in the air; 100% means that the air is saturated with water vapor.
- RH varies with temperature because hot air can contain far more water vapor than cold air.
DEW POINT
- Temperature to which air must be cooled to become saturated with water vapor.
CONDENSATION
- Water that collects as droplets on a cold surface (below dew point) when humid air is in contact with it.
2.2 - Think Inside The Box
This is a box filled with air:
- It’s sealed, so nothing can come in/out.
- It has a given amount of water in it under vapor phase (AH).
- Air has a given relative humidity (RH).
If temperature is increased:
- AH: Remains the same (no water was added into the box).
- RH: Lowers (hot air can contain more water vapor).
If temperature is lowered:
- AH: Remains the same (no water was added into the box).
- RH: Increases (cold air can contain less water vapor).
Skeptical?
Reality Check (no heat source)
- If our FarOutVan is left alone for a few days (no humans, no heat, no ventilation), it should act like our box above right?
- With the help of the awesome SensorPush sensors (faroutride.com/sensorpush-review), we plotted this graph which is exactly in line with the theory above!
Reality Check (Webasto)
- Now let’s fire up the Webasto and see what happens…
- Yep, it works! Let’s continue with more theory then.
Neat, we just found a way to lower the relative humidity (RH): HEAT!
Don’t celebrate too fast because these will add more water to air (and therefore increase AH):
- Humans and pets (breathing and sweating).
- Cooking.
- Damp clothes.
- etc.
Dang, now what?
Increasing temperature will lower the RH, but it’ll get too hot in that box…
- What about exchanging the air from inside with fresh air from outside?
- It’s a good way of getting rid of water that was added by humans, cooking, etc.
And even better...
Ventilation + heat will lower the AH, RH and keep the ambient temperature to an acceptable level!
Wait... we created a...
… A DRYING MACHINE!
Back to our box
Condensation happens even if ambient air is below 100% RH…
- Here, we have a nice ambient T° (68F) and RH (50%).
- At 68F and 50%, the Dew Point (TD) is 48F. It means decreasing the air to 48F will bring RH to 100% (and vapor will turn into liquid on surfaces).
- Because the T° outside is cold, it lowers the surface below Dew Point.
- The closer the air gets to the cold surfaces, the cooler it gets, the higher RH gets.
- T° of air in contact with cold surfaces is below Dew Point (TD), so there is condensation.
So what?
The solution is to add insulation so that the T° of the surfaces (inside) are above the Dew Point!
- The dew point is now somewhere inside the insulation; if the insulation is perfectly impermeable to water vapor, we eliminated the condensation issue!
- We’re still in the “THEORY” section, so that works. In the real world, it’s hard to achieve…
3- How To Control Moisture And Condensation In A Van
3.1 - Moisture Sources
These increase the absolute humidity level by evaporating water in the air:
Respiration and Transpiration
- At rest: about 50 mL per hour per person (that's 400 mL overnight).
Cooking
- More or less, about 250 mL of water is evaporated when cooking a meal.
Propane Combustion
- A 10,000 BTU burner produces 450 mL of water per hour.
- Water vapor (H2O) is a product of propane combustion: C3H8 + 5O2 --> 3CO2 + 4H2O
Drying Stuff
- Guesstimate: 250+ mL per day.
- Dishes, dish cloth, boots, jacket, etc.
TOTAL
1L to 3L of water is added each day in the air, contributing to increased MOISTURE CONTENT.
3.2- Mythbusters
We’d like to start with ideas that are frequently mentioned in discussion forums or Facebook groups. Please make the Internet a better place by NOT RECOMMENDING these! 😉
Moisture absorbants
- TYPES: Clay, silica gel, calcium oxide, calcium sulfate, etc.
- A.K.A.: Cat litter, desiccant, moisture absorber, etc.
- WHY THEY DON'T WORK: They're made for small spaces (storage box, small closet) where no moisture sources are present. They can absorb between 10% and 40% of their weight, depending on the type. Best case scenario, 1kg will absorb 400g (i.e. 400ml) of water. One would need to use a few kilos each day to control moisture and condensation in a van. It's just not sustainable! (unless it's being used for a storage box or a small un-vented drawer, for example)
candles
- Candles create a zen mood and warm your heart, but that's about it.
- WHY THEY DON'T WORK: Water vapor is a product of combustion, so a burning candle actually adds water in air (but nothing substantial to worry about). At 100 BTU/h, it won't increase temperature in the van either (so no effect on RH).
3.3- Ventilation
Ventilation is critical to control moisture and condensation. It replaces the “polluted” inside air (charged with moisture, CO2, carbon monoxide, cooking smells, etc.) with “new” fresh outside air. A functional ventilation system must have exhaust(s) and intake(s).
3.3.1- EXHAUST
ROOF FAN
EXHAUST OR INTAKE?
Hot air rise towards the ceiling. Remember that hot air is able to contain far more water vapor than cold air? While the hot air near the ceiling might be at an acceptable relative humidity (RH), it contains more water vapor by weight. By having the fan in exhaust mode (catching ceiling’s hot air and pulling it outside), more water is thrown out of the van (as well as other pollutants)! Therefore, we always run the roof fan in exhaust mode.
