I was also wondering about those candles. They look like nothing more than a wax-filled tin and some wicks made from ordinary pipe cleaners. However, there may be more to it than that. The wax probably has a higher stearic acid content like plumber's candles, for one.

I was also curious as to how much heat a candle produces. A quick web search yields estimates between 40 and 80 watts. A person who burns 1000 kcal over 24 hours would put out about 48 watts, so adding a single burning candle to your vehicle or other shelter would be like adding another person's body heat. In theory. But then you need to allow for ventilation and worry about CO...