I would go propane for ease of installation. It burns pretty clean ( a lot depends on the supplier) and ease of installation. B vent is the same as hot water heater venting, inexpensive and easy to shoot out the roof. If you went direct vent it would be enclosed and there would be no problems of any contaminants. A heater hanging from the ceiling works well, puts out a LOT of heat in a short time.
"When I was younger, I could remember anything, whether it had happened or not." - Mark Twain