MAXXFAN OR FANTASTIC?
The Maxxfan has an integrated cover that prevents rain from entering the van, even when the fan is running. On the other hand, the Fantastic is basically like a big hole-in-the-roof: its cover must be closed when raining. To compensate, the Fantastic has a sensor and will automatically close when it detects water. But it’s when it rains that controlling moisture and condensation is critical! From our experience, not being able to ventilate when it rains doesn’t make sense. For this reason, we highly recommend the Maxxfan.
3.3.2- INTAKE(S)
The volume of air “removed” by the roof fan must be replaced by the same volume of fresh air, otherwise the ventilation system doesn’t work. In most cases, there is no fan to push the air inside: as the exhaust fan creates a negative pressure inside the van, air is “sucked” into the van by any intake available (windows, holes, cracks, etc.) This is referred as passive intakes.
Keep in mind that a passive intake offers resistance to air flow; too small and your intake won’t be effective (so your ventilation system)! Try it: close all intakes (windows, holes, etc.) and you will hear the roof fan “force” as it cannot pull air outside.
Think of surface area: ideally the intake should have a similar area as the exhaust. For example, the Maxxfan exhaust is 12in diameter; that’s 113in2 surface area. It’s quite large, so a window is ideal as a passive intake. In comparison, a hole of 4″ diameter has 12.5in2 and a 4″ square has 16in2…
It’s also important to note that several small intakes won’t be as efficient as one larger intake (even if the total surface area equals the same), as each one of them offers more air flow restriction. Same with a pipe: this adds restriction too.
WINDOW
If the roof fan is located in the back of the van, cracking the driver and passenger windows open is a good passive intake as the air circulates throughout almost the entire length of the van. Consider adding Rain Guards to prevent rain from entering through the windows:
VAN FACTORY VENT
Not a sustainable ventilation method when parked, but when driving it is an excellent way of venting the interior of the van!
FLOOR VENTS
Adding floor vents helps optimize air circulation, as fresh air enters through the floor and exits through the roof. That’s the strategy we chose for our van conversion, and it’s doing what it’s supposed to (to a certain extent; read “On Second Thought” in each article respectively for our long-term review):
3.4- Heat
While ventilation is the most important moisture-control system, dry heat takes it to the next level: by adding dry heat, we’re pretty much creating a drying machine out of our van!
3.4.1- MOIST HEAT (NON-VENTED HEATERS)
Like it or not, combustion adds water vapor to air. Here’s propane combustion equation (H2O means water…):
C3H8 + 5O2 –> 3CO2 + 4H2O
Burning propane at a rate of 10,000 BTU per hour adds 450 mL of water per hour in the air; that’s a LOT!
Portable propane heaters are not vented, meaning the combustion is internal to the van:
- They burn oxygen and release carbon monoxide inside the van (which is potentially deadly if concentration gets too high. Because of that they're not meant to be used inside; KEEP A WINDOW OPEN AT ALL TIME IF USING ONE, OR YOU MIGHT NEVER WAKE UP).
- They add a lot of water inside the van, promoting moisture and condensation (could lead to mold issues).
- Thermal comfort is lowered as moist heat feels damp and heavy; it's not as comfortable as dry heat.
- They don't have a fan to circulate ambient air, so you can't really feel the heat a few feet away from the heater.
- They are cheap and easy to install.
NON-VENTED HEATERS:
3.4.2- DRY HEAT (VENTED HEATERS)
If combustion produces water, how can we achieve dry heat then? With vented heaters!
Vented heaters are physically located inside the van (or outside sometimes), but combustion is external: air for combustion is taken from outside, burnt, then rejected outside. The heat from the combustion is transferred inside via a heat exchanger. Air from outside / inside is never mixed together. Vented heaters:
- Don't add carbon monoxide inside.
- Don't add water vapor inside; furthermore, by heating the ambient air, the Relative Humidity (RH) is lowered!
- They have a powerful fan to circulate ambient air, therefore heat in the van is uniform.
- They are more expensive and installation is more complex.
VENTED HEATERS:
Webasto
7,000 BTU/h of heat =
0 mL/h of water!
Both Webasto and Espar have been around for decades. And with an extensive dealer network in North-America, you can't go wrong!
ESPAR
7,500 BTU/h of heat =
0 mL/h of water!
Both Webasto and Espar have been around for decades. And with an extensive dealer network in North-America, you can't go wrong!
Snugger
7,500 BTU/h of heat =
0 mL/h of water!
A cheaper alternative to Webasto/Espar. Based in beautiful British Columbia, Snugger offers service throughout North-America.
Propex
6,500 BTU/h of heat =
0 mL/h of water!
A super robust, reliable, and affordable solution if you prefer propane to diesel/gas. The installation is slightly easier too!
Webasto vs Propex
Can't decide between fuel (diesel/gas) or propane? We installed both in our van, so we can help make up your mind!
3.5- Thermal Insulation
We’ve seen that surfaces below dew point temperature generate condensation. That is generally the case with windows (worst), metal (bad) and beer mugs (very good).
