How to Stop Condensation in a Campervan (What We Wish We Knew in 2026)

To stop condensation in a campervan you need to get moisture out faster than you put it in: run a roof fan in exhaust mode with a window cracked on the opposite side, cover every bit of bare metal so it stops being the coldest surface in the van, and cook with the fan on. Condensation is warm, damp air from your breath and your cooking meeting a cold wall or window and turning back into water. It is not a building fault. It is physics, and physics has a fix.

We learned this the slow way. Our first winter in the Boxer, we woke up to windows running with water and a damp patch on the mattress where it touched the back wall. A few weeks later there were little black spots of mould behind the bed. We had insulated, we had a heater, and we still had a swamp. The thing nobody told us is that heating a van without ventilating it just makes the problem worse.

Why does my campervan get so wet inside?

Condensation happens when humid inside air touches a surface colder than the air's dew point. The water vapour gives up its heat and turns back into liquid, right there on the cold spot. In a van the cold spots are obvious once you look: single-pane windows, the metal door frames, the wheel arches, any bare panel you never got round to covering. Those are thermal bridges, places where the cold outside reaches straight through to the inside.

The moisture comes from you. Breathing, cooking, boiling a kettle, drying a jacket over the seat, even a houseplant. Two people sleeping breathe out a surprising amount of water overnight, and a pot of pasta on the hob adds far more in twenty minutes.

Do you really sweat a litre of water a night?

No. You will read everywhere that a sleeping body releases one to two litres of moisture a night. That number comes from mattress marketing, not science. The measured figure for an average healthy adult is closer to 200 ml over eight hours of sleep, roughly 25 ml an hour, from breathing and evaporation off your skin. Two people is maybe 400 ml a night between you.

That still matters in a sealed metal box with nowhere for the water to go. But it also means your real enemy is usually cooking and wet gear, not your lungs. We boiled water for tea, cooked dinner, dried socks on the heater, and sealed everything up against the cold. Of course it rained indoors.

Condensation isn't a sign you did something wrong. It's a sign two humans are breathing inside a metal box. Your job is to give that water a way out.

What is the single best fix for van condensation?

Ventilation, and it is not close. A roof fan running in exhaust mode pulls the warm, moist air up and out before it can reach a cold surface. For that to work you need air coming in too, so crack a window or open a floor vent on the opposite side of the van. That sets up a cross-flow: dry-ish air in one side, wet air out the top.

Counterintuitive bit: leave it running low all night, even when it is cold. A constant trickle of air keeps humidity down far better than a big blast in the morning when the damage is already done. We run ours on the lowest setting every night now and the windows stay clear.

How do I stop condensation on the windows and walls?

Attack the cold surfaces. Anything metal you can still see inside your van is the coldest point and will sweat first, so cover it. We went back and insulated the door frames and panels we had skipped because they were fiddly, and the dripping stopped almost overnight.

For windows, thermal covers or insulated blinds make a real difference. They put a barrier between the warm cabin air and the cold glass, so the air never touches a surface cold enough to condense. A cheap reflective screen cut to fit is enough to start. You do not need a fancy kit.

What about insulation and vapour barriers?

Insulation reduces condensation by keeping the inside face of your walls warmer, so air is less likely to hit a cold surface. The catch is what happens if moisture gets into the insulation. Open, breathable materials like sheep's wool or recycled-PET let water vapour pass through and dry out, which is why they resist mould. Closed setups that trap damp tend to grow it.

Vapour barriers are where a lot of first-timers, us included, overthink it. A vapour barrier only helps if it is perfectly sealed on the warm side of the insulation. One gap and it traps moisture against the metal instead of keeping it out, and you have built yourself a mould incubator. If your van is well ventilated, breathable insulation with no barrier is the simpler, more forgiving choice. Done is better than perfect, but a half-sealed vapour barrier is worse than none.

Does running the heater stop condensation?

On its own, no, and this surprises people. Warm air holds more water, so heating a sealed van just loads the air with moisture that dumps straight onto the cold windows the moment it touches them. We spent a fortnight thinking our diesel heater would dry the place out. It did the opposite until we cracked a vent.

Heat plus ventilation is the combination that works. Warm the space, keep a small amount of air moving through, and the humid air leaves before it can condense. Heat without airflow is a recipe for wet bedding.

A simple condensation routine that works

Here is what we actually do now, and the van stays dry. Fan on low whenever we sleep, with a window cracked on the far side. Fan on high while cooking, lid on every pot. Wet coats and towels go outside or in a vented locker, never draped over the bed. Thermal screens on the windows on cold nights. A quick wipe of any window beading first thing, which takes ten seconds and stops mould before it starts. None of it is clever. All of it is the stuff we wish someone had told us before we found mould behind the mattress.

If you want the full version, our build manual covers the ventilation and insulation choices in order, so you make them once instead of redoing them like we did.

Frequently asked questions about van condensation

How much ventilation does a campervan need to prevent condensation?

At a minimum, one powered roof fan running in exhaust mode plus one passive intake (a cracked window or floor vent) on the opposite side of the van. The fan pulls moist air out, the intake lets dry air in, and the cross-flow keeps humidity from building up. Running the fan on a low setting continuously works better than short bursts.

Why do I get condensation in my van even with insulation?

Insulation helps but does not stop condensation on its own. If any bare metal is left exposed, or your windows are single-glazed, those cold surfaces still collect water. You also need ventilation to remove the moisture you generate by breathing and cooking. Insulation, covered metal, and airflow work together, not separately.

Is a vapour barrier necessary in a van conversion?

Not always, and a badly fitted one does more harm than good. A vapour barrier only works if it is sealed perfectly on the warm side of the insulation. Any gap traps moisture against the metal and encourages mould. In a well-ventilated van, breathable insulation like sheep's wool without a barrier is simpler and more forgiving.

Does heating a campervan reduce condensation?

Not by itself. Warm air holds more moisture, so heating a sealed van without ventilation actually increases the water in the air, which then condenses on cold windows. Heating combined with airflow is what keeps a van dry. Run a heater and a fan together, not a heater alone.

How do I get rid of mould caused by condensation in my van?

Clean the affected area with an anti-mould spray or a diluted vinegar solution, dry it fully, then fix the cause so it does not come back. Mould means a cold surface stayed wet for too long, so add ventilation, cover the cold metal nearby, and keep wet items off soft furnishings. Treating the spots without fixing the airflow just delays the next outbreak.

Why is condensation worse in winter?

Cold weather widens the gap between your warm, humid cabin air and the cold surfaces of the van, so water condenses more readily. You also tend to seal everything up and run a heater, which traps moisture inside. The fix is the same year-round but matters most in winter: keep a small amount of air moving even when it is cold outside.