Ventilation is an essential part of any nomadic vehicle; when living in a vehicle you cannot keep everything sealed up tight, even in very hot or cold weather. Ventilation is needed primarily for humidity control, but also for fresh air, to reduce odors, and for temperature control. Humidity is an ever-present consideration for people who live in vehicles. Excess water vapor and condensation can cause mold and mildew, and it can discomfort in warm or hot weather.
Ventilation for humidity control
Ventilating with lower-humidity air from outside can help control humidity. In addition to the outdoor humidity levels from the local weather, some of the humidity in your vehicle comes from humans and pets; one human (at rest) adds up to 20ml of water to the air every hour from their breath (respiration), which may total ⅓ to ½ of a liter or quart per day.[1] More water is added to the air through the evaporation of visible sweat (perspiration) and invisible evaporation from the skin. Up to 28% of the fluids you take in (from water, food, etc.) will be released into the air through skin or lungs.[2] Additional humans or pets each add more water vapor to the air.
The rest of the humidity comes from liquids in your vehicle that turn to gases: cooking, especially when boiling or simmering liquids, releases a great deal of water vapor into the air. Evaporation of other liquids, such as those used for in-vehicle showers, cleaning, spills, wet laundry, and leaks from water tanks.
Ventilation for keeping cool
When it is hotter inside your vehicle than it is outside (the ambient temperature), you can cool your vehicle down by pulling outside air through the van with a powered vent fan or by opening windows and doors to take advantage of the breeze. Without air conditioning or other methods of keeping cool, you cannot lower your vehicle's internal temps lower than the outside temp.
Ventilation for odor control
Smells from toilets, garbage, dirty laundry and shoes, and body odors from humans and pets will all contribute to unpleasant smells. Cooking, smoking, or vaping inside releases particles that can be reduced by ventilating. See Reducing odors in your vehicle.
Effective ventilation
Ventilation requires air entering and exiting the vehicle. Running a fan in a closed vehicle is not ventilation. Running a nice roof vent without some way for air to enter the van accomplishes little.
Location of the air entrance/exit is critical for cross-ventilation (moving air throughout the van). Cracking a window near the roof vent does little for areas further away in the van. For best results, place the main vent at one end and the passive intake (or second vent) at the other end.
