Calculating the efficiency of my candle

 

I took some results for my candle water-heater and I tried to look up a value for the Joules per gram of candle wax. I found 43kJ and 37kJ so let's say 40kJ per gram. 0.28 grams of wax burned which releases about 11000J. It was set up so a 1 degree Celsius rise in temperature is worth 100J so that means 3140J of energy went into the thermal store of the water. If we are using this candle as a water heater, then the efficiency = 3140/11000 = 0.28. The rest is dissipated to the surroundings as heat and light (heating by particles and heating by radiation in the new parlance). Presumably I would get a higher efficiency if I moved the candle closer, say 2cm instead of 3 cm.