58

Is it warmer to sleep in a car or in a tent?

Suppose that our old internal-combustion-engine car breaks down in a remote place at -30°C, -40°C, or -50°C, and the engine won't run at all. Suppose we're travelling with a single car, but we did bring full camping gear, including winter sleeping bags and a good double walled dome tent that we can squeeze into together with all passengers. We also have some candles to make heat. It's getting dark and we will spend the night hoping for a passer-by tomorrow.

Faced with the choice is sleeping in our broken-down Toyota or in a tent, what would be warmer? We may be able to bury the tent partly below the snow. Assume no wind.

See also: My car broke down in Siberia. What do I do now?

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    I guess we're assuming that you would use your sleeping bags if inside the car, right? (ie: the only variable being tent vs car; all other things equal) – Roflo Mar 21 '18 at 20:00
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    Four people in a Toyota aren't going to get any sleep. Yep, you're all going to spend the night hoping for a passer-by, until you draw straws for who's going to go make a fire - and then all of a sudden you're camping. Isn't that what you came (and were prepared) for? --- A tent, because it's in contact with the ground. Assuming there's no wind is a bad idea, because there will be, and that's why you don't want to be a foot off the ground. – Mazura Mar 22 '18 at 0:24
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    The premise of this question is slightly off. You're much more likely to be broken down in a GM or a Ford then a Toyota. – Mark Mar 22 '18 at 18:12
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    @Mark Maybe I would refuse to set off in such conditions in a GM or Ford in the first place ;-) – gerrit Mar 23 '18 at 11:22
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    *** Picturing that gerrit is stuck on a desolate road in Siberia, only can get data from his cellphone, and rather than alert anyone, has opted to post here and has been desperately checking and rechecking for answers *** – JeopardyTempest Mar 26 '18 at 4:25

12 Answers 12

47

I suggest using both the car and the tent together.

A car will lose heat fastest through the windows, so use the tent to cover them (and the top). The windows are a thin single layer of glass, while the panels trap a layer of air between the metal outer and a lining that is a better insulator than glass. The panels also block radiative heat loss from the interior. Lower panels tend to have noise absorbing pads covering some of their area, and these have some insulation value. Even a tent big enough for 2 should cover the windscreen and front windows with a couple of layers of fabric and you can get in through the back doors; a 3-person dome would go right over the top of a small car.

This approach has another advantage: it will attract attention. A car could pass before you can react if you're huddled inside a tent to keep warm, but in difficult conditions a driver would be likely to stop for something so out of the ordinary

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    Once I slept in a car with my brother when outside it was about -10°C, little less. We covered the windscreen with a blanket, turned on the heater and the seat heaters for 10 minutes before going to sleep inside our sleeping bags and did quite fine. Twice. – clabacchio Mar 22 '18 at 7:51
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    Ah, until I got to the end of the first paragraph I thought you were suggesting trying to set up the tent inside the car. – DasBeasto Mar 22 '18 at 19:52
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    I thought it was a 10 man tent and you were going to push it inside ;) – Mazura Mar 22 '18 at 23:47
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    If you have one manner or a small 2 manner it would fit in the back of a big estate and or a big 4x4 with the seats down. This would almost certainly be the warmest scenario. You could easily pitch the tent in there, using the front seats, foldy-handles and boot pistons to tie onto :) – josh Mar 23 '18 at 15:09
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    @Quaternion I see where you're coming from. But I think I read the premise of the question slightly differently. If the gear was meant for these conditions there wouldn't be a question - or not this one; the answer would surely be to camp right next to the vehicle. It seems more like they've got caught out by much more severe weather than expected, or broken down crossing a pass while equipped to camp in a sheltered valley. My conclusion would also apply if they were carrying a large group shelter rather than a tent, which is perhaps more likely – Chris H Mar 24 '18 at 7:23
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The car, mostly because you can use the heater. You will want to make sure that the exhaust is clear to avoid carbon monoxide poisoning and only run it for a short periods at a time. This also helps keep the engine warm, as it is much harder to start an engine when it is really cold out.

