ELI5: How can people have fires inside igloos without them melting through the ice?

ELI5: How can people have fires inside igloos without them melting through the ice?


What happens is the rough inside later of the igloo melts a little bit at first but the super cold ice behind it which is being kept cold by the outside temperatures freezes it again in to a smooth crust. Because there's now less surface area the warm inside air is less effective at melting the surrounding ice. So basically it's a constant battle between the fire inside warming up the air and the ice and cold air keeping the structure frozen, and the achieve a balance at some point.


Should also note that the 'fire' used in an igloo isn't the big ones people associate with cookouts and camping, and even fireplaces. Just a small flame can keep a such small room at a comfortable temperature.


This. Think two candles worth of fire.


That doesn't sound like enough to warm up a person.


It (generally) isn't meant to warm you up, but rather stop the air around you from cooling you down by keeping the air warm-ish. Of course size of igloo and fire size and other factors all make a difference.


When we were in the artic for some army training, we had built igloos as outhouses so we could poop without exposing your ass to -50c winds. Having the candles stuck in the ice between your knees was key to keep the chill away from the exposed skin and bits.


Chestnuts roasting on an open fire Edit* syntax* Edit 2 guys thank you for awards, god bless


Jack frost nipping at your hole


No TP for your brown quagmire And folks dressed up like Eskimos


Everybody knows that shrinking should not come as a surprise.




Damn if I had a free award to give it would have been this comment


I LOL'd at this, thank you


Chet’s nuts roasting on an open fire


Wait, I'm presuming there's no actual toilet in the igloo. What do you do with the poop afterwards? Do you scoop it up? Is there a container and you put a lid on it?


Typically with an outhouse it's just a hole. Once it fills up you bury it and dig a new one, move the outhouse (or in their case, build a new igloo) usually just a couple feet away, to keep the shit in one general area.


Like I replied in another comment, we actually used chemical disposable toilets. [link](https://www.mec.ca/en/product/5027-310/II-Disposable-Bag-For-Solid-Waste)


Ah I missed that comment. That must have helped a fair bit


>usually just a couple feet away, to keep the shit in one general area. Yes, otherwise known as Capitol Hill


Lol this genuinely made me laugh out loud


You poop in a plastic bag inside of a bucket. It's rock hard ice-poopsicle in about 10 minutes. No smell, no mess. Winter camp 101.


We actually have folding stool/seat that we use chemical disposable toilets. [link](https://www.mec.ca/en/product/5027-310/II-Disposable-Bag-For-Solid-Waste) Since we can't leave evidence, we usually have to pack the silverfish out in our packs until we can drop off our garbage with the rear echelon.


Did they have to use the words “pleasantly moist antiseptic towelette” in that product description? 😑


That was my favorite part. I'd hate for the uncomfortably damp towelette that the competition uses.


It's a Canadian requirement *C'est une exigence canadienne*


I too, have pooped in buckets in service of Her Majesty the Queen. Luckily, we had a barrel in one of the sleds for the forbidden burritos, so we didn't have to load our packs with them. I will say, the "seat" that comes with the buckets is more annoying than anything.


I think that they dig a hole in the floor when they build the outhouse, but I'm not sure.


I think that you can just kick the f\*\*\* out of it, and watch it disinteger in a thousand pieces when you're done at -50ºC


My favorite flavor of Dip N Dots.


Don't lie and call it training... We all know you were protecting NASA's ice wall that keeps people from falling off the edge of the earth


It's actually the top-secret cold-storage for the Canadian maple syrup repository.


Not that secret unfortunately https://en.wikipedia.org/wiki/Great\_Canadian\_Maple\_Syrup\_Heist


But then wouldn't they just poop off the edge?


Can I have your car when you disappear?




More like Santa. Jesus was from the Middle East.


Santa ***H***. Claus!


By this cold, your anus can freeze. Which means it dies...


Thanks, I hate the thought of anus death.


As they say in Maine; that’ll take the slack outta yah sack.


I once went to an igloo bar when snowboarding. I think it was -5c inside but I could happily take my coat off, was a weird feeling. They also offered rooms where you sleep on a bed carved into the ice with a sleeping bag, it looked really cool.


ice and snow are excellent insulators. Body heat alone does a good job of warming up and igloo


Not wind makes a huge difference. I've been out in minus 40 without wind and it's not bad


Also, igloos are built in a way that has a raised platform for sleeping, cold air sinks the lower floor and warm air rises


Also, If you are camping in said igloo, it may help to warm it up,sure, but a big part of it is also keeping the humidity down - dry means warm in winter camping!


plus the sump for the cold air to collect in.


