Hi Jack, good quality diesel heaters like the dometic one are safe, their intake and exhaust are outside, only air over the head fins heats the van. fitted probably 100 of them now, I don’t like the gas ones by truma, exhaust and inlet are inside and prone to leaking if installed poorly. They do cut off f intake breathes fumes from exhaust inside the intake tube. Cheap Chinese copies should be avoided, they are poorly done with no safety features. One customers read 190c on the heating outlet when I tested out of curiosity last week. That will melt clothes, shoes etc, and burn you if not careful.