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In answering this question I tossed out that a candle lantern can add as much as 10 degrees (F) of heat while winter camping. I've heard this tossed about before, but is it true? I assume there are differences between snow-caves (well insulated) and tents (less so)... Anyone have any cold hard numbers?

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And you know, we could ask MythBusters to test this, but I wouldn't want to lose my tent in the explosion. :) It would be a simple experiment, though, so I'm inclined to make it a weekend project, or maybe over Christmas break. –  Don Branson Dec 18 '12 at 2:00
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@DonBranson That would be awesome. I love charts, graphs, and repeatable scientific results ;) - Oh, and welcome to Outdoors.SE. –  LBell Dec 18 '12 at 2:09
    
Thanks, it's good to be here. :) –  Don Branson Dec 18 '12 at 2:10
    
In short: it may provide a little heat, but you do not want to depend on it for survival. –  theJollySin Dec 21 '12 at 0:32
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2 Answers 2

Getting 10°F temperature rise from a candle in even the smallest of tents is clearly nonsense. Do the math.

Figure a candle puts out about 80 W. Of course there is large variation from candle to candle, but this is in the reasonable range for a typical modern paraffin candle. Let's say 100 W to be generous.

Next we need to come up with the surface area over which this supposed 10°F difference will dissipate accross. About the smallest you could call a "tent" would need to be long enough for a person to lie down in with some extra room sideways and at the head and toes. Let's say the footprint is 8x3 feet. That's "small" by most standards. Let's also say the bottom is insulated. That means the 100 W is dissipated over at least 24 square feet just due to the footprint alone. Obviously the height of the tent will add some to that. Again, let's be generous and say the surface area of concern is only 25 square feet. That's very small.

Dissipating 100 W over 25 square feet means 4 watts per square foot, or 13.7 BTU/h per square foot. At a insulation "R value" of 1, 13.7 BTU/h per square foot would cause a 13.7°F rise. That means the tent fabric would need to have a R value of 0.73 to sustain the 10°F rise at that same power level. Not gonna happen. To put this in perspective, a 1/2 inch of plywood has a R value of 0.63, and 1/2 drywall of 0.45. Do you really think a few mils of nylon are going to insulate better than a 1/2 inch of plywood?

And this is just looking at the conductive heat losses thru the tent wall fabric. Of course there will be some ventillation, so a considerable fraction of the heat power will be lost by convection. And, these were all quite conservative numbers, especially considering we'd be talking about a 4-season tent when this would matter, and those tend to be physicaly larger. Even taking the conservative 3x8 foot footprint and adding a side wall just 3 feet tall all around adds 66 square feet. 90 square feet of surface area would still be a small tent. Consider that is equivalent to a 9.5 x 9.5 foot sheet of fabric.

The point of the ultra-conservative numbers was to show that it's not even close with that, so the 10°F rise from a candle in any real winter tent is totally absurd.

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To add, that if the 10°/candle was true, it wouldn't take many candles to heat a tent up to nearly room temperature, but it shouldn't be too hard to realize that won't happen. –  whatsisname Dec 19 '12 at 5:20
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Ahh, but Snow is indeed a much better insulator as the OP wondered in the question. en.wikipedia.org/wiki/R-value_(insulation) notes that it is R-1 which would make the numbers quite a bit different. –  sdg Jan 6 '13 at 2:06
    
@sgd: Saying snow has any particular R value makes no sense. Perhaps some particular type of snow at a particular depth may have a reasonably repeatable R value, but just "snow" doesn't. In any case, for this snow to matter in the analisys above, it would have to cover the tent. A tent covered in snow would be better insulated than one that is not, but only for temperatures below freezing. Snow is essentially a infinite heat sink at its melting point. –  Olin Lathrop Jan 6 '13 at 20:02
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@OlinLathrop I was picking up on the original question, asking about show caves. Indeed they can be warmed quite a bit from a single candle or even just radiated body heat. –  sdg Jan 6 '13 at 21:34
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There are several issues here just in the first part. 8x4 is hardly as small as it gets for reasonable tent size (not even close). Also, 8x4 is 32 sq ft, not 24. Considering that your argument is "do the math" and there are significant errors with your numbers right from the start, I have doubts as to the validity of your conclusion. –  Russell Steen Jan 9 '13 at 17:03
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I've gone winter camping several times, usually staying in a tent, and I prefer to avoid candles in a tent so have no data about that. However, on one long-weekend trip I stayed in an igloo built from blocks of snow, north of Grand Rapids MN. After the four of us on the trip skied far enough into Suomi Hills (see map) to be well away from roads and trails, we tramped down an area of snow on a lake, then after a few hours cut out snow blocks and built an igloo, about 10 feet across outside and a bit less than six feet high inside. After it was done, I left a small candle-lantern burning inside while we fixed dinner outside. By itself the candle warmed up the air in the igloo to 40°F, which I would count as about 8°F of warming, supposing the inside surface of the igloo to be about 32°F. The small entrance to the igloo was covered much of the time. The air in the igloo warmed up to 50°F with all of us in it, while outside air temp varied from 24°F down to -12°F.

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