This person knows their igloos. Critical part of it. Lower elevation near the entrance


Also, body heat


Outside is -40. Inside is 10-15C Still need to wear clothes, warm clothes even. But you're not going to freeze to death. There's also body heat. An igloo is very well insulated.


The average adult emits about 330 BTUs of heat per hour. If you've got a few people sharing the space, that's a fair bit of warmth just by itself.


Yep, I certainly haven't been to the arctic, but have built snow forts in cold weather and it's remarkably comfortable when you're out of the wind and trapping multiple bodies worth of heat in a small space.


>trapping multiple bodies worth of heat in a small space. How many popped back up when it thawed?


None, that's what was fueling the igloo campfire


Just think if we hooked up a bunch of humans to a battery farm hmmmm.


Why bother harnessing the abundant geothermal energy lurking a few KM below the Earth's crust, when you can construct a massive, elaborate system for collecting the feeble BTUs emitted by fragile, captive human beings?


Now that is just silly. No way that would work.




maybe we should also create some sort of shared hallucination for them to continue their existences in some way 🤔


You mean like a matrix of sorts?


perhaps - it may take a few tries to perfect as well, possibly as many as half a dozen or so


What do you mean? This is a completely original idea.


no no no..I was thinking of a "grid". Or perhaps a "multidimensional array"? I got it: the TUPLE!


This is all sounding like a lot of work. Can't we just program a machine to set up this process for us?




We could feed them 3000 BTUs of food to generate 300 BTUs of heat energy....but make an awesome movie.


In the original script the human minds were used as processors, not their bodies as fuel sources, but Warner Bros thought that was too complicated.


My theory is that the battery story was just an explanation the humans came up with. The real reason is that the machines were following the zeroth law of robotics, making sure humanity as a whole would not be harmed. The humans were destroying the world, so the benevolent machines made a utopia to keep them safe in.


Certainly would've made more sense.




Yes, even at temperatures of -45C, body heat alone brings them to between -7C to 16C. https://ecommons.cornell.edu/bitstream/handle/1813/125/Igloo.pdf;jsessionid=4AC859EF61C590C9FC13DBA40B5B77CE?sequence=2


Snow in general has a good R value because of all the air trapped in it.


I live in Alaska. My buddy has a small space. He uses a hair dryer in the winter to warm up his place. So much energy is wasted with poor insulation.


That’s incredible! How cold does it get there? How big is his place?


A hair dryer can still be like 1500 watts. Just like how most space heaters you get will be 1500 watts.


Candles put out a surprising amount of energy -- about 80W worth each -- and most is heat. That's more heat than your average laptop brick. In a well-insulated environment (which an igloo is), 2-3 candles worth of power will make you surprisingly warm. Igloos are so well-insulated that they can range from around -7º to 16ºC (19º–61ºF) inside just from trapping your radiated body heat. Add 150–250W of heat from a very small fire, and you can get the space quite toasty.


It's _all_ heat if you don't let any of the light out.


A candle emits about 50W of heat. Enough to heat up a small, well insulated space noticeably.


You can try it yourself. Next time it's freezing cold outside, wrap yourself on a space blanket and light a candle inside it.


You’ll be warm for the rest of your life


> That doesn't sound like enough to warm up a person. Canadian here & we did *nature training* in elementary school. Things like what to do if you're lost in the woods. (Hint - Stay in one place, bc moving just a mile creates a search area of three square miles.) But, back to winter survival - We built tiny makeshift igloos for ourselves. Not much more than a pile of snow with a hole at the bottom but, with just a tealight & your body heat you can be comfortable enough to not wear a hat anymore. Grab some pine branches to keep yourself off the snow / block up the hole & it's even better. tl;dr You'd be surprised how quickly a small well-insulated space heats up with a small amount of heat.


You’d be surprised how quickly a candle can heat a small space, even just a single candle in a car with the windows cracked can keep you alive as long as you got wax


Yeah, actually found this out in Texas earlier this year when the freeze came through and knocked out power in my house for 3 days. I lit a candle in my bedroom (which had gotten down to the 30's) to heat it up a bit before being able to go warmly to sleep under 4 blankets and a sheet. Thanks candles!


