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A recent answer said:

In an emergency a tea light candle carefully set on/in a disposable pie tin can heat a 4 season tent enough to aid the drying process - just be sure to isolate, ventalate, and insulate the flame properly! -- (tent model, size, wind, temp, and humidity will all change effectiveness)

A tea light does not have a lot of fuel, and if you consider food that a person eats as fuel, it would seem that a person burns a lot more fuel then a tea light. By extension if you have a person and tea light in the same enclosed area it would seem that the majority of heat being generated would come from the person. Keep in mind that both the person and the candle are combing (burning) Carbon and Oxygen, both include a supply of Carbon, but require Oxygen to be replenished from the environment.

I googled around a bit, and did not find an authoritative answer, but it seems like most hits are listing a resting human body as 100 watts of energy and tea light as 30 watts of energy. I have personally used a 60 watt incandescent light bulb as a heat source, and in a small area it is significant. It does not require ventilation, but is a fire hazard.

To answer the question: Can a tea light candle safely generate useful amounts of heat? I think there are couple of points that need to be addressed.

  • What is the heat/energy output of a person?
  • What is the heat/energy output of a tea light?
  • Do both consume similar amounts of Oxygen for the amount of heat/energy given?
  • If we assume a two person tent provides sufficient gas exchange for two people, can an equivalent number of tea light candles provide the same heat/energy without additional ventilation?
  • The candle also makes a fair bit of water vapour which isn't conducive to drying. – Chris H Feb 1 '18 at 17:20
  • @ChrisH Per It takes 9,274 BTU to evaporate 1 gal. of water from 70. F. combined with the answer by charles it would take about 35 candles burning for an hour to evaporate a gallon of water. – James Jenkins Feb 1 '18 at 17:41
  • what's evaporation got to do anything? When hydrocarbons (like paraffin wax) burn, they react with oxygen from the air to make carbon dioxide and water. I can't really run the numbers on mobile without even pen and paper, but I'd expect several times the mass of the candle. – Chris H Feb 1 '18 at 17:48
  • @ChrisH So you are saying burning the candle would generate water vapor, making the air more humid, at the very least slowing drying/evaporation, but possibly adding more moisture then it removes from an object in a confined space?. – James Jenkins Feb 1 '18 at 18:00
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    exactly. I've done some quick calculations. Very roughly, the reaction would produce about twice the weight of the candle in water vapour. A typical tea light is around 10g so we'd produce nearly 20g of water from that. That's enough to take the humidity of a cubic metre of completely (and unrealistically) dry air up to 100% (i.e. condensing) at 15C. Balancing this with the required ventilation would be tricky. – Chris H Feb 1 '18 at 18:04
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TLDR: Two candles to a person but you really shouldn't have an open flame inside a tent.

BTU of a person,

Based on a 2,000-calorie diet, the human body generates about 330 BTUs per hour of heat.

...

This number fluctuates depending on the conscious state of the person. For example, a human body may give off closer to 400 BTUs of body heat while active but only 315 BTUs or fewer while sleeping.

Source

BTU of a candle

"Now, how many candle do we need to produce 10 kBTU/h? It turns out that the energy output of candles is well studied:

From measurements of the mean mass loss rate (0.105 g/min) and hceff (43.8 kJ/g), the steady-state heat release rate from the candle was calculated as 77±9 W"

Which can be converted to be 263 BTU/h.

Source

So two candles would produce more heat than one person.

As regards the oxygen, using an open flame inside a tent is a BAD IDEA partly because you can set the tent on fire, and partly because of the risk of carbon monoxide poisoning.

Never use an open flame inside a tent. This includes any type of fuel-burning lantern, candles, stove or grill. Use only battery-operated lights.

Source

Never use a flame or any other heating device inside a tent.

Source

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