If the the engine quit working, like say you hit the oil pan and froze up, you will still want to stay inside, since the car is already warm as opposed to setting up the tent and then having to try and warm it up with body heat and candles.

Also, the car will be dry inside, while the outside may have snow and ice since its winter.

Going outside to set up the tent will expose you to more cold than simply remaining in the vehicle.

Your vehicle will also be more visible and most people would assume that is where you are. If you were camping in the woods, they might assume that you had hitchhiked out of the situation.

One last note, from personally having slept in vehicles below freezing before, be prepared to scrape frost off both the outside and inside of the windows.

If you’re stuck in your car and immobile, first, call for help. Don’t overexert yourself and don’t leave your car and begin walking for help. Typically, you have a better chance of being found if you remain with your car, which may also provide the best shelter from the elements.

...

Instead, be sure the exhaust pipe is free from snow and roll down a window enough to vent the car and prevent carbon monoxide buildup. Run the car for short 15-20 minute intervals to warm up and then turn it back off, using blankets, a sleeping bag, hand warmers and the body heat of others in your car to stay warm.

Source

If your car starts and has fuel, use it for heat. Cover the bonnet so that as little heat as possible is wasted - but always make sure that the exhaust is clear. Note: Do not go to sleep with the engine running.

Source

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    I don't get it. Shouldn't a snowcave outperform both by a lot? – Joshua Mar 21 '18 at 22:36
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    @Joshua You would get pretty wet during the construction and it would take a while – Reinstate Monica Mar 21 '18 at 22:38
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    Turning off the car is important - if you fall asleep and the exhaust gets covered up by snow (or something else, or something in the car breaks), you could die of carbon monoxide poisoning. That's exactly how my aunt died. – BlueRaja - Danny Pflughoeft Mar 22 '18 at 0:16
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    @Joshua a snow cave requires specific tools and skills and a certain snow conditions. Unless your already familiar with snow caves then thats not a likely option. This question is more common when people travel to unknown places or underestimate weather. – FreeSoftwareServers Mar 22 '18 at 9:33
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    Making a snow cave requires suitable snow, the right equipment (shovel or saw), a few hours, a change of clothes and a lot of energy. It is an appealing idea, but not as straightforward as people imagine. – copper.hat Mar 23 '18 at 16:53
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I can't say with certainty about which would be better, but I can speak for the survivability of spending a night in a tent at nearly -30°C(acutally -20°F/-28°C). As a boy scout, my troop and I once shared a large canvas tent while winter camping in Idaho and we were all blissfully unaware of how cold it actually was outside.

In the morning, our leaders told us that the outside temperature was -20°F, which they measured late at night by checking the thermometer in one their trucks. There were probably 4 boys in the tent. The leaders slept in a separate tent. I slept in a zero degree synthetic mummy bag and though I remember being a little chilly, it wasn't the worst camping experience I have ever had. I have also spent a few nights in car and have often found that not very comfortable temperature wise or otherwise, but I can't remember if I had my zero degree bag on those occasions.

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    Each human is a heat source. The exact same tent with fewer people in it would be colder. – Harper - Reinstate Monica Mar 22 '18 at 15:19
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I have slept many nights in a homemade conversion van From experience getting up at dawn, it usually feels warmer outside the van then in it.

There are probably scientific words for it; but the metal gets cold and "sucks" the heat away from your body.

If you have a tent, AND IF IT IS SAFE to set it up where you are, and if you have a good insulator between you and the ground. I would pick the tent if warmth was the only concern. Additionally it will be easier to get comfortably stretched out in the tent.

