Passive Ventilation

Almost all van conversions include some kind of a roof fan for ventilation.. However, the effectiveness of such a fan is sometimes quite low, since for the good ventilation the air pushed out of van by the fan should be replaced with the same amount of fresh air from outside. Thus there is a need for openings, preferably at different locations to have nice air flow through the van.  Such openings, thoughtfully positioned also may provide for the passive ventilation even when fan is off, but is opened.

Typically, screened opening windows serve this purpose. In my van I have only one window that opens and have a screen - rear driver side that has two openings: in bathroom and bedroom. Thus there is essentially no air flow in the front and middle of the van (with the fan off or on), which makes the van interior hotter than it could be.

To correct the problem, I decided to make additional openings.  For the location I chose the bottom of the footstep wells by the front doors. The benefits of such location are:
1. The openings at the bottom suck the coolest air around, which is typically under the van;
2. The openings at the very front creates the best ventilation flow through the whole van;
3. It is relatively easy to do holes there without making any changes to the existing layout, and not having to drill through multiple floor layers.
4. No obstacles at the van bottom like fuel tank, exhaust pipe, frame elements, etc.

Pictures and description below show the design and fabrication the those  vents.

First, I removed the plastic casing from the the footstep wells and calculated the possible position and size of the openings. Based on the available space and what can be found in stores, I chose the 4" round holes paired with the 4" drier exhaust plastic hood vent cap from Lowe's, of which I used only plastic part without connecting pipe.

Then I cut the round hole in the metal floor and screwed the hood to the floor underneath it (some cutting of the hood base was needed to fit the tight space under the floor)

Since the footstep well space was opened, I decided to insulate it putting 1/2 inch insulation around.
I also glued the mosquito screen to the cap grille.

  

Then I traced the hole position to the plastic casing and cut a hole there. However, I did not cut it completely. The part of the hole adjacent to the vertical wall I did not touch. This black plastic is relatively flexible, so the cut piece can flex, and serve as a cap that can be kept opened or closed by adding little locks on the floor and the wall.

 

This feature is important not only for the colder time of the year when opening is not needed,  but also to keep noise away when driving, because with open cap it is really loud. I keep the caps open all the time when not driving,  and with opened MaxxAire fan it  makes the air in the van little bit cooler and fresher.

After finishing the job, and testing it, I realized that if I opted for the self made hood instead of buying it, I probably could make the ventilation even better by making a larger rectangular  4x8" opening.  But it's too late now.