How to Stop Condensation in an RV: A Comprehensive Guide

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Are you wondering how to stop condensation on your RV windows?  Finding mildew in your camper's closet?  Trying to discover the cause of your damp mattress?

If you're using your RV in winter, especially living in it full time, you very well may encounter these problems.  In this blog post, I am going to help you understand the causes of these common RV problems and what you can do to solve or prevent them.

What causes condensation inside an RV?

Simply put, condensation occurs when warm, moist air comes into contact with a cold surface (or cold air).  If you want to understand the scientific explanation more fully, you can Google terms like “dew point” and “relative humidity”, but for the purposes of this discussion, the short version will suffice.  The main sources of condensation in an RV are:

• Warm, moist air from outside entering a cold RV and hitting cold interior walls and windows.  This can happen when it's hot and humid outside and air conditioned inside (or in early spring when RV is still cold inside from being in storage all winter).
• Warm, moist air produced inside an RV hitting cold interior walls and windows.  This often happens when people use RVs with poorly insulated walls and single-pane windows for winter camping or for full time living in cold climates.

Regardless of the cause, the results are the same: your things become damp, mold and mildew to form, and airborne allergens such as dust mites thrive.

How to prevent condensation from occurring

The best way to stop condensation is to eliminate its cause.  All of the tricks and techniques for doing that really boil down to two things:

• Reduce indoor humidity.
• Remove cold surfaces and air pockets.

So how do you do that?  Below are some ideas.  If one doesn't work for you, maybe another one will!

Ways to reduce humidity inside an RV

First of all, you need to know what the humidity level inside your RV actually is.  The best way to do this is to buy an inexpensive hygrometer / thermometer.  Ideally, your indoor relative humidity should be between 30%-50%.  Once you've identified that your humidity level is indeed a problem, you can try the following:

Run the air conditioner.

Leaving your RV windows open during summer in a humid climate may cut down on your electric bill, but there's a tradeoff, as air conditioners remove moisture from indoor air.  If it's hot enough to run the AC, this alone may solve the problem.

Open a window or ceiling vent.

I know, that's the opposite of what I just said!  But if the inside air is more humid than the outside air, opening a window or ceiling vent can help some of that humidity escape.  Keep in mind that hot air rises, so a ceiling vent is going to work better than a single window.  This is especially important while doing activities that create a lot of extra water vapor, like showering, cooking on the stove, or releasing the pressure from your Instant Pot. 🙂

Increase air flow.

Running a fan can help evaporate condensation and evenly distribute the air temperature throughout your RV.  If you have a window or vent open, a fan will help the humid air escape more quickly.

Run a dehumidifier.

If you aren't wanting to also cool your indoor air, a dehumidifier can help you remove moisture from the air.  Dehumidifiers come in a range of sizes and prices; you just need to make sure you get one designed for the amount of space you're using it in.  Additionally, you'll want to pay attention to how many pints of water it holds (especially if your humidity level is extremely high); the more it holds, the less frequently you'll have to empty it.  If you don't have room for one the size that you need, you could try using a couple of small ones instead, and if you're not sure what size will work, you might start with one and then add a second one if needed.

Use moisture absorbers.

When you're boondocking or your RV is in storage and running an electric dehumidifier isn't an option, crystal moisture absorbers such as Damp Rid can help pull moisture out of the air.

Avoid creating extra water vapor.

Showering, cooking indoors, and hanging clothes to dry inside the RV all raise the indoor humidity and fog RV windows, so if you've tried everything else and you're still having problems, doing your laundry at a laundromat, using campground shower facilities, and cooking outdoors as much as possible may help.

Ways to eliminate cold surfaces where condensation can form

If you can eliminate cold air and cold surfaces from your RV interior, you won't have to worry as much about lowering the indoor humidity level.  Why?  Because cold air has a lower dewpoint (the temperature at which the air becomes saturated and condensation forms).  Warmer air can hold more moisture.

Additionally, cold exterior walls, floors, and windows not only cause condensation, they also mean you're leaking costly heat.  By beefing up your RV's insulation, you'll not only reduce condensation, you'll also spend less money on propane or electricity, and your RV will feel less drafty.

Here are some ways to warm up cold surfaces and other cold areas in your RV:

Insulate single-pane windows.

For those of you living in an RV during the winter, if you do nothing else, do this.

Many RV owners put Reflectix in their RV windows to help insulate (sometimes they remove it during the day to let in light), but personally, I am not a fan of that method for insulating RV windows, and here's why:

• If you use it during the day, you're keeping a wonderful source of free heat (the sun!) out of your RV.
• If you only use it at night, then during the day your windows can get very cold and allow heat to escape and cause the RV to feel chilly.  I know this because I sit on the couch in my RV next to a window all day every day, and I can feel a huge difference with and without those windows being insulated.
• It's kind of expensive!
• There are better (in my opinion) alternatives.