Thermal insulation helps control condensation by keeping interior surfaces above dew point temperature. We could easily achieve the perfect insulation with our theoretical box (from “theory” section), but achieving perfect insulation with a van is a bit like chasing unicorns…
3.5.1- THE PERFECT VAN INSULATION
- Temperature varies through the walls (interior finish, insulation, metal). It gets colder as it’s getting closer to the exterior.
- Therefore, relative humidity (RH) varies through the walls as well. The colder the air gets, the higher the RH.
- Condensation happens at the dew point (RH: 100%). Here, in our “perfect insulation”, the dew point is located inside the impermeable insulation; moist air from inside the van cannot reach the location of where the dew point is. In fact, moist air is in contact with the interior finish which is above the dew point; there is no condensation!
Note that metal is totally impermeable to water vapor: it’s a vapor barrier. Moisture cannot migrate through the metal.
Soooo, here’s the bad news: nothing’s perfect in this life. And as a reminder:
Because moist air will inevitably come in contact with cold structure, condensation cannot be eliminated. As a result, Boeing chose to evaluate potential moisture-control systems that can help […] minimize condensation, minimize dripping onto equipment and into the passenger cabin, maximize liquid drainage, optimize evaporative drying from wet surfaces and insulation blankets.
3.5.2- THE PROBLEM WITH INSULATING A VAN
So why is it that “moist air will inevitably come in contact with cold structure”?
Looking at how a van structure is made, we get our answer…
We’re dealing with surfaces that are far less than ideal:
- Hollow regions are impossible to insulate perfectly (even with expanding foam). Frames and structures create thermal bridges (thermal bridges are defined under section 3.5.3). As a result, air is cooled down below dew point locally, and condensation happens in isolated places.
- Uneven geometry creates air gaps where condensation could form and remain trapped.
- Drain holes and openings in frames/pillars allow moist air from outside to infiltrate the insulation layers.
- Minor leaks (from roof and side plastic trims) are a reality. As a result, liquid water can penetrate the insulation layers. (we had reports of small leaks on all platforms: Transit, Sprinter, ProMaster)
3.5.3- REAL-WORLD VAN INSULATION
There’s no doubt in our mind: moist air will inevitably come in contact with cold structure. Denying that fact could lead us to make wrong decisions about insulation. Condensation cannot be totally eliminated, so our approach is to mitigate it (just like in that Boeing article we keep talking about!). Before deciding on an insulation strategy, let’s look at our options:
INSULATION TYPES
- R-value denotes the capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power. It is normally noted "6.5 per inch"; it means applying one inch thickness of the material will provide 6.5 R-value; applying two inches will provide 13.0 R-value; and so on.
Closed Cell Foam Insulation
Closed cell foam insulation has excellent R-value.
Spray Foam
- R-Value: 6.5 per inch.
PROS
- Conforms to curved surfaces.
- Impermeable to water vapor.
CONS
- Can distort the van panels if applied in thick layer.
- Messy to apply.
- Will block mechanism if no precautions are taken (e.g. doors).
Polyiso Rigid Board
- R-Value: 5.6 per inch at 75F, 5.0 per inch at 15F.
PROS
- Impermeable to water vapor.
CONS
- R-value decreases substantially at cold temperature.
- Creates air gaps on funky surfaces (which is mostly the case in vans) = water traps.
XPS Rigid Board
- R-Value: 5.0 per inch at 75F, 6.0 per inch at 15F.
PROS
- Provides more reliable thermal performance than Polyiso.
- Impermeable to water vapor.
CONS
- Creates air gaps on funky surfaces (which is mostly the case in vans) = water traps.
- Maximum service temperature: 165F. (dark painted roof will get hotter than that in the sun! source: phys.org)
NRCA’s most recent recommendations are to assume that polyisocyanurate has R-5.6 / in. when designing for warm climates and R-5.0 / in. when designing for cold climates.
The graph above shows the effect of temperature on apparent R-value of different polyiso products for 4" thickness (expected R-22.4)
Hydrophobic Insulation (doesn’t absorb water)
Hydrophobic material doesn’t absorb and retain moisture. Try it: soak it in water. It does get wet, but water or moisture doesn’t get absorbed into the material, and, therefore, it dries out quite fast.
Thinsulate
- R-Value: 3.3 per inch.
PROS
- Very easy to install
- Doesn't off-gas
- Doesn't lose fibers and not itchy
- Good noise insulation
- Can be stuffed in hard-to-reach places
CONS
- More expensive
Bottom line: it’s a tried-and-true product that gives an added value to higher-end builds.
Rockwool
- R-Value: 3.0 per inch.
PROS
- Easy to install
- Doesn't off-gas
CONS
- Itchy
- Can release fibers
Sheep Wool
- R-Value: 3.6 per inch.
Sheep wool is the new kid on the block, so long term data is not really available except for what the manufacturer claims:
“A chemical-free passive filtration insulating material that manages moisture and reduces sound”
It’s not exactly hydrophobic as it “manages” moisture: it absorbs moisture when ambient air is above 65% RH and releases it below that. The manufacturer claims it prevents condensation on cold surfaces.
