Thursday, December 12, 2013

Heating a room for 8p a day with tea lights YouTube video analysis

This video was recently brought to my attention: 

My first thoughts were:

  • Oh god, another free energy / perpetual motion machine idea
  • Hmm: this guy seems to understand basic energy (given his observation that the computer contributed to the room heat budget)
  • He works for a boating magazine (those guys tend to know their basic science/math).
So looked I at the figures.

It seems he's taking about these tea lights:

They're actually €2 here in Ireland (about 1.70 GBP).

Measuring some tea lights I have here (they can't be too different to those IKEA candles), the diameter is 39mm x 11mm high. That's a total volume of 1.314 litres of wax for all 100 tea lights. It's most likely parafin wax in those candles. The density of parafin wax is 900kg/m3 so that's 1.183kg of parafin wax.

Looking at the heat of combustion per unit mass  parafin wax and kerosene / heating oil are pretty much identical energy wise at 46MJ/kg [1]. So the tea lights represent 54MJ of energy [2].

Looking at the latest prices for heating oil (kerosene) in Ireland (December 2013) is €0.83/litre. The density of kerosene is slightly less than parafin wax at about 800kg/m3. So to get 54MJ of energy I'll need 1.479 litres of kerosene. That's €1.22 at current prices.

Which is almost identical to 1 GBP at the time of writing. So fuel wise, this is on par with home heating oil (at the time of writing).

So what's with the flower pots? From a basic physics point of view there is no energy advantage here that I can see. But what it does do is contain the flame and make the apparatus safer than naked flame.


Tea light candles are handy, store well and don't spill. They are also (probably) safer than liquid kerosene. At 1 GBP it's on parity with home heating oil for energy/cost. At the €2 price it's not quite as efficient as heating oil, but still in the same ball park. There might be a CO risk for small poorly ventilated spaces... but I guess no different to that of candles. Ok.. there might be something to this after all.. but it's no energy miracle.


[2] Burning stuff is a rather efficient way of releasing energy. You'll get pretty much every scrap of that in heat.