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    It's "thermal mass". The air changes temperature rapidly, the metal of the car is much slower, slowed further by its insulation, so you're still "enjoying" the cold of night. (and to be technical, "mass" isn't quite right - mass doesn't store heat, atoms do since heat is the energy state of an atom. The best thermal mass is not lead, but water because water packs a lot of atoms in a small space.) – Harper - Reinstate Monica Mar 22 '18 at 15:27
  • @Harper, Well... atoms also store mass, but yeah, it is a separate thing. – jpaugh Mar 26 '18 at 15:04
8

It depends.

Your question says that you have a good set of camping gear. A properly set up tent, with the right gear can be quite warm. Much better then a car. A car will loose heat quite quickly. Running it, specially in the snow, can be deadly.

A proper set of gear will keep you not only warm but comfortable.

There is a vast difference between a thin walled pop-tent, that is designed to be used in the spring and summer, and a proper setup (including a ground mats, bags and barriers). If all you have is the wrong kind of tent, your car may do better.

Now that said, if your talking about an emergency situation, where you don't have a proper set of gear, then a tent could really suck.

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    Right. The question did specify "a good double walled dome tent". – gerrit Mar 23 '18 at 14:26
  • That's what I meant, I will clarify. – coteyr Mar 23 '18 at 14:42
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    Aren’t even winter tents still quite well ventilated to prevent condensation and ice on the walls? I have no experience with real winter tents but 3-season tents only help to keep the wind and rain/snow out. It will be barely warmer inside (maybe a °C or two). The only significant insulation is provided by the mat and sleeping bag/blanket. – Michael Mar 24 '18 at 11:45
  • real winter tents even "good" three season tents should be much warmer then the outside. We have a three season tent that has "three" configs. In the first it's basically just mosquito netting. The second is good down to about 0 degrees C. The third config has an "air lock" so that when you have to go out you don't let out the warm air. It has a separate "'dressing" area for putting on boots and what not. I don't even want to know what that will work down to. Probably the -20s. I have seen many cold weather tents rated down to the -50s. – coteyr Mar 24 '18 at 11:58
  • @coteyr "... is good down to about 0 degrees C. [...] rated down to the -50s." And what exactly does that even mean? I can (and have) taken my 0 degree sleeping bag out into 0 degrees and used it outside (ie: something overhead and blocking direct wind, but still getting wind and snow on my bag) and been just fine with no tent. I doubt I could sleep on the floor of a 0 degree tent with no bag in 0 degrees and say the same. So what does that even mean? That the tent can physically withstand the temp without freezing/breaking? If that's all it means, that's good but doesn't really support you. – Loduwijk May 22 '18 at 23:08
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You should stay in the car, just sleeping on the ground will suck a ton of body heat. Even if you do have a cot, most tents won't keep heat nearly as well as a car, since most car's do have some amount of insulation.

To make sleeping in the car a bit more palatable, you can cover the car with loose snow if available (use a floor mat as a scoop); snow is actually a decent insulator. Make sure you remove the snow from around the exhaust so you can periodically run the car's heat without succumbing to carbon monoxide (Just run it till you get warm and turn it off to preserve fuel)

You'd be better off using the tent fabric as a blanket(s) and using the tent poles to hang a message on in case you get snowed in.

On a side note, its always good to keep a gallon of distilled water in the car for emergency situations. Not only can you drink it in an emergency, but it can be used to temporarily fill your radiator to get you to a safer location. (In a real emergency you can go all "Red Dawn" and use your urine)

You can make a small heater using an empty metal container (soda can), a piece of paper (for a wick) and a fuel source (such as alcohol, a spare quart of motor oil or even hand sanitizer).

