I have seen this method used to heat small spaces without using natural gas, propane or electricity. A 3 pound can of vegetable shortening can burn for 8 hours a day for over a month. It seems to be a relatively safe method to generate heat in an emergency situation. All you need is a couple of terra cotta pots, 2 heating ducks, 2 small jars, 2 birthday candles, and a can of vegetable shortening.