Speaking from experience, if you properly build your snow shelter (igloo, snow cave, etc) with [a hot air trap](https://lh3.googleusercontent.com/proxy/nBoD-HzbVRWE_xvqqZ3v7rBqal2sEQqNMLsQnFuxymvgDs44_z1eJiTBwcjFRQoBrC_ledoKta3NZxEgc4zl4B-dGvzXy6vPXquQLME7Eb5_uBoNLIwcG44) Even just the body heat of a couple people can keep things warm inside. The last time I was in a snow cave it was -45 C outside, and about +16 C inside with 3 people and a few candles.


A light bulb can be enough to warm up a small room.


My computer heats up my poorly ventilated 100 square good bedroom to uncomfortable levels


My lights are LED you insensitive clod.


When I was tent camping in the snow for several months, I would burn a small lantern (little oil type) during the night. It would be below freezing outside (Mabey 5-20 degrees F). The air inside would be about freezing, or slightly above (32-40 degrees F) That is enough to keep you alive and comfortable through the night. Don't be homeless in cold climates kids.


It isn't, but it's enough to go from -10 to 50. One of those temps is survivable for long periods.


-10f to 50f is -23C to 10C for those wondering


Thanks! I was thinking -10 is survivable for long periods if you have a coat. 50 is not.


Good redditor


Point wasn't to get the inside up to the 70s, but into the 40 degree range so stuff wouldn't freeze.


back in the day my dad was stationed in alaska. he took a bet to sleep outside at 40 below. no problem. he dug a little cave in a snowdrift and it didn't take long to warm up. then he tucked into his sleeping bag, slept just fine and collected on the bet in the morning. the human body is like a radiator cranking away at nearly 100 degrees fahrenheit and it will heat up a small enclosed space quickly EDIT: removed a mistaken copy/paste that landed in the middle of my comment


You seem to have suffered a copy/paste error, reading this post gave me a lot of trouble!


I keep an emergency candle in my winter first aid kit. A little flame goes a long way when it’s balls cold


it also doesn't have to get to standard room temperature to feel warm; with warm clothes etc you can be comfortable in the 40's.


If the igloo is built properly, it actually gets pretty toasty inside just from a couple people being in there.


it isn't the only thing used. there's also just the fact that the walls are a wind break.


I have no idea how you would actually maintain a fire that small besides using.. like actual candles / lanterns.


A wick lantern with fat is traditional


They burnt seal fat/oil. Where igloos were/are traditionally built is north of the tree line. In winter seals were the main source of fresh caught food.


Yeah, the fire is just a little seal blubber. Nothing huge.


Also people really underestimate how long it takes to melt thick ice. You can have one of those huge bonfires on the surface of a frozen lake and you might melt 1 inch of the ice away.


Do you need to worry about carbon monoxide?


Not really, there is en exhaust build into the igloo and when the hot air leaves the igloo it sucks in new fresh air from the outside, making the air circulate.


And comfortable here is relative. We're not talking about a balmy room temp....




They can be in the 50s inside. Source: grew up in Alaska.


And also the snow/ice block igloos were a temporary building, think of them as a single use hunting lodge. Permanent structures were not built of the same material but of whale bone and hides etc.


> comfortable temperature It's all relative. /s


> such small room at a comfortable temperature. "Comfortable" being simply above minus 0°F and out of the wind, with the wind being the primary concern.


You don't even need a fire. The body heat of a few people alone is enough to make it comfortable.


Right , fat lamps were historically used.


Right, you are likely still going to be wearing your parka while in the igloo, if not maybe more open.


It's also important to note that the air inside needs to be vented, so it's not like the air inside keeps getting warmer with no where to go. So venting is gonna help regulate that temperature as well.


How big? And does location matter?


From what I can see, typically 70-80 degrees and a few inches across. Several sources recommend using multiple additional small holes for ventilation much further down the wall, to help CO2 and CO vent.


hot air rises to the top, so don't dig your way to China


I once saw somebody demonstrate something similar by placing a paper cup filled with water in a campfire. The fire burned only the part of the cup that was above the waterline -- but left the rest of the cup unburned -- it was a bit scorched -- but didn't burn. Its been a while since I saw this but I think eventually the water started to boil and then the cup burned as some of the water boiled off.