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    In the question, I was assuming that the car has died, and thus that running the engine would not be possible. – gerrit Mar 22 '18 at 19:04
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    @gerrit Even if the car is disabled, the engine could still run. For instance a broken axle, blown transmission, or even having more flats than spares... You know what they say about assumptions. Either way, I did mention an alternative source of heat in case it won't run. – technosaurus Mar 23 '18 at 2:20
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    "sleeping on the ground will suck a ton of body heat" If you have winter sleeping bags you should also have closed pore foam pads or the inflatable ones. Add any extra clothing, fabric car floor mats or trunk liners. In extreme, slash off car upholstery. Also, many sleeping bags are designed to zip together in pairs "for added warmth". – Keith McClary Mar 23 '18 at 4:39
  • "snow is actually a decent insulator" Yes, but it's also cold. Whether this is a good idea depends on the temperature of the snow and the surrounding air (and the amount of wind). – Acccumulation Mar 23 '18 at 19:11
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    @Quaternion Unless OP updates the question with something less vague than "full gear" including its condition and their familiarity with the gear its pure speculation. If some city boy has the best gear in the world that fits in a toyota, but uses up all his body heat trying to set it up, its useless. – technosaurus Mar 24 '18 at 16:19
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The question supposes that you have winter camping gear. It would be warmer and more comfortable to setup in the tent. You have already specified that the tent could be partially buried (most winter tents I'm familiar with, this is part of the normal setup in any-case). You can't set you your equipment out properly in a car, and it is not designed for winter camping.

This of course supposes that you really do have effective winter kit. I have been on roughly a dozen winter camping trips, which have reached temperatures lower than -30 deg C (I think the record was -42 deg C). We slept in tents for all these exercises, and were outdoors for three nights, each time, there was nothing but our kit to keep us warm.

Here is what we did, some of this advice is dangerous and for recreational camping would suggest simply not camping at such low temperatures, but the Canadian Army (well the Infantry, this isn't a requirement for the rest) seems to think its troops should be effective at all temperatures:

  • Use the best sleeping bag available, for us that meant two -20 deg down filled sleeping bags (while some might not think that makes sense, it is very versatile)
  • If possible invest in a Gore-Tex sleeping bag cover; this is quite expensive, but with a bit of tarp you can literally embed yourself in a snowbank and sleep.
  • Use an air mattress, the best ones in my experience are not pretty, they look like they are made out of what looks like bicycle inner-tube, and provide about 6-12" of lift, this provides very good insulation against the ground. Also ensure you use the air-scoop (a feature some air mattresses have), or a hand pump, you can't mouth-inflate an air mattress in the dead of winter if you want it to roll up in the morning, and/or not be full of ice after a few uses.
  • I don't have much opinion on the tent, should be a winter tent, the ones we used were highly flammable. Tents capacity are generally assumed to be shoulder-to-shoulder, in the winter a full tent is very helpful.
  • Heating [this is where things get dicey]: - Candles are quite risky in my opinion, a Coleman lantern is much better, it throws reasonable heat and provides excellent light, you can carry it around outdoors. It is a good investment in the event of a power failure. A second method of heat; which is quite dangerous, is the use of a Coleman stove, which we would actually light indoors! (although by protocol you are definitely not supposed to!). If you are not able to stand comfortably in the tent, and you are not really proficient in the use of your stove such that you can get a flare up under control, then light the stove outside (or you won't have a tent). The stove can not be left on unattended, so it is just used to heat the tent initially. The lantern can be left on all night but should be turned down. This will produce carbon dioxide and monoxide, not enough be life threatening, but enough that you may feel a bit hungover first thing in the morning. Also be aware that under very low temperature conditions, filling the stove and lantern is a frost bite risk, so be careful not to get the fuel on you.
  • try not to wear much clothing when you sleep, you want to have enough clothing to be comfortable but you don't want to risk sweating; at some point you'll get to get out of your tent and what once was effective winter clothing will now be compromised.
  • A final note; it is best to camp when the temperature is very stable, beneath freezing, -20 deg C is safer than 0 deg C. More deaths happen where the temperature fluctuates around the freezing mark. This is because people underestimate the severity of the temperature, and they will get rained on and then then the temperature will drop beneath freezing. If the temperature is close to the freezing mark, it may be better to stay in your car unless you have rain kit in addition to your winter kit, even so it is a PITA.

