The results of too little oxygen or too much exhaust gas in the room are obvious. I grew tired of worrying about whether I had opened enough windows. After a couple of miscalculations and getting sick, I removed the heater. In a large room with high ceilings, these problems are probably minimal. This results in less fumes escaping into the room, but it is hardly completely effective.
Combustion still occurs in the room and uses up oxygen.
The need for vigilance in maintaining proper ventilation still exists. Yes, the plans are on the drawing board. An automotive type heater core is certainly only one of several possibilities for the heat exchanger unit. For the 140 square feet of space to be heated in my trailer, it worked perfectly. For larger spaces, the coils out of an old refrigerator would seem to be a good candidate.