I did this with friends while camping once. They thought I was some kind of magician (we cooked crawdads in them). The reason here though is simple. Water boils at 212F. No matter how hot the fire is, the water will never get above 212F (pressure can change that...this assumes sea level). A hotter heat source will only make it boil away faster. Paper burns at 451F. So, the water simply never lets the paper get to the temp it needs to ignite. Voila...boil water in a paper cup nestled in the hot coals of a fire. Note: As the water boils away the top of the cup will burn away so either keep water in them or lose the cup eventually.


When I was a kid, I remember reading you could boil eggs this way


You can, I've done it.


This layer of melted and refrozen ice will then cover the gaps between snow bricks and will more effectively contain the warmth within.


It's also more reflective


Is this a good example of what Equilibrium is?


But would the people suffocate due to the co2? Just breathing would consume all the oxygen, right? Or is the small entrance enough to circulate air from the fire?


There's usually a little hole up top to allow for some flow out and the door isn't air tight so there's enough air exchange that it's safe.


What do you use for a door?


Ice block or some skins


The fire heats air which rises up the smoke hole, drawing new air in through the entrance.


You consume O2 a lot slower than you think; you can be in an enclosed space for a _long_ time before O2 shortage is an issue. The CO2 you exhale will usually be a problem first. Besides, something like an igloo is well-insulated but hardly air-tight. There is typically a "doorway" of some kind that's not exactly sealed (covered with something, but not sealed up), and a vent for the small amounts of smoke. Those two things create plenty of airflow. You need a lot less airflow than most people think, and you use O2 and produce CO2 a lot slower than most people think.


So I shouldn't immediately murder everyone if I'm trapped in a busy elevator?


Let's not get hasty


No, but establishing a pee-corner early on is crucial


[So basically. ](https://youtu.be/ZtoW4aV-CIc)


You pack the snow before cutting blocks but there is still a lot of air in the snow. It is essentially about a foot of insulation around you. The inside starts to melt and drip a little so you have to smooth it to make the drops run down the sides. The body heat of 2-3 people alone will make it warm inside. They are also surprisingly strong once the snow has set. I and another guy were able to stand on top of one with no damage to it.


A song of ice and fire then?


Brilliant, can I tack on a "How does fresh air circulate in"? Question too?


I'm pretty sure in videos I've seen they poke a hole up top to allow CO to get out and since the door isn't air tight fresh air will get pulled in.


Crackin. Cheers.


A song of ice and fire that can actually be appreciated.


I'm an Inuk from Nunavut and I have experience with this! In the colder seasons of winter often between November to April are the peak freezing temperatures, the snow packs harder from winds and cold making snow easier to pack and build into shape, forming a stronger integrity of an igloo (proper name is ᐃᒡᓗᕕᒐᖅ "Igluvigaq" ) with the cold atmosphere keeps the exterior of the Igluvigaq frozen, the interior warms by the flames of stone lamp called ᖁᓪᓕᖅ "qulliq" melts a thin wall making film of ice. The ice is kept frozen by the outside, making the Igluvigaq insulated and keeping the Igluvigaq nice and toasty! Igluvigaq are often used in temporary shelter when going out to hunt and harvest away from family camps.


Nothing to add on your comment but absolutely amazing the internet can connect people from all over the globe like to myself and yourself.




From Igloo to Loo.




If you dont mind me asking, how often would a "normal' inuk use a igluvigaq? Like, since youve said the idea is to use them as temporal shelters, id guess most people in a family wouldnt go hunting and therefore wouldnt make one that often? Also, do you usually keep to the area after constructing one? Id guess with the work it must take its not a one-night deal


>by the flames of stone lam I have witnessed an Inuk building an Igluvigaq as part of training, they are masters of the snow. Yes, 2 man can totally build a shelter in a few hours. To the untrained, it took us, 4 men, 6 to 8 hrs... for a "liveable" shelter. Our final "shape" (dome) was too high and you lose the heat rising to an unusable area, walls were also sketchy... Our teachers built the Poogloo in under 30 minutes for the demo.


Do I even want to know what a Poo-gloo is made of?


Igluvigaq 2: Electric Poogloo


Thanks. Now everybody outside the bathroom stall thinks I'm a maniac who giggles like a little girl while he poops.




Electric poogaloo haha cant stop laughing


A little gloo; mostly poo.


