Robocop,
For fear of starting the vented vs. non-vented debate, here is my answer.
My Portable Buddy manual says nine square inches (i.e.; 3" x 3").
(Note that the Canadian version is "Not approved for use in tents or RV's")
Interestingly, the Olympic Wave heater
manual, which is a lower BTU rated appliance, says 24 square inches (i.e.: 6" x 4"). Furthermore, they recommend that this be a "combination of a window AND ceiling vents" to allow natural convection to move combustion waste products out of the enclosed space. So that's a 8" wide window open 1/4" to 1/2" AND a 14" x 14" roof vent open 1/4" to 1/2". If it was me, I would go with this ventilation, or more, for the Portable Buddy heater.
Hope this helps,
Steve