Hydrophilic Insulation (absorbs and retains moisture)
No need to say hydrophilic materials are a big NO NO! Some people choose hydrophilic insulation and package it in trash bags to prevent moisture, only to find years later that the trash bags were damaged during installation or after (due to vibration on a metal edge, for example)…
- Recycled Denim
- Fiberglass
Radiant Barrier
A radiant barrier’s purpose is exactly like the name suggests: a radiant barrier! By itself and without any air gap between the metal surface (in other words, if applied directly against the metal), it has pretty much no R-value. That being said, it’s a good material for window covers as it will prevent your van from turning into an oven in summer (but it won’t do much in sub-freezing temperatures).
- Reflectix
Thermal Bridges
Metal is an excellent heat (or cold, same thing) conductor. You can choose the insulation with the best R-value, but leaving any surface of metal exposed to interior ambient air (with no insulation) will create a path for cold (or heat) to sneak inside the van; it’s called a thermal bridge.
Why would one leave exposed metal then? Covering some areas with insulation would reduce the living space too much; frames are a good example. To minimize the effect of thermal bridges, we covered any exposed metal with LOW-E EZ COOL. LOW-E EZ COOL insulation has a flexible foam core sandwiched between aluminum faces. It’s primarily a radiant barrier, but the foam core provide some R-value too. As opposed to Reflectix, it can withstands some pressure without damage and is more silent.
LOW-E EZ COOL
Bottom line: while it shouldn’t be used as main insulation type, LOW-E EZ COOL is a good way of covering thermal bridges.
Vapor Barrier or not?
The purpose of a vapor barrier is to prevent moist air (from inside the van) from migrating towards cold surfaces. The idea is that moist air from respiration, cooking, drying gear, etc. won’t reach cold surfaces and, therefore, that eliminates condensation issues. However, if, for any reason, moist air makes its way past the vapor barrier, it would be very hard to dry that moist air because it would be sandwiched between two vapor barrier layers (remember that metal is a vapor barrier, too).
Even if one could achieve the perfect vapor barrier (which is unlikely, sorry), we’ve seen that there are paths for outside air to infiltrate, and there are potential leak points as well. Therefore, we believe that moist air will inevitably come in contact with cold structure, so our approach is to let the insulation layers “breathe”.
OUR INSULATION STRATEGY
Here is our take on insulating a van: let it breathe. It doesn’t have the highest R-value, and it doesn’t completely eliminate condensation issues, but nothing’s perfect: the best solution is the best compromise!
- THINSULATE covers most large surfaces.
- LOW-E EZ COOL covers frames and protruding structure to prevent thermal bridges. Since it’s a good radiant barrier we partially covered the Thinsulate, but not completely because it’s also a vapor barrier!
- Vapor Barrier: nope.
Don’t get us wrong:
It’s titled “Our Insulation Strategy”. It means we believe there are other ways to obtain good results by using different materials and techniques!
WINDOWS
Windows ARE the weakest link. One can spend a fortune on getting the highest R-value in the walls, but something has to be done about the windows as well!
NOTE: when using the window covers and it’s cold outside, you WILL get condensation on the windows. Indeed, window covers minimize the heat transfer from inside the van to outside; but the small air gap between the window and the cover gets very cold; way below the dew point. So condensation or frost is inevitable. We normally remove the window covers 15-20 minutes before driving and dry them off with a chamois cloth: Buy on Amazon.
Window Shades
Building your window shades from a radiant material is a cheap and good solution for summer or mild cool temps. Reflectix is the material everyone uses out there, but having worked with both LOW-E (EZ-COOL) and Reflectix, we would use LOW-E as it is more resistant, and it doesn’t make that annoying “foil” sound.
Insulated Window Covers
If you are snowchasers like us, insulated window covers are a game changer. They make the interior of the van more comfortable by reducing heat loss significantly (no more cold drafts near the windows!). We made our own from Thinsulate and LOW-E (EZ-COOL); we documented their fabrication in detail!
3.6- Dehumidifier
A dehumidifier catches water vapor present in the air, turns it into liquid and collects it into a container for easy disposal. In other words, it removes moisture from the air.
Are dehumidifiers the holy grail of condensation and moisture control for vans? Keep reading!
3.6.1- How Dehumidifiers Work
By now, we know for a fact that a cold surface condenses water. A dehumidifier is nothing more than an air conditioning unit designed and optimized for collecting water: instead of focusing on blowing cold air into the room, it focuses on refrigerating the surfaces located within the unit, so water condenses on it.
There are two types of dehumidifiers: Compressor and Thermo-Electric.
Compressor Dehumidifier
(Commonly found in houses)
Same principle as a refrigerator (including the 12V NovaKool fridge we have in our van!) and an air conditioning system: this type of dehumidifier uses a compressor to “pump” heat.
- Powerful and ideal for when plugged to shore power.
- Generally works on 120V and draw a LOT of power. Forget it for off-the-grid applications.