If I were to make a guess, it's an outhouse made of compacted snow.


it's a sticky situation


>temporal shelters Didn't realise we were discussing time travel.


Most shelters are built to withstand time travel at a rate of 1 s/s.


Wow, that's insane! Didn't realise we could build such advanced things.


Bro I dunno about you but I'm time travelling right now


This made me give and audible chuckle! Kudos to you!


Funny thing is, after writing I realized given that most structures do decay over time they kinda don't withstand 1 s/s.


Whoa I wonder how many years of trial and error did it take to perfect this craft


Someone had to come up with the idea of building a shelter with the thing they are sheltering from.


I would imagine that the first time was largely an accident. Somewhere, a natural ice wall formed and someone realized that it's not so cold inside.


Correct me if I'm wrong, but doesn't the snow also melt in a way that leaves a lattice of mostly air with some ice holding it together? The air would then soak up a lot of heat and the ice keeps its structural integrity. I don't have firsthand experience with it, but I remember all of those videos of people trying to set snowballs on fire back when it snowed in Texas. I thought that was the reason they could do that.


> a lattice of mostly air with some ice holding it together That describes the packed snow that the blocks are cut from, before any melting. "Mostly air, but the air not free to move around much" is the recipe for insulation. The ice film on the inside isn't such good insulation in its own right, but it fills up cracks between the blocks and helps lock them together quickly. > The air would then soak up a lot of heat Not exactly. Buckle in, because we're going to talk about two separate things that are closely related and easily confused: heat and temperature. Heat is energy. Temperature is the effect it has on a substance. The same amount of heat raises the temperature of a mass of metal a lot further than it raises the temperature of the same mass of water. Heat moves by radiation (infrared beams that come off of hot things), convection (flow of hot liquids and gases from one place to another, and conduction (flow of heat between things that are touching). In a snow block, all that ice baffles the flow of air, and its reflectiveness quashes radiation, so conduction is all we're left with. And conduction has the fun property that its efficiency depends on a temperature gradient. Try and conduct heat through ice, you will find that you can't get much of a temperature gradient in it. Ice has a massive heat capacity (ability to absorb heat energy without its temperature changing much), and it has a massive heat of fusion (amount of heat energy necessary to melt it, during which process its temperature doesn't change at all), and then when it's melted, the liquid water still has a massive heat capacity. This is all thanks to what water is made of: densely packed molecules that have lots of ways to stick to each other. The temperature depends on how fast they move, and all that stickiness means that when you try to make some of them move a lot faster, instead you make them and all their neighbors and neighbors' neighbors move a tiny bit faster. Upshot: All the heat you dump into the innermost surface of the igloo raises its temperature only a tiny bit above the ice just outward of it. Tiny temperature difference means it doesn't pass heat outward very fast. Now, what about the air? Per mass, air has a hundred times less heat capacity than water. But the mass of air trapped inside those snow blocks is tiny. Both of these are because air is a tiny pinch of detached specks of matter banging around very fast in a huge amount of nothing. So yeah, a bit of heat coming into an air molecule can make it zoom, but the molecule is tiny, so the actual amount of energy it transfers into whatever it hits is also tiny. If you want to move heat with air, you have to let it flow, which the packed snow and the ice shell both obstruct.


Did you just well actually an Inuk regarding igloos based on videos you watched? 😂


I want to share a joke my 7 year old son made. Why couldn't the boy from Iqaluit watch the baseball game, he couldn't see Nunavut (none of it). Lame but funny too. Thanks for the explanation including proper names!


Not gonna lie, that written language looks like what a biblically accurate angel would speak


Wow, that's so crazy. Thanks for sharing, I guess I've always wondered how this works too. Your people are mad smart to build shelter out of snow and survive lol


An important note is that the goal of warming the inside of the igloo is NOT to keep the inside a temperature that you would be comfortable in your home. It is to make it more comfortable in clothes and blankets. The structure does melt if the internal temperatures get too high. As others have said, you want to find an equilibrium so that the melting is not happening faster than refreezing. If you want the structure to last more than a few days, the internal temperature needs to be fairly low, say 40s or perhaps up to 50s. This is a welcomed respite from negative temperatures in the arctic. Snow melt, humidity from your body, and breath will freeze into the cracks, helping to seal the structure and block wind and the elements from infiltrating. However, ice is a much worse insulator than the packed snow initially used to create the igloo, so you don't want the walls to too thick with ice. The ice also helps trap moisture inside, thus increasing the relative humidity inside of the igloo. Super cold air is very dry, and can make it painful to even breathe. Humid air also holds heat better than dry, so a small heat source can provide a better warming effect when the humidity is slightly higher.