Since you have a break down of temperatures, my only advice at -50 deg... you will die without a proper setup, if your car is dead... get out and set up quickly (again, assuming you have the kit). Otherwise there is plenty of advice already here in the other answers regarding what you could do to survive longer in your car.

  • What is an "air scoop"? I just googled "what is an air scoop on an air mattress" and found no relevant hits, the hits involving air scoops being for cars and not mattresses. Kudos on your great experience! I don't understand the aversion that even other outdoorsmen have to winter camping. The coldest I've slept outdoors was about -10 or -20 C, though I was perfectly comfortable and slept in only my boxers otherwise I was too hot. Again, I'm not familiar with this air scoop; could you point us to more information? – Loduwijk May 22 '18 at 23:33
  • Sure, they probably go by different names and come in a couple different styles. A common style is a rubber connector which is found the side of the bag which holds the air mattress, you can fit this connector over the connector on the mattress, you then scoop up some air, quickly close the open end (where you would have taken the mattress out) and tightly roll the bag towards the mattress forcing the air in. The mattress has a valve to prevent the air from escaping. Repeat until full. Another style is similar but the scoop is attached to either the head or foot of the mattress. – Quaternion May 22 '18 at 23:44
  • The ones that come attached to the mattress are about the size of a pillow case and are much more efficient than the little bag an air mattress typically comes in. – Quaternion May 22 '18 at 23:47
5

Unless you can still use the car's heating (which usually presumes the motor still works). You're definitively doing better inside the tent.

This can be told both from experience, and science-based.

I've once slept in a car at slightly-below-zero before. Half an hour and you're done. On the other hand, sleeping an entire night at sub-zero in a tent curled around a young woman is not only tolerable, but quite comfortable.

As far as science goes, a tent will have a heat transfer coefficient of about 4-5 for each layer of fabric (so somewhat below 4 if you count them both), but the layer of resting air between the two walls significantly reduces the overall figure, to about one half. Heat lost is due to radiation, convection is (practically) zero, assuming you're not sleeping on the naked ground.

The car's windows will have a heat transfer coefficient anywhere from 6 to 8, and the chassis, although somewhat insulated, will not be much better since the metal is an excellent thermal bridge (with transmission coefficients in the 50-60 range). You have two sources of heat loss here, radiation and convection. Metal is awesome for convection. Not so awesome if you want to preverse heat, though.

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    The young woman seems somewhat of a not very relevant detail? Body heat does not depend on age of gender (but a partner with a lot of body fat may be advantageous). And do you mean 0°C or 0°F? And what are the units for your heat transfer coefficients? – gerrit Mar 23 '18 at 11:20
  • @gerrit: My personal experience with tent-sleeping sub-zero is limited to sportive ~22yo females. Those demonstrably radiate a very comfortable amount of heat (though others probably do as well). Obesity may be a disadvantage as fat is inert (white fat in the adult at least) and a strong insulator. Unit is Watts per Kelvin square meter. Thus, per unit, if you have, say, 12 m^2 of tent surface and -20 outside, and you want to keep up +10, you lose 360W to the environment. So whether that's multiplied by 2, or 6, or 8 is a huge difference. – Damon Mar 23 '18 at 13:11
  • "lose 360W to environment" is probably a bad wording, but you get the idea. You could as well say you need to burn 360J (86cal) per second to keep up the temperature. With that in mind, something as high as +10 is virtually impossible to keep up, as you can figure (I just assumed some random number, the math works either way). Assuming you sleep 8 hours, delivering 360W would be an extra 2.400 kilocalories that have to come from somewhere... – Damon Mar 23 '18 at 13:18
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    It never struck me that obesity is actually selfish ;-) – gerrit Mar 23 '18 at 14:27
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    I believe you mean "conduction," not "convection." Most metals do conduct heat very well, though I'm not sure a lot would be conducted from inside the cabin, through relatively narrow metal axles and suspension, through rubber tires, to the cold ground. – Jon of All Trades Mar 26 '18 at 14:21
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Neither. You need to change your perspective. Both the car and tent will "leak" heat, as neither one has very good insulation, even if you are using a 4-season tent. Think of both as a form of shelter. Your shelter protects you from the elements such as wind and rain; it keeps you dry. Your sleeping bag or blankets or layers of clothing is what will keep you warm. When planning a sleeping bag purchase, remember that the temperature rating on the sleeping bag indicates the temperature at which you will survive in the bag; for a comfort rating assume 10 to 20 degrees warmer.