- Won't work near freezing temperatures.
Thermo-Electric Dehumidifier
(a.k.a. Peltier)
A Peltier dehumidifier uses thermo-electric principle to convert electricity difference into a temperature difference.
- Draws much less power, and is suitable for 12V operation.
- No moving parts.
- Not as powerful as a compressor dehumidifier.
- Won't work near freezing temperatures.
Compact Peltier dehumidifier (no compressor) with 16 oz. capacity water tank. Make sure to buy the 12V adapter too as it’s more efficient than using your inverter. CURRENT DRAW = 2A (at 12V).
3.6.2- Dehumidifiers help with moisture, but are not the ultimate solution to condensation
If you’ve flown in an aircraft before, you know that the air is so dry it’s very uncomfortable. Yet the Boeing article above confirms aircrafts have condensation issues… what the? Remember that condensation issues are mostly because of cold surfaces. At 36,000ft the outside air is around -70F, so the fuselage skin is very, very cold; the dry air is cooled down so much that condensation happens no matter what.
Now, our van doesn’t experience -70F outside temperatures, but it does get cold out there during winter – cold enough to lower windows and metal temperatures below dew point even if RH is very low.
Let’s play with parameters.
We start with 40% RH and 71F interior temp (which is typical). Condensation happens if windows (or metal) reach 46 F (or lower); that’s relatively high.
Interior RH 40%, Interior Temperature 71F = Dew Point 46F
With the help of a dehumidifier, let’s bring the RH down to 30%, which is the lowest RH that humans are comfortable with. And still 71F interior temp: condensation happens if windows (or metal) reach 38 F (or lower). An outside temperature of 32F will most likely bring a window down 38F. We still have condensation…
Interior RH 30%, Interior Temperature 71F = Dew Point 38F
If we lower the RH down to 15% (which is not really possible in the real-world if people live in it), we still have condensation if windows (or any other surface) get down to 21F (which you will most likely encounter if you are skiers like us!).
Interior RH 15%, Interior Temperature 71F = Dew Point 21F
Bottom word:
A dehumidifier helps with moisture, but won’t completely eliminate condensation. It’s a good idea to use one when parked and plugged to shore power, but it draws a substantial amount of power for those who are off-the-grid (knowing that condensation is most likely to happen when solar power is at its lowest)…
Real-World Check:
We observe the most condensation (on the windows) during winter when it’s cold outside (sub-freezing); because we heat with a vented heater (Webasto), our RH is normally in the 30-35% range. Our ambient air is already dry, a dehumidifier wouldn’t help much; the issue really is with the cold surfaces.
4- Life After The Conversion
MOISTURE AND CONDENSATION CONTROL IN THE DAY-TO-DAY
We did it! The van conversion is over. We chose the best insulation strategy and materials to our knowledge. But the fight is not over! We’ve been living in our van full time since August 2017, and we’re still controlling the moisture and condensation in our day-to-day life:
4.1- Cooking
Cooking during winter is far from ideal: it adds a lot of moisture (from food and from propane combustion, especially the oven) and since it’s so cold outside, ventilation means a lot of heat loss. It is what it is: whatever the temperature outside, ventilation is the key! When we cook, we usually keep our side window opened and run the roof fan.
- Above 35F outside, it’s no big deal.
- Below 25F outside, it gets chilly in the van for a short while. But the Webasto keeps us comfy anyway.
- Down to -15F, the cold draft between the opened window and the roof fan can be pretty brutal. The Webasto runs full-speed! But when we’re done cooking, we close the window and the floor vent is the only passive intake. After the meal, we normally close all intakes.
4.2- Climate
Here’s the worst possible scenario that we’ve encountered: after a day skiing at Crystal Resort (3900 ft at the base) during a relatively warm (28F) and very wet day, we hung our gear to dry and we drove down immediately to a lower elevation so it would be warmer. It was snowing at the resort, but raining at lower elevation. We cooked, and we rested for the night.
Let’s think about it for a second:
- Gear drying (adding moisture)
- Cooking meal (adding moisture)
- Driving down to a warmer place
- Driving down to a more humid place (it was raining full-on)
Nothing wrong with cooking and drying our gear, but we definitely should have stayed at higher elevation where it was colder (more heat from the Webasto = lower RH) and where outside air was dryer (less moisture coming in from the air intake). Now we know!
4.3- Activities
The main reason we live in our van is for riding our mountain bikes and our snowboards more often.
We were very concerned with drying our ski gear in the van at first, but we’re happy to report that our gear is fully dry in about 2 hours (a little more for the 2 pairs of boots). With the Webasto working hard when it’s cold outside, the air inside is dry and comfortable. Nice!
Winter Vanlife
Traction, electricity, finding water and camping spots, staying warm, controlling moisture, drying gear, etc.
It’s actually worse after a day riding our bikes in the wet (think Pacific North West): since it’s warm and moist outside, we can’t really use the Webasto to full capacity or it gets too hot. So gear takes longer to dry. Huh!
