MadSci Network: Physics

Re: BTU's in one candle?

Date: Wed Jan 9 17:35:41 2002
Posted By: Jaime Valencia-Rodríguez, Guest Researcher, Chemical Science and Technology Lab, NIST.
Area of science: Physics
ID: 1009958226.Ph

Dear George:

Thank you very much for your question. In order to answer it I would like 
to start discussing the way a candle burns.
we read:

 Candle flame : A candle is made of wax made from petrochemicals. The 
wick is lighted, this melts the wax. The evaporated wax rises and catches 
fire. As the vapors rise higher, they stay longer in the hot regions of 
the flame and start burning completely with oxygen.

 The candle flame has three regions
  The inner most zone : this has wax vapors. It appears dark black. The 
vapors are not burnt and this is the least hot region of the candle. 
 The middle zone : here the wax vapors start burning. The flame appears 
yellowish because the vapors are partially burnt. The oxygen available in 
this region is not sufficient for the wax vapors to burn completely. This 
is the luminous region of the candle. The temperature here is not very 
 The outer zone: here the wax vapors have enough oxygen available from 
the air to burn completely. The flame appears blue because of complete 
burning of the wax vapors. The temperature in this region is very high.

In the other hand, in
we find an interesting school test in which the following is obtained:

Wax calorific value
8.4 kJ/g

Finally, in http://www.chemie.fu- 
we find that

1 joule = 0.0009478134 btu

So, in order to know how many BTU you could obtain from a wax candle, you 
need to know the weight in grams (remember that 1 lb= 454 g), and (if the 
wax is pure), you will multiply times 8400 and then multiply by 

I hope this helps.


Jaime Valencia

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