Campervan ventilation: a fan is not the same as ventilation

Ask a builder about ventilation and you get a fan: brand, blade count, whether the reversing function is worth it. That is a good conversation about a different subject. A MaxxFan is forced ventilation — it works when you switch it on, when the battery has charge, and when you are awake enough to think about it. What EN 721 asks for is permanent ventilation: fixed, unclosable openings sized by floor area that keep working with the fan off, the doors shut, the heater running and everybody asleep. That is precisely the state in which people get hurt, so that is the state the standard is written for.

The architecture is simple and has not changed in decades. High openings let warm, moist air and any combustion products out, because that is where they go on their own. Low openings let replacement air in, near the floor, where cold dense air arrives. Two holes, one pressure loop, no electricity involved. A fan sits on top of that system; it does not replace it.

What EN 721:2019 actually asks for

The requirement scales with the habitation floor area — the plan area of the living compartment, not the exterior footprint of the van. For compartments containing a non-room-sealed appliance (a gas hob, a flueless heater, anything that burns fuel using cabin air), Table 1 gives these minimum free areas:

Put that in van terms. A long-wheelbase panel van has roughly 6–7 m² of habitation floor, so it lands in the 5–10 m² band: 10,000 mm² high and 1,500 mm² low. Ten thousand square millimetres sounds enormous until you convert it — it is a circle of about 113 mm diameter, or a square roughly 100 × 100 mm. The low-level figure is a 44 mm circle. These are not heroic openings. They are two modest holes that most builds simply never cut.

The rule almost everyone misses: wall vents count half

A high-level opening that is not a roof vent is credited at only half its free area, because a vent in a side wall drives a far weaker stack effect than one at the top of the box. The practical consequence is blunt: a wall vent must be twice the area. That 6.5 m² van needs 10,000 mm² through a roof vent — or 20,000 mm² if the high-level opening is a mushroom in the side panel. A 12 m² coachbuilt goes from 12,500 mm² to 25,000 mm². This is the single cheapest reason to plan a roof opening early rather than improvise a wall vent late.

Position is prescribed too, and the numbers are the ones inspectors reach for first. A wall-mounted high vent must sit at least 1800 mm above the floor and at least 300 mm above the highest mattress, measured uncompressed. Low vents must be within 100 mm of the floor. In a van with a 1900 mm internal height and a fixed bed at 1100 mm, that 1800 mm line runs through the top of your overhead lockers — which is exactly why this belongs in the layout stage and not the trim stage.

No open flame, smaller holes

If the compartment contains no open-flame appliance at all — induction hob, diesel heater with a sealed combustion circuit, no gas anywhere — the requirement drops sharply:

The halving rule still applies, so a wall vent in a small all-electric van is 3,000 mm² rather than 1,500 mm². Note what this table is really telling you: going gas-free does not remove the need for permanent ventilation, it just shrinks it. The moisture is still there, and so are you.

“Free area” is a layout constraint, not a plumbing one

Free area means unobstructed area — the actual open path through the vent, after the grille, the flyscreen and the louvre have taken their cut. A 100 mm duct behind a decorative plate with 40% open area does not give you 7,850 mm²; it gives you about 3,100 mm². Manufacturers publish the free area of their vents. Use their number, not the hole diameter.

And then keep it free. A low vent behind the galley plinth stops existing the moment you slide a crate of tools in front of it. A high vent covered by a blackout curtain at night is closed during the exact eight hours it was specified for. Cushions, wardrobe contents, towels drying over a locker door, a bike wheel in the garage — every one of these is a permanent vent turned into an occasional one. This is why ventilation is a decision you make with the furniture plan open, alongside the order you build things in, and not a job you bolt on after the panels are screwed down.

The physics: you are producing litres of water a day

Two sleeping adults each release roughly 40 g of water vapour per hour, and considerably more once they are awake and moving. Cooking a meal adds about 250 mL. An unvented propane burner adds roughly 450 mL per hour per 10,000 BTU — burning hydrocarbons produces water, and it all ends up in your air. Add it up over a winter day and a couple in a van is putting 1–3 litres of water into a sealed metal box.

Without a path out, that water does not stay airborne. It migrates to the coldest surface it can find, which is the sheet steel behind your beautiful cedar panels, and it condenses there. You will not see it. You will smell it about eighteen months later. Mould in the insulation, rot in the ply, and rust working outward from the inside of a panel you cannot inspect without dismantling the build. A dehumidifier does not fix this; it treats the symptom in the air you can reach. Permanent openings fix it by giving the moisture somewhere to go all night, every night, at zero amps.

The safety half: combustion air and CO

The moisture case is about your van. The other case is about you. Any flueless combustion — a gas hob, a catalytic heater, a badly installed water heater — consumes oxygen from the cabin and produces carbon monoxide when it cannot get enough. The permanent low-level opening is what feeds the appliance its combustion air. That is its primary job; ventilation is the secondary one. Block it with a storage box and you have quietly converted a safe appliance into an unsafe one, and the failure mode is invisible, odourless and happens while you sleep.

Fit a carbon monoxide alarm to EN 50291-2 — the part of the standard written for vehicles, boats and caravans rather than houses, because it accounts for vibration and temperature swing. Inspectors expect to see one, buyers ask about it, and it costs less than a length of tongue-and-groove. It is not a substitute for the vents; it is the alarm that tells you the vents have been defeated.

Who checks, and when

In France, VASP homologation is where this becomes concrete. The gas and habitation checks (Qualigaz, then DREAL) look for the ventilation openings even when no gas appliance is fitted — a fact that surprises people who assumed an all-electric build sidestepped the subject. German TÜV assessors work to the same family of standards for the habitation side. Both are far easier to pass at the drawing stage than after a full fit-out, because retrofitting a roof vent through a finished ceiling means pulling the ceiling. It is the same calculation as deciding on a wet room: cheap as a decision, expensive as a change of mind.

Design the holes before you design the cabinets

Permanent ventilation is two openings, correctly sized, correctly placed, and kept clear for the life of the van. It costs a roof vent and a floor grille. It is checked by inspectors, it decides whether your insulation survives, and it is the difference between a gas hob being safe and being a hazard.

The useful move is to make it a number you can see. VanPlot already knows your habitation floor area and where you have placed openings, so it can hold the required free area against what you have actually installed and flag the shortfall — including the doubling when your high vent is in a wall rather than the roof. If you want to check a build you have already drawn elsewhere, the free campervan ventilation calculator runs the same EN 721 table in your browser, no account needed.