Charcoal give off Carbon Monoxide. Never burn it in enclosed places!
The warning about charcoal and enclosed places is from the charcoal using the available oxygen to initially produce carbon dioxide and then producing both gases as the available oxygen is depleted. His description of a air leaky building leads me to believe that it would not occur here.
Sorry about the double post earlier.
Test it with a carbon monoxide detector.
Good point about CO and will it harm plants. My parents ran a greenhouse for years. They communicated with other green house operators often. They never heard of someone killing their plants with carbon monoxide. They heated with coal with a very old furnace so the opportunity would have arisen.
The lead singer from Boston knew about this fact and used it to commit suicide by lighting a charcoal burner in his bathroom.