4.4- Location
Oh, we probably should have mentioned this at the start of this essay… but look, if you use your van mostly in any of the yellow-ish places below, don’t overthink this moisture and condensation thing! You’re fine, it’s dry enough there…
If, on the other hand, you plan on spending extended time during fall/winter in the Pacific North West (Coast of British Columbia, Washington, Oregon) then this article is definitely for you! Actually, we got the idea and wrote this article while we were here during the rainy months… This amount of water in California would probably create a supra-landslide and make the whole state totally flat 😛
5- On Second Thought
WHAT WOULD WE DO DIFFERENTLY IF WE HAD TO START OVER
We completed our van conversion in August 2017, and we are living full time in the van since then. While we feel confident about our material choices, and we would do exactly the same if we had to start over, time will tell if we nailed it or not. It will be interesting to strip down the van after 10-15 years of usage…
That's it folks, hope that helps!
Thanks For Reading.
Can you provide some tips and insight into a reverse scenario? We are in Florida, high humidity and high heat with a portable AC unit for the summer. We are getting a nice low indoor temp, but the exterior is really high temp and we like everyone see condensation happening.
Is ventilation still key here? We have a maxxair fan in the front and a fresair unit in the back. The Fresair unit doesn’t work in Humid climates which is why we are using a portable AC while down here. We also have CRL window with a T vent that we use. While using the AC, should we crack the T vent and have the fresair and fan on to create the circulation? I feel like the T vent and fresair fan defeats the point of the AC if we just replace the air inside. Any thoughts? Love the site!
Hi!
Not an expert on A/C and hot humid climate, so take my opinion with a grain of salt…
I don’t think venting is beneficial in your situation, as you’ll introduce more humidity in the van. I think A/C lowers the humidity somewhat, but if you need to lower the humidity even more a dehumidifier is the way to go. Dehumidifier are energy-hungry, it’s not really a solution off-grid; but if you’re in a serviced campground then you should be good to go.
Good luck! 🙂
Have you considered leaving an air gap between reflective vapor barrier and van skin and continuosly venting outside air into the gap to maintain lower humidity air against the van skin?
Wow, what a great resource and full of science, thank you! With regards to a vapor barrier, check out Membrain (https://www.certainteed.com/building-insulation/products/membrain/). Membrain creates a continuous air seal and it’s vapor permeable especially at high humidity, which allows the inner wall to dry out. The permeability significantly increases at lower humidity and colder temperatures keeping vapor out of the wall. With regards to ventilation, you might want to check out this Heat Recovery Ventilation (HRV) system (https://foursevenfive.com/lunos-ego/). It will set you back $795 but it recovers 85% of the heat!
Antoine – since you have SensorPush sensors, you might even try an experiment to manage moisture within your system. One of the tricks used in curling clubs, which are usually steel skinned pre-fab metal buildings, is to operate the HVAC heating system under positive pressure. So rather than venting the van, have you tried closing your passive vent, pulling air into the van with your fan while heating, rather than venting it? By running fan on suction, you pull cold dry air through the nooks and crannies (at least in a Denver climate). This isn’t nearly as effective as pushing warm dry air out through the nooks and crannies and allowing it to dry out the hidden spaces and exfiltrate from the van. At first you may increase condensation as you displace humid air from the van, but as you heat dry air it will dry things out….. check out this article….. https://www.buildingscience.com/documents/digests/bsd-119-summer-condensation-problems-in-ice-arenas
(my comment was too long, so I split it…)
We had a slow water leak in our van this fall, it went unnoticed for a while because it was so slow but it made the subfloor very very wet. We were lucky that we were able to get it dry without any damage, but it took three weeks and involved a week of running a large industrial dehumidifier. One thing we noticed is the dehumidifier raised the temperature in the closed van quite a lot. So another reason you might not want to run a (smaller) one in your van is if you don’t want excess heat… e.g. you are in Florida
Have you tried drip drying clothes under an awning in damp areas to get the initial dripping water off before drying them inside? I’m considering adding loops to my awning so we can hang stuff.
…”Therefore, we always run the roof fan in exhaust mode.”
We mostly run our roof fan in exhaust. Here are the normal exceptions…
1) when cooking. We put an opening window behind the cooktop. We put the fan on intake and open the window so it pushes the steam and smells from the cooktop out of the window instead of dragging it through the van.
2) when we want warmer (sun heated) air coming in
3) when someone is doing something smelly outside, e.g. we are in a parking lot and someone is smoking. Reversing the fan can sometimes make a big difference.
4) when one of us is on the bed and one is on the toilet. The fan is over the bed and it can draw smells to the person in bed. We hit reverse and the airflow goes towards the toilet, not away from it. It can make a very big difference.
Also we have found that the humidity in the van when cooking is reduced by putting a lid on pans whenever possible. We often don’t bother at home but we always do in the van.
We found the disposable dehumidifying bags very useful when we moved our (closed) boat from the east coast to the west coast. We were warned that we could have damp problems as there would be no ventilation (electricity had to be turned off and hatches closed) and it would be going through tropical areas. We put plenty of the bags in areas of the boat and found they had absorbed a bunch of moisture. Might it be useful to use these if you are going to store your van for any length of time? I understand your logic of not using them in daily travels.
