Technical
Ventilation: the half of good insulation almost nobody mentions
Two people breathe out about a litre of water a night, and cooking and showering add more. Insulation keeps the warmth in; ventilation gets the moisture out. Get the second right and you wake up in November in a dry van with dry windows — it takes two openings and one habit.
Updated on 9 min read
Why two openings, not one
Air going out has to come from somewhere. One open roof vent therefore does far less than a low opening plus a high one: warm, humid air rises and leaves at the top, while cool dry air comes in below. That happens by itself, without a fan and without power, as long as you have both openings.
- Low: a grille in the floor or in the bottom of a door, or a sliding door that can sit ajar.
- High: a roof vent, preferably as far from the low opening as possible, so the air travels through the whole van.
- Above the hob is the third place worth having: cooking on gas puts roughly a litre of water into the air for every litre on the stove.
Three habits that do the most
- 01
Roof vent a centimetre open, also in winter
It feels odd when it is freezing outside, but it costs only a couple of degrees and takes the overnight moisture peak away. A vent with a detent makes this easy to keep up.
- 02
Five minutes of through-draught after cooking and showering
Door and vent both open. In five minutes the moisture peak is gone while the warmth is still in your furniture, which gives it back afterwards.
- 03
Air under your mattress
The coldest and dampest place in the whole camper is the underside of your mattress, where body heat meets a cold base. A spacer mat or a slatted base lets air pass, and your mattress stays dry. This is the cheapest measure in the article and immediately the most noticeable.
If you still notice damp in spring and autumn, a small heater that moves air is the most effective answer: warm air carries more water and takes it out through your vent. An electric dehumidifier does the same, but draws power you would usually rather spend elsewhere when off-grid.
Read how to insulate without condensation
What you need for this
We do not (yet) sell these parts separately. The list is here because this is what should be in your basket before you start.
- 40 × 40 cm roof vent with detents and a flyscreen
- Ventilation grille for low in a door or the floor
- Spacer mat or slatted base under the mattress
- A hygrometer, so you do not have to guess
Frequently asked questions
- How do I prevent condensation in my camper?
- With two openings and three habits. Provide a low inlet and a high roof vent, so humid air leaves at the top by itself. Leave the vent a centimetre open at night too, air the van through for five minutes after cooking and showering, and put a spacer mat under your mattress. That last one is the cheapest measure and immediately the most noticeable.
- Should the roof vent stay open in winter?
- A centimetre, yes. It costs only a couple of degrees and removes the overnight moisture peak, keeping your windows and the underside of your mattress dry. A vent with detents makes that easy to keep up.
- Why is the underside of my mattress wet?
- Because your body heat meets a cold base there and the moisture from your sleep has nowhere to go. The answer is air: put a spacer mat or a slatted base under the mattress so ventilation runs along the underside. Also avoid placing the bed directly against an uninsulated outer wall.