Camper Van Condensation: Why It Happens and How to Stop It
Condensation forms when moist air touches cold glass or bare metal. Keep indoor humidity below 60 % (EPA), ideally 30-50 %. Ventilate with a roof vent fan, insulate without thermal bridges, heat with dry diesel or electric heat instead of an unvented propane heater, and add a desiccant dehumidifier in cold weather.
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Condensation appears when warm, moist air touches a cold surface, such as a window or bare metal, and in a camper van or RV it is fixed by lowering humidity and warming those surfaces. Keep indoor humidity below 60 %, as the EPA recommends. Ventilate with a roof vent fan, insulate without thermal bridges, use dry heat and add a dehumidifier if that is not enough.
This guide explains why it happens, the targets to aim for and a step-by-step plan that works in winter.
Why does condensation form in a camper?
Because a small cabin fills with water vapor, and cold surfaces turn it back into water. Air holds more moisture when warm. When it touches glass or metal colder than itself, the extra moisture condenses as droplets.
A camper has lots of cold surfaces and little air volume. The usual water sources are:
- Breathing and sweating, especially overnight with the rig closed.
- Cooking, above all boiling water without a lid.
- Drying clothes, towels or wet gear inside.
- Propane heaters without an outside vent, which release water vapor with the combustion gases.
Diesel and electric heaters do not add moisture, because diesel heaters send their combustion gases outside and electric heaters burn nothing.
What humidity should I aim for?
Below 60 %, ideally between 30 and 50 %, according to the EPA (EPA, mold and moisture). Above 60 % for long periods, mold becomes likely.
You cannot manage what you do not measure. A thermometer-hygrometer such as the Govee H5075 shows humidity on its display and, per its listing, in an app. Read it in the evening and first thing in the morning.
| Reading | What it means | What to do |
|---|---|---|
| 30-50 % | Ideal range | Keep your current routine |
| 50-60 % | Acceptable, watch it | Ventilate more while cooking and sleeping |
| Above 60 % | Mold risk over time | Ventilate, dry heat and a dehumidifier |
| Wet windows or walls | Surfaces are too cold for the humidity | Insulate, cover windows, lower humidity |
How do I stop condensation step by step?
Work in this order: ventilate, remove moisture at the source, heat dry, insulate, then dehumidify. Each step makes the next one work better.
- Ventilate continuously. Run a roof vent fan on exhaust at a low speed and open a small gap on the opposite side so fresh air can enter. A fan with a rain cover or rain sensor can keep running in wet weather. See the best RV roof vent fans.
- Boost the fan while cooking. Put lids on pans and run the fan on high until the steam clears. Cooking is often the biggest single source of moisture.
- Dry wet gear outside or in a closed bag. Towels and jackets drying inside release water all night.
- Heat with dry heat. Diesel and electric heaters do not add water vapor. A propane heater without an outside vent adds both water vapor and CO. Compare dry options in the best diesel heaters and the best electric space heaters.
- Insulate walls and roof without thermal bridges. Closed-cell foam does not absorb water, and glued to the metal it reduces condensation behind it. Uncovered ribs and pillars stay cold and drip. Our van insulation ranking explains each material.
- Cover the windows. External covers stop cold before it reaches the glass. Internal covers are easier but let condensation form between the cover and the glass, so wipe it in the morning.
- Add a dehumidifier if humidity stays high. Choose the type by temperature (see the next section).
- Air out bedding and cushions. Lift mattresses during the day so the underside can dry.
Which dehumidifier type works in a camper?
In cold weather, a desiccant model; in mild weather, any type with a real daily capacity. The type matters more than the brand.
| Type | How it works | Cold weather | Water removed | Best for |
|---|---|---|---|---|
| Compressor | Cools air over a coil until water condenses | Performs poorly | High in warm, humid air | Warm climates, large RVs on hookup |
| Desiccant | A drying rotor absorbs water; the unit warms the air | Works better at low temperatures | Medium to high | Winter vanlife, parked rigs |
| Peltier (mini) | A small thermoelectric plate condenses water | Weak | Very little | Closets, tiny spaces |
| Absorber (no power) | Calcium chloride or silica gel soaks up water | Unaffected | Very little | Closets, rigs in storage |
Read the daily capacity, not the tank size. The Ivation IVADDH09, a desiccant unit, declares 9 L (about 19 pints) a day and a range down to 33 °F (1 °C). Peltier minis in our catalog declare between 0.45 and 0.75 L a day, and some listings print the tank size in the title as if it were the capacity. Our ranking of the best RV dehumidifiers compares them on real capacity.
Check the power draw too. A dehumidifier on battery power runs down your house battery quickly. Use the RV power calculator to see how many hours it will run.
Where does condensation hide?
Behind panels, under mattresses and inside cabinets on outside walls. Those spots are cold and get little airflow, so moisture sits there unseen.
| Spot | Why | Fix |
|---|---|---|
| Behind wall panels | Warm air reaches bare metal | Insulate against the metal, closed-cell foam where possible |
| Under the mattress | Body heat and moisture meet a cold base | Lift it daily; a slatted or ventilated base helps |
| Cabinets on outside walls | No airflow, cold wall | Leave doors ajar; insulate the wall behind |
| Window frames and seals | Coldest part of the window | Wipe daily; external covers in winter |
| Roof vent surround | Thermal bridge at the opening | Insulate around the frame |
What works best for most rigs?
A roof vent fan running low, dry heat and good insulation solve most cases; a dehumidifier is the backup. The Maxxfan Plus 00-04550K is reversible and, per its listing, can run with its lid closed, which is useful in rain. If you spend winters parked, a desiccant unit such as the Ivation IVADDH09 adds real capacity in the cold.
For an overview of fans, 12 V fans and dehumidifiers, start at ventilation and damp.
Frequently asked questions
Why is my camper van wet inside every morning?
Your breath and any cooking add water vapor overnight, and it condenses on the coldest surfaces: windows and uninsulated metal. Run a roof vent fan on low with a small opening elsewhere, and keep humidity below 60 %.
Does a propane heater cause condensation?
Yes. A propane heater without an outside vent releases water vapor as well as CO into the cabin. Diesel and electric heaters give dry heat. Never sleep with a propane heater on.
What humidity should I keep in my RV?
The EPA recommends indoor humidity below 60 %, ideally between 30 and 50 %, to prevent mold. A thermometer-hygrometer shows you the figure.
Should I crack a window in winter to stop condensation?
Yes, a small opening plus a roof vent fan on low swaps moist air for drier outside air. You lose a little heat, but a dry heater replaces it, which is far easier than drying out wet insulation later.
Which dehumidifier works best in a cold camper?
A desiccant model. Compressor dehumidifiers lose output in the cold, and Peltier minis remove very little water. The Ivation IVADDH09 is a desiccant unit that lists a range down to 33 °F (1 °C).