Ventilation calculator (EN 721)
Fixed ventilation is not the same thing as a fan you switch on. EN 721 asks for permanent openings — high to let warm, moist air and combustion products out, low to let replacement air in — sized by habitation floor area.
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Required high-level free area
10000 mm²
Required low-level free area
1500 mm²
Wall high vents must sit at least 1,800 mm above the floor and 300 mm above the highest mattress. Low vents go within 100 mm of the floor.
Free area means unobstructed: curtains, cushions and stored gear must never cover a vent.
Planning figures, not certification. Standards are summarised for builders; your inspector, your van's plate and your own measurements always win.
How this is calculated
- EN 721:2019 Table 1 sets both areas from the habitation plan area — 7,500 mm² high and 1,000 mm² low at 5 m², rising to 20,000 / 5,000 mm² above 20 m².
- A high-level opening that is not a roof vent only counts half, so the required area doubles.
- Without any open-flame appliance the requirement drops: 7,500 / 1,000 mm² above 10 m², and 1,500 / 500 mm² below it.
Sources
- EN 721:2019 — Leisure accommodation vehicles: safety ventilation requirements
- EN 1646-1 — Motor caravans: habitation requirements
- Qualigaz / DREAL VASP inspection practice (France)
Questions builders ask
How much ventilation does a campervan need?
EN 721 sets it from habitation floor area, not van size. With an open-flame appliance fitted the requirement runs from 7,500 mm² of high-level free area plus 1,000 mm² low at 5 m², up to 20,000 / 5,000 mm² above 20 m². Free area means unobstructed — curtains, cushions and stored gear must never cover a vent.
Does a roof fan count as campervan ventilation?
No. EN 721 asks for permanent openings that work with nothing switched on and nothing closed, so a powered fan or a hatch you can shut is extra airflow rather than the required free area. You still need fixed high and low vents, with the low one within 100 mm of the floor.
Why does a wall vent need twice the area of a roof vent?
Warm, moist air and combustion products collect at the highest point, and a vent in a wall sits below that — so EN 721 counts it as half as effective and the required area doubles. A wall high vent must also sit at least 1,800 mm above the floor and 300 mm above the highest mattress.
Keep reading
Plan the whole van, not just this number
VanPlot is a 3D layout planner for camper conversions. Place real components in your real van and watch weight, axle loads, power and cost update live — this calculator is one panel of it.
Who makes this
I'm Vladimir. I'm planning my own conversion, and none of the tools I tried could tell me whether a layout would fit or what it would do to the rear axle, so I made this one. I work on it alone. If something's wrong or missing, write to me — the address goes to my inbox.
Vladimir Šterjoski