In the winter, wind and water are your two enemies. If getting out of your car to set up your tent means you will get wet, stay in your car. If you can safely set up your tent and stay dry, then set up your tent so you can stretch out comfortably in your sleeping bag.

3

Unless the car can provide heat (either engine or independent heater), tent is a better choice - car is not designed to keep the heat inside; tent is.

Car is mostly metal and glass, both poor insulation materials. They will get cold in no time and then will cool down the air inside. Note that the car's windows are single-pane. Windows in buildings are not comparable, as they have air between the panes.

While the tent's two layers of fabric may seem like not much heat protection, it's the air between them that's providing the insulation.


I have slept in tent on snow and it was fine. I also slept in a car in about 5°C (in a sleeping bag) and was woken up by the cold in very early morning and had to start the engine. A relative of mine often went skiing and slept in a tent pitched right in front of their car (they now have a car with a heater and sleep in the car since then).

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    The important part here is the double wall construction of the tent - there are single wall tent's which do not benefit from this insulation. – imsodin Mar 23 '18 at 9:52
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I've done enough crazy camping in the UK to know how best to get chilled to the bone in a mild climate. Assuming you do not have sleeping bags and you have a single-skinned tent then the car is best because you can run the engine every time you wake up frozen, unless of course you're in this pickle because you ran out :) I will not run the engine while I'm asleep in the car and anyone who does this in drifting snow is dicing with death. In the tent you can spoon with your buddy and/or your dog but a one-skin tent always sucks beyond belief. If it rains then you just have to get back in the car!

A two skinned tent is routinely better than a car if you can pack enough heather or, better, a plant called Bedstraw under your points of contact with the ground - the major way you lose heat.

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    Anyone managing to get cold camping in the UK has only insufficient equipment to blame. You may note that even the highest temperature noted in my question is lower than the lowest temperature ever recorded in the UK. But your point about Bedstraw is interesting, could you expand on that? – gerrit Mar 25 '18 at 20:42
  • In my case I think it's insufficient brain that's to blame, and insufficient dosh. But bedstraw is everywhere and really works, and I now see that you can eat it too: en.wikipedia.org/wiki/Galium_aparine – Aethelbald Mar 26 '18 at 17:57
  • @gerrit I have not been camping in the UK but I'm very familiar with the area around Ottawa (as far as capital cities goes, gets more freezing rain than any other). The UK is famous for it's "wet-cold" which people often talk about in Ottawa too. Where I am now: Edmonton, AB, CA, we are typically quite arid, temperatures can drop much lower but it is more comfortable here because of the low humidity. Fun fact: You can get fog even in the winter... some don't know but water in fog can go beneath 0 deg C, lots of the UK has miserable cold fog. I honestly would rather be at -20 than -5 to 5. – Quaternion Mar 28 '18 at 21:42
  • Here (Edmonton) we sometimes get ice fog (different from freezing fog) at about -40 deg C and it produces a really cool effect called "light pillars". Apparently in Siberia the ice fog can get so thick and still that children can play a game where they guess who traveled though the fog as it holds it shape, and they can follow the trails to the other child to see if they guessed correctly. Freezing fog can even sink ships. I'm just pointing out ways water can be interesting and be a terrible nuisance even at these relatively warmer temperatures, hypothermia does not take much. – Quaternion Mar 28 '18 at 21:53
3

The answer is it depends.

Sleeping bag and insulated pads is the same.

Vehicle

  • Wind proof and