In a previous blog post we looked at building a cooling device made with clay flowerpots. Clay is a versatile natural material which has been put to use in hundreds of various ways for thousands of years. Today we will consider the ‘pot-in-pot’ space heater.
Does it work?
Let’s see what kind of performance we can expect from a pot-in-pot space heater. A typical $0.10 tea light burns for 4 hours and has the following dimensions:
This is equivalent to about 18.85 cubic centimeters (cc).
We know from the tables that paraffin wax has a density of 0.93 g/cc
Therefore, we calculate the mass of paraffin in the candle as:
Heat of combustion for paraffin is 42kJ/g so we determine that the energy produced over a 4 hour time period is:
Yes, 51.1 J/s is a mere 51.1 W. Now, as most published videos on these heaters call for using 4 tea candles at a time, you are looking at a tiny 200 Watt (400 W as configured in the video) space heater with potential carbon monoxide issues… not to mention the hazards of having open flames in your home. Definitely not the kind of thing to have with children and/or pets around the house.
The design shown in the video above appears to be much safer than many of the others you can find online. In an emergency I’m sure it’s worth the risk in order to save a life but, as for a day to day source of warmth?, I wouldn’t recommend it. Even if the fuel cost is less than $5 per day, without adequate ventilation and additional safety precautions this can be a very dangerous device and the actual cost could be tragically higher in the end.