Snow with an ice layer over it is very insulative. That keeps the heat inside and the cold out. It also keeps the heat out of the actual snow and the ice sort of keeps itself cool. It is the same reason that snow that has a crust of ice takes so long to melt even if it is way above freezing.


As someone who has built and slept in an igloo I'll say they get very warm inside. It got to the point where I couldn't stand being in my sleeping bag anymore and had to unzip it. The inside will start to melt a little so you have to make sure it is smooth so the drops run down the sides inside of dripping. Getting in and out of an igloo though is like crawling in a sink trap so you have to put all your clothes back on to slither in and out.


What’s a sink trap?


The curved pipe under your sink that prevents odors from coming back out. In an igloo you don't make an entrance straight into it, you make one that goes down, under the wall, then back up. That way you trap the warm air inside.


So it's not the "cartoony" igloo with a dome and a low curved door, but rather a dome with an underground tunnel?


That is exactly what I point out. You don't have to make a nice entrance but it helps. It is also a spiral instead of a series of layers. You put one row of blocks down, cut them to make a slope that leans in a little, then add your blocks from there. It will make a spiral up to the top. One person stands inside (you build it around them) and helps place the cap block on top. Then you dig the entrance tunnel down and up into it. Finally you pack snow and chunks into all the gaps you see and smooth the inside. You can make a nice little enclosure around the entrance like in cartoons though to give some more protection from the elements or just stuff your packs over the entrance.


I decided to look it up after this thread and saw this [https://i0.wp.com/moss-design.com/wp-content/uploads/2014/12/igloo.jpg?w=877](https://i0.wp.com/moss-design.com/wp-content/uploads/2014/12/igloo.jpg?w=877) really interesting.


That’s the most boring porn I’ve ever seen


Idk why this made me laugh so hard


Oh god I’m way too claustrophobic for that


It's actually a pretty gentle curve, just enough that warm air can't easily escape. You can also put your packs over the entrance to block the wind.


It's the "U" or "S" (if the S was on its side) shaped pipe at the bottom of the drain. This keeps a low area filled with water even if you don't run the sink in a long time, which acts as a seal against sewer gas coming back up through the plumbing system.


I learned how hard it is to melt snow/ice with fire in an interesting way. My boss told me to we had a “parade” of higher ups coming through. There was a bunch of dirty snow in the parking lot. I went to Home Depot and rented the biggest kerosene heater I could. Had guys pack it up high and pointed it right at the base. Maybe an hour later very little progress. One of the guys who reported up through me walked by, called me a dumb fuck and said that’s going to take forever. It was 60 degrees out and he grabbed 2 guys and they broke it up and threw it in a thin layer over the parking lot. Took like 2 hours to melt on its own after that. It would have taken us a day to melt it all. Anyway, getting schooled by a technician was fun. Little did he know I just wanted to play with a kerosene heater. But, he did get to call me dumb which was a positive for him and taught me a lesson on how many BTU’s it takes to phase change ice to water.


Heat of fusion does hit that way. It's part of why phase change cooling is so effective. You can sink a ton of heat into the phase change (called heat of vaporization when going from liquid to gas or back). In case anyone misunderstands, there's an extra "jolt" or "step" of energy required to get ice at ~0°C to water at ~0°C and vice versa beyond just "heating it up" which is called "heat of fusion".


Also the reason why fridges, deepfreezer and air conditioner are one of the most effficient devices humans ever invented. The phase change of the refridgerant carries so much heat energy with so little work that some devices achieve above 95% energy efficiency.


especially those top door brick-shaped freezers. They are impressive at keeping stuff cool at minimal energy consumption, especially when they are packed full.


