Within the last two weeks, I read something that said a single candle puts out about the same BTU as an inactive adult. I don't remember if it was sleeping or awake and just laying there.

It said that in an emergency, if you were alone or with an insuficient amount of people, in a small enough space where body heat could make a significant difference, you could use a candle or two to heat the area, providing they were used in a safe manner (such as placeing the candle inside a cleaned and vented soda can) and with adequate ventilation.