How many incidents have been caused by the combustion heater? I have not ever heard that using these is a danger. I agree that having one of these units on fire producing heat while flying across the country could look and seem like a hazard. But these are proven appliances and with proper maintenance and use will be fine. There are a large amount of GA aircraft that have these units and you just don't hear about planes falling out of the sky. I did a quick search on the FAA site and only found 2 incidents and one of them didn't say anything about the heater. If there are more incidents that I am not finding here please pass them on to this thread.
http://www.ntsb.gov/ntsb/brief.asp?e...22X02072&key=1