Hi there. I really appreciate your website! I’ve been following for a few years now.
A question for you on trapping moisture between vapor barriers; it looks like you installed the Thinsulate before the EZ Cool. With the smooth mostly moisture impenetrableness of the EZ Cool might you put the EZ Cool directly on the metal and then the breathable Thinsulate next so that the vapor barrier (the metal) and the somewhat vapor barrier ( the EZ Cool) are next to each other allowing on one possible vapor barrier?
Thanks for so much valuable information.
Not sure if I understand the question correctly, but we recommend installing the Thinsulate directly on the metal per: https://faroutride.com/thinsulate/
There is not much gain if you add the EZ-COOL under the Thinsulate.
What a brilliant article, thanks so much. I’ve just discovered that I’ve got a build up of condensation behind my less than perfect vapour barrier. But now I know how to tackle it.
Rather than going for an overly ambitious hermetically sealed principle, I’m going for plenty of ventilation instead.
Much appreciated
Great post. Lots of helpful information. Very nice. I have a few additional strategies for keeping the RH down whilst living in a vehicle: (1) minimize cooking meals that involve lengthy boiling. If you’re looking for some grainishness – I would recommend Cous Cous – get the water boiling, throw in the Cous Cous and turn off the burner – let it sit for five minutes. Done. Cous Cous is like pasta – you can go savory with some pesto, garlic, olive oil and veggies or sweet with some apple banana, cinnamon and BS for the morning cereal. Cous Cous is straight-up wheat though which is not ideal for those seeking to avoid the glutens. So, boil less water in your rig. Get a Cast iron skillet and make more stir fry and less pasta.
(2) use “swimmers towels” as your towels and also use them to soak up any watery spills in the van – then squeeze-out the offending water outside. I have used a swimmers towel as my personal bathing drying device for a few years and find that I can wring it out to an almost dry state before leaving the gym and getting back in my rig. I have also used these chamois style towels to soak up any leaks that might be coming through during fierce rainstorms. I use them as little water vacuums – Always trying to eliminate water and wetness from the interior of my rolling house.
Isabelle and Antoine – Can I just say, this is by far the most informative, entertaining, SOUND articles out there addressing condensation issue in a van. There’s the difference for Engineering-minds (aka, everything is lined out very logically for us). THANK YOU! One question (if you’re still up for Q&A), what are your thoughts on wood burning stove? Wondering if they fall under dry heat or moist heat category. Again, thank you guys for sharing the amazing information.
A wood stove would be considered dry heat. Personally, we wouldn’t want a wood stove in the van because:
1- Wood is not always available;
2- These small wood stove burn rather quickly and we don’t want to have to wake up in the middle of the night;
3- We like to program the Webasto to start (about) an hour before we come back in the van after a day of skiing; I wouldn’t let a wood stove burn without surveillance.
4- Smoke smell in the van;
5- Not stealth (we often park in residential street in winter).
Maybe for a weekend van, but for full time it’s just not practical in our opinion.
Cheers!
Wood burning stoves dry the air. Their door is shut, and it is a dry heat. For those of us with serious dry eye problems trying to protect our corneas, they and any form of dry heat is a real problem. Need the moisture in the air; just not next to the outer surfaces. Arrrggg!
Great website and article! When building for the southeast (hot humid summers, May-Oct, is the issue of insulation and condensation as significant as colder, wet climates. I would think that heavily insulating your van would actually help keep heat and humidity in as well. Would the main concern be good ventilation and airflow?
I think proper insulation combined with proper ventilation is the key for a good climate control. So you’re set for year-round and for travelling anywhere!
This article is amazing, and your website is basically our bible as we’re planning our build!
Question for you – we’re considering buying and converting a van in November/December, when it will be wet and snowy outside pretty much constantly (we live in Seattle). Should we be worried about this from a condensation perspective? I know that that’s a huge problem while living in the van, but I don’t know if I should be worried about that as we build. If yes, are there ways to mitigate that or should we just drive and build it someplace warmer?
We built ours during fall/winter as well (in Quebec), no issues!
It’s refreshing to see people take the condensation issue seriously. So many van-builds on youtube that you can tell will end up being moisture traps behind the walls. Building science has been dealing with these same issues for many years in houses and I’m happy to see that you guys are doing your part in bringing van builds to the same level of quality found in modern houses.
