Ventilation is an essential part of any van build.
It is often hotter inside the van than outside. Heat comes from several sources:
When it is hotter inside than outside the vehicle can be cooled by pulling outside air through the van. The fan cannot lower the van's internal temps lower than the outside temp.
Humidity is a serious concern for people living in sealed metal boxes. It can cause mold, mildew, and discomfort.
Humidity can come from:
Up to 28% of the fluids you take in will be released into the air through skin or lungs.2)
Ventilating with lower-humidity air from outside can help control humidity.
Cooking, smoking, or vaping inside releases particles that can be reduced by ventilating.
Unpleasant smells can be reduced by ventilating
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.