If you want some of the math behind this: [https://what-if.xkcd.com/130/](https://what-if.xkcd.com/130/)


It is a lot harder to melt ice than most people realize. It's not just heating ice from 0C to 1C; you have to add enough heat to cause a state change, which doesn't even change the temperature. You are basically melting 0C ice into 0C water. Which also means that the melted ice doesn't help you melt more ice. [Here is a documentary that explains it better than I could.](https://www.youtube.com/watch?v=uKBtFUufqL0)


https://howeverythingworks.org/1997/01/10/question-730/#:~:text=But%20while%20a%20central%20fire,and%20it%20won't%20melt. To avoid melting the ice, people must keep the ice below its melting temperature. That means that they can’t add heat to ice indefinitely. But while a central fire will always deliver some heat to the ice of the igloo, the ice of the igloo will also tend to lose heat to colder air outside. As long as the ice loses heat at least as fast as the fire delivers heat to it, the ice won’t become any warmer and it won’t melt. Water has a lot of latent heat. This means that it requires a lot of energy to transform water from ice to liquid, even though the temperature stays at 0°C. Furthermore, water has a high specific heat capacity, which means it takes a lot of energy to change the temperature at all. And finally, even though the air inside is maybe ~10°C, the outside might be waaay below 0°C, and might might be windy, causing the equilibrium temperature of the ice to be well below 0.


Conduction vs convection. The convective heat put off by the fire just isn’t enough to overcome the amount of heat that the thick walls of an igloo can absorb through conduction. It would take an immense amount of BTUs to melt the walls of an igloo. Ever seen the video of the guy trying to melt the snow on his driveway with a flamethrower? It didn’t work very well…. It takes only a small amount of convective heat and few BTUs to warm the air inside the igloo. Think about breathing on the palm of your hand. The surface of your hand gets warm for about 3 seconds. But you could never breathe on the palm of your hand enough to make the back of your hand warm. Now imaging the back of your hand is -10 degrees. Your hand is going to be frozen regardless of a little warm air hitting one side of it.


It looks like your question was mostly answered. I would add that another good example is that ice fisherman who are out on the ice for the day (not in a fishing shanty) sometimes start a fire on the ice for warming up and cooking. The ice melts a little and then a layer of cold water battles with the fire on one side and the ice on the other (very similar to the layer inside the igloo). Even after a full day of fire, it will only melt a few inches into the ice.


I have a follow up question about this: How come mountaineers never seem to build igloos (ᐃᒡᓗᕕᒐᖅ as /u/IpodAndMp3 stated) when they get in trouble on a mountain? For instance, in the 1996 Everest disaster, where 12 people died, not one had tried to shelter in the snow (as far as I know). In addition to that, I have never hear of *any* mountaineer trying to shelter in an igloo to combat exposure - which seems obvious for a number of reasons: snow is abundant and a professional camp stove is very light, compact, and can be used to make water from ice - I would assume that would be an essential thing on the way to the summit. Now, I realize the Everest disaster has many, many, other factors: HACE, massive storm / wind, well above the death zone, lack of O2, fatigue (especially), etc. I am not trying to suggest I know shit about anything in this regard - it's the one example I can think of. I am legit curious and as, like I said, I haven't heard of this type of shelter in any / many exposure incidents. My best guess is that snow on the tips of mountains are not "sticky" enough for this sort of endeavor? Anyways, enlighten me.


Igloos often have a small hole in the side and one on top. The side hole allows fresh air while the top hole allows CO and smoke to leave. Much of the heat also leaves through that hole.


They say if you ever get stuck in a car in the middle of winter, a tealight candle on the dashboard can provide enough heat to get you through the night.


Not an igloo expert, but am firefighter trainee. Fire science is... wild. The stuff you learn in high school chemistry doesn’t hold a candle(eyyy) to the real thing. Heat wants to rise and so does fire. You know how they always say close doors and windows to contain a structure fire, and how modern buildings have actual fire doors? Basically what this does is contain a fire until help arrives. It’s not going to put it out. What firefighters do in a fully involved fire is the exact opposite. They vent the roof directly above the hottest part of the blaze. This causes both smoke and heat to escape vertically so that a fire attack team can enter from the side and extinguish the fire without being melted. Turnout gear and water vapor alone have their limits. In addition, water doesn’t magically extinguish fire, as you can see from oil fires burning on water. Water only cools the fire’s fuel below its ignition point and thus puts it out. So I’d imagine with the igloo scenario, enough heat escapes vertically that the interior is warmed without melting the ice, and the cooling effect of the outside air on the ice keeps it in a solid state. I’m sure many igloos have melted from too much fire and too small a chimney.


I also always wondered how they are ventilated?