Van and motorhome ventilation: how to breathe without ending up with mould

Did you know that you exhale up to two litres of water per night? That moisture doesn’t evaporate by magic. In a flat, you never see it. In a 6 m² van, it lands straight on the first cold surface it finds, and in the morning you wake up with condensation everywhere (for us, it was the windscreen, I’ll get back to that).

Honestly, at first we all thought ventilation was just a summer thing, to stop yourself cooking. But the real danger is in winter, lurking in the condensation, and it works away while you sleep. That’s why this slightly thankless topic deserves a proper look, whether you drive a self-built van or a factory motorhome (spoiler: the motorhome isn’t spared, it’s just better kitted out from the start).

Why ventilation is vital, summer and winter

The sneaky damp of winter

It’s the enemy you don’t see coming. Your warm, moisture-laden air (your breath, your cooking, your shower) meets a cold surface and, bam, it turns into droplets. In our Édouard, our Hymer B544, the pop-top bed sits right above the cab, so against the biggest window in the vehicle: the windscreen. The upshot, on winter mornings, was waking up to a proper little pond of condensation on the glass. Imagine what that does to the rest, on wood or fabric that won’t dry off with a quick wipe.

And this is where it gets serious: above 70% humidity, mould takes around 48 hours to colonise a wall. It isn’t just about a smell or a van ageing badly; the WHO links a significant share of asthma cases to indoor mould. In short, we’re not talking décor, we’re talking about your lungs.

In summer, the heat and the gas you forget

In summer, the overheated air stalls under the roof and quickly climbs past 40 degrees. Unpleasant, but not the worst of it. The real risk is the gas from your hob: with no air renewal, carbon monoxide builds up, and you won’t feel it coming. Proper ventilation isn’t a comfort feature; it’s what stops a daft accident.

Beyond that, managing a heatwave is a whole job in itself (fans, blackout, air-con, orientation). We put together a full guide just on that in our article on beating the heat in vanlife, so here I’ll stick to background ventilation.

How air actually circulates (two principles, zero electricity)

No need for an £800 system. Just two laws of physics you already know without realising it: warm air rises, cool air sinks, and it all follows from there. The first plays on height (the chimney effect), the second on width (cross ventilation). A little diagram beats a long speech.

In practice, the chimney effect works even while you sleep: give it an exit up top and an inlet down low, and it does the rest. Cross ventilation is the one that saves you when you’re parked up on a hot day: two opposite windows, a bit of wind, and you get an instant through-draught. Our summer reflex is to point the van so the side window catches the wind and open the opposite rooflight.

Low and high vents: good practice (and the gas-safety point)

Here’s the good news for the UK: there’s no habitation inspection to pass, so on paper a private conversion isn’t forced to carry any particular vent. That’s exactly the trap: the moment you fit a gas hob or a heater, fixed low and high ventilation stops being optional. It’s the gas-safety standard, and it’s what a Gas Safe engineer checks if you ever want a habitation gas certificate (increasingly asked for by insurers and some campsites).

How much vent area, in practice

The figures everyone works to come from BS EN 1949, the standard for LPG installations in leisure vehicles. It sets permanent ventilation (meaning: that can’t be blocked) sized to the space and to any gas appliance. In short:

• Low vent: less than 10 cm from the floor, to clear the heavy, damp air.
• High vent: high on the wall or straight through the roof.
• With a gas hob on board, add dedicated vents for the gas locker (reckon around 100 cm² of high ventilation for a 6 m² van).
• These vents stay open permanently: a vent you can close, as far as safety goes, doesn’t count.

Reclassifying the van as a “motor caravan” with the DVLA is a separate matter (it hangs on windows, seating and layout, not on vents), and GOV.UK spells out the criteria if you go down that route.

Ventilating without drilling the bodywork (yes, it’s doable)

This is THE question that nags when you’re converting the van yourself: do I have to cut a hole in my lovely panels? Not necessarily. The best-known trick is to fit the low vent on the sliding door, at step level. Fresh air comes in low, flows towards the chassis, and you’ve no visible grille cutting into your bodywork. For the high vent, an existing rooflight already does the job. The moral: in plenty of cases you can be sorted without ever reaching for the hole saw.

Which passive ventilation solution to choose

Enough theory, let’s get to the kit. Here are the passive options, from the plain window to the wind-driven extractor, with what each is really worth.

On a motorhome, windows and rooflights are there from the start; on a self-built van, the choice is yours. A mushroom vent stays usable even in the rain but lets in less air than a lift-up model. The newer versions also give you a constant airflow, precisely because the cabin is small and a gas leak is unforgiving.

For background renewal, nothing beats the pairing of a low grille plus a high extractor. A wall or floor grille gives you permanent ventilation for a laughable price. And if you want to boost extraction without a scrap of electricity, the wind-driven roof extractor spins on its own the moment there’s a breeze. It’s simple, it’s bombproof, and it works for you around the clock.

Beating damp for good: keeping a van genuinely healthy

Ventilating is half the battle. The other half is stopping moisture settling in the first place.

Insulation, your first line of ventilation

It sounds counter-intuitive, but the best anti-condensation weapon is good insulation. The logic is simple: the closer your walls sit to the indoor air temperature, the less cold surface there is for water to condense on. We learned it the hard way, funnily enough. Our first winter in the Algarve, we rented a stone house and left Édouard in the car park. Well, we were colder and damper in the house (15 degrees, no air movement, walls built for summer) than in the van out in the sun. I ended up asking the local owners, and finally understood why the shops around here are stacked with dehumidifiers.

Moisture absorbers and everyday habits

On top of that, a simple moisture absorber (the refillable salt tub, a few pounds) works wonders in small spaces, especially when you’re parked several days in the same spot. Then there are the free habits: cooking outside in the evening when you can, wiping the morning condensation off with a microfibre cloth, not drying three loads of washing with the doors shut, and easing an adjustable vent partway in a bitter draught rather than sealing everything up. The idea is to help the air do its job, not to trap it.

PS: for us, the day we twigged that the soaking windscreen each morning wasn’t fate but simply an airflow problem, Édouard stopped weeping at wake-up. You’ll get there too. Open the right vents, in the right places, and let physics do the graft.