So what are those alternatives?  Funny you should ask, because it just so happens that I wrote a whole separate blog post about all the different ways I've tried insulating my RV windows for winter.  You can see the difference made by one of those methods, plexiglass, demonstrated above next to a fogged-up window without insulation.

Warm up the floor.

A warmer floor can help the temperature inside your trailer or motorhome stay warmer and more even, which, in combination with air circulation, can help warm up cold corners that invite condensation to form.  The best way to keep the floor warmer is to skirt your RV, but adding rugs, perhaps even with foam mats underneath, may also help.

Insulate RV slide-outs.

Another thing that can make a big difference is sealing any drafts around your slide seals and adding an extra layer of insulation under and/or around them.  We tape foam board to the bottoms of all our slides for winter, and it makes a significant difference in the temperature of the air near the floor.  (We used duct tape our first winter but have since learned to use foil HVAC tape instead – it stays sticky during all kinds of weather, but doesn't leave behind any residue when you peel it off.)

I have also stuffed weather stripping around the gap between my slide trim and the wall (on the inside of the RV).  Some custom skirting companies also sell a wrap that goes around the walls of your slides to help block wind, or you could make your own, perhaps out of billboard tarp vinyl or Reflectix.

Target cold closets and cabinets.

In cold weather, the air inside RV closets and cabinets typically stays colder than the rest of the RV since doors prevent the heat from entering.  Colder air has a lower dew point, meaning condensation can form at a lower temperature, so even if you're not seeing condensation in the main areas of the RV, it might be forming in the back of a closet or cabinets.

One way to prevent this is to open all your cabinets and closets regularly to equalize the temperature.  I know of one RVer who opens all her cabinets every night.  If that sounds like too much work, another option is to put moisture absorbers (such as small containers of Damp Rid) in each cabinet.  You could also try making your own moisture absorbers out of old socks filled with crystal (silica) cat litter.

Another thing you can do that may help is to add an extra layer of insulation to the exterior walls of your cabinets and closets.  I have used Reflectix for this purpose in the past, but I've heard some people say moisture can get trapped behind it.  Then, one of my subscribers told me about a product she used to insulate her closet, and I loved the idea, so I decided to try it myself.  Not only does my closet look way better, now the walls have an added 1/4″ or so of water-resistant foam covering them.  If you have really thin, poorly insulated walls, this might even be an option for other walls in your RV to help stop some of the cold from coming through.  I wrote a blog post about this project if you'd like to read more about it.

Solve damp RV mattress problems.

If you are finding the bottom of your mattress or the area under your bed damp (or worse, moldy), here are some suggestions, in addition to what's already been mentioned, for dealing with the problem:

• Check the temperature of the bed platform or the floor underneath.  If it's 10-20 degrees colder than room temperature, add extra insulation to this area if possible.  If you can access the area under the bed platform (or under the floor, if you have a floor under your bed), adding a layer of foam board would be a good way to do this.  Just make sure you don't leave any gaps where air can accumulate with no air flow.
• If you have an empty space under your bed, this would be a good place to set a container of DampRid.
• If you're not able to warm up the area under your bed, at least make sure your mattress isn't coming in contact with a cold surface: place something under your mattress that will allow air to pass underneath so that moisture can evaporate instead of accumulating.  You can buy products designed specifically for this purpose, or you may be able to come up with your own DIY version (if you do, I'd love to see a picture!).
• Protect your mattress and prevent moisture from your breath and body from seeping into the mattress while you sleep by using a waterproof mattress cover.  (You can get them for RV sized mattresses on Amazon.com.)

Buy a four-season RV (or plan to spend the winter someplace warm).

I don't want to be “that person”, because I know everyone's circumstances are different, and with enough determination, it is possible to survive winter in just about any type of RV (well…maybe not a pop-up camper…but who knows–maybe there is someone out there doing it!).  There's actually a really helpful Facebook group I'm a part of called “Winter RVing: Let's Stay Warm Together!” full of people living in the northern U.S. and even Canada in all kinds of campers (some of them are even heating their RV's with wood stoves)!  So I know that theoretically it can work.  But if you're shopping for an RV or still trying to decide whether you can feasibly live in an RV during winter weather, know that having a four-season RV really does make a difference (though even then you'll still probably have to do some winter preparation).

Key takeaways if you're struggling with condensation or mold:

• If possible, warm up any surfaces where condensation or mold is occurring by adding extra insulation or increasing airflow to closed-off spaces.
• Measure the humidity level of your RV with a hygrometer and, if it's higher than 50% in a warm RV or 30% in a cold RV (for example, an RV in storage), lower it with a dehumidifier (for whole rooms) and/or moisture absorbers (for cabinets, closets, or when you don't have electricity).

Click here to read about the other ways we prepare our RV for winter!

For more winter RV tips, check out my Winter RVing Resource Page: