Condensation And Moisture In A Van | Why It Happens And How To Control It

Moisture-Condensation-Control-Van-Heading-(Fullpx)

Condensation And Moisture In A Van | Why It Happens And How To Control It

An Essay By:

Logo-FarOutRide-512px-(novbr-2019)

Introduction

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.

Denying 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! 

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Portrait

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 create 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 an very interesting and highly recommended article published by Boeing:

Controlling Nuisance Moisture in Commercial Airplanes

Boeing.com

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.
Sealed-Box-Moisture-AH-increase

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.
Sealed-Box-Moisture-ventilation

And even better...

Ventilation + heat will lowers the AH, RH and keep the ambiant temperature to an acceptable level!

Sealed-Box-Moisture-ventilation-and-temperature

Wait... we created a...

… A DRYING MACHINE!

Drying-Machine-Doodle

Back to our box

Condensation happens even if ambiant air is below 100% RH…

  • Here, we have a nice ambiant 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… 
Sealed-Box-with-insulation

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:

Moisture-Condensation-Control-Van-Conversion-Sources
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 increase  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-Condensation-Control-Van-Conversion-myths
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 days 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).

Moisture-Condensation-Control-Van-Conversion-VENTILATION

3.3.1- EXHAUST

ROOF FAN

EXHAUST OR INTAKE?

Hot air rise towards the ceiling. Remember that hot air is able to contains 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 polluants)! Therefore, we always run the roof fan in exhaust mode.

MAXXFAN OR FANTASTIC?

The Maxxfan has an integrated cover that prevent 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 

Maxxfan-Surface-Area
4-in-circle-area
square-area

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 its 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 take it to the next level: by adding dry heat, we’re pretty much creating a drying machine out of our van!

Moisture-Condensation-Control-Van-Conversion-DRY-HEAT

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 ambiant 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:

Mr Heater Buddy

9,000 BTU/h of heat=
405 mL/h of water!

Olympian Wave 8

8,000 BTU/h of heat =
360 mL/h of water!

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 ambiant air the Relative Humidity (RH) is lowered
  • They have a powerful fan to circulate ambiant 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…

Moisture-Condensation-Control-Van-Conversion-INSULATION-UNICORN

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.

Perfect-Van-Conversion-Insulation

 

 

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 structure 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 happen 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)
Real-World-Van-Conversion-Insulation

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 take wrong decision about insulation. Condensation cannot be totally eliminated, so our approach is to mitigate it (just like in that Boeing’s 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 have 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 decrease substantially at cold temperature.
  • Create 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

  • Create 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.
Polyiso Apparent R Values Temperature Effect
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 loose fibers and not itchy
  • Good noise insulation
  • Can be stuffed in hard-to-reach places

CONS

  • More expensive

Bottom word: it’s a tried-and-true product that gives a 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 ambiant air is above 65% RH and releases it below that. The manufacturer claims it prevent 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

Radiant barrier 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 a 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 ambiant 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 word: while it shouldn’t be elected 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) of 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 EZ-COOL and Reflectix, we would use EZ-COOL 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 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 dehumidifier the holy grail of condensation and moisture control for vans? Keep reading!

Moisture-Condensation-Control-Van-Conversion-DEHUMIDIFIER

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 on 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.

 

  • Draw 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 flew 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 cool 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 else) 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 ambiant 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 worst 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!

MOUNTAIN BIKER'S GUIDE TO SQUAMISH, WHISTLER AND PEMBERTON

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 😛

Google Earth North America Dry Regions

5- On Second Tought

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.

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about us

Nice To Meet You.

Hello! We’re Isabelle and Antoine 🙂 In 2017 we sold our house (and everything in it), quit our engineering careers and moved into our self built campervan. We’ve been on the road since then and every day is an opportunity for a new adventure; we’re chasing our dreams and hopefully it inspires others to do the same!

42 thoughts on “Condensation And Moisture In A Van | Why It Happens And How To Control It”

  1. 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!

    Reply
  2. 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!

    Reply
  3. 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.

    Reply
  4. 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!!

    Reply

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