Hi Guys,
I’m trying to follow in your footsteps and as many of others have told you, your site is amazing. The quality of the content, the design, the personality, the passion – all of it. I was hoping to get your perspective on a few things. I have the same transit and layout you do and am looking for hot water and heating. While I’m not in the van yet (so we’ll see), I plan to be in a mix of cold and mild climates and can’t decide on my heating system. I’m not wanting to do propane (for humidity and other reasons) and am pretty sold on some sort of a webasto or similar heater. I would like to do a radiant flooring that uses glycol running through PEX in the floor that is heated by the webasto hydronic heater. I was planning to use a heater that directly heated the glycol, then just use a valve to control whether or not the heat mostly blows out via the fan, or gets distributed via the coolant (due to the open valve). My overall goals are even heat distribution throughout the van. I’m planning on primarily sheeps wool insulation and am on the fence about adding windows. Now that you know my situation here is where I would appreciate your opinion and experience. You seemed to have heat distribution issues (hence the duct in the back), do you feel my radiant/hydronic solution here would be adequate to overcome this? Or should I get a fan to distribute the heat? (I’m not sure if I’m kidding or not) Another alternative would be to centrally locate the webasto and then run ducts with directional and open/close adjustable vents around the cab. With the duct strategy I worry about adequate positive pressure to push the heat through all the ducting. So what do you think? Option A – Diesel Hydronic heater with a valve and PEX lines? Option B – Good ol’ diesel heater with a fan (The easiest). Option C – Diesel hydronic with ducting (A more advanced version of your duct added from the start with a centrally positioned heater)? Thanks in advance for sharing your experience, expertise and opinion. Someday I hope to buy ya’ll a delicious brew on a mountain top somewhere. Cheers!
Hey Brian – I just saw a youtube video about installing a hydronic underfloor system in a van. Looks like he’s using PEX and has both underfloor and a fan coil unit. It’s all proprietary, however you might be able to get a little info on the website. Have a look: https://www.vanlifetech.com/hydronic-heating-systems
PS – this is an awesome write up and blog. HUGE kudos for the attention to detail and thoughtful process for dealing with building envelope challenges within the van.
Really good articles.
Do you have added any insulation to cockpit area? (Other than windows cover) This tread was mostly covering cargo area.
Thanks for your dedication at documenting your knowledge.
Indeed, we added Thinsulate above the headliner. It’s documented here: https://faroutride.com/thinsulate/
Cheers!
Great read. Fitting out a van, and all your ideas are so helpful. Thankyou !!
I stumbled across your blog and it’s been so informative! I live in Alberta, Canada and am considering moving into a van and building it up myself but there are a lot of things to weigh before making a go of it in the winter up here..
I’m just leaving a comment to say that your articles are the most informative and helpful of anyone’s out there. I learned more about condensation here than in months of readings, and almost no one really discusses ventilation. Your other articles are similar quality.
There’s also many nice discoveries, such as the fact that BC has aquatic centers. Your article about parking is more complete than what I’ve found before. etc. etc.
Thanks!
Any thoughts on Isolina (flax) for insulation? It’s supposedly ideal behind wooden construction if you want to use natural materials, but what will happen when its laid next to the metal interior of a van?
Appreciate your thoughts on this!
Hi, I’m not familiar with this sorry!
Fantastic article! Thank you fir all of the time and effort it took to write it! I am now much more confident moving forward with a first time build in a few months.
Good to hear!! 🙂
This article was SO HELPFUL! We just moved into our van and live in the Midwest…winters are COLD and our first week was a mess of condensation. Reading this was exactly what we needed (the builders of the van built it out exactly as they should have, we just didn’t quite understand how everything worked!). Anyway, just wanted to say thank you!!
Good to hear, glad we could help!! 🙂
Excellente explication du phénomène de l’humidité et de la condensation. Important à bien maîtriser dans la conception et la vie quotidienne en VR.
Bravo
This site is a gold mine! You are really making a huge difference in our plans for our van and it’s going to be so much better thanbks to you!
I was wondering if you had an opinion on using a wood stove as a solution for heat and humidity.
I can deal with the hassle of getting wood and cleaning the ashes but I wouldn’t want something that adds water in the air.
Looking at somethink like the Cubic cub mini stove.
I’m also up in Vancouver so we are expecting a ton of humidity. 🙂
For full time living, I honestly wouldn’t want to deal with wood. Sometime (very often actually) you just want heat QUICK without hassle. And what if you have to stay in a residential street or something? I wouldn’t use the wood stove there…
Personally we’re not fan of wood stove for vans (even if we LOVE fireplace), but if that’s what you want, we see many vans with chimney. We have no experience with them so can’t really comment.
Cheers!
Thank you for the excellent information. Did you ever have problems with snow building up on the roof and blocking the maxxfan when you would get 1-2 feet over night? Would you ever consider putting a maxxfan on the back vertical wall of the van to address this issue? I am planning my first build for a 2o20 transit on order! I want it to be a winter focused ski van!
Of course we have to shovel the roof on really big dump, cause the Maxxfan (and solar panels) are buried under. No big deal, it’s kindof fun.
I wouldn’t install the fan on a vertical wall, it belongs on the roof (for proper ventilation and installation considerations, plus you’ll get tons of dust inside when driving if installed on the back door).
Cheers!
Great overall site for van conversions. I am in the planning stage now and have found your site invaluable. I don’t see any mention of wanting an air conditioner. It seems this is only possible when using shore power but do you find it necessary when in hot climates?
Isabelle and I don’t handle the heat very well, so we’re staying out of hot climates! We spent the last summers in British Columbia where it can get quite hot, but AC is not mandatory.
For us, good ventilation is the key: https://faroutride.com/mosquito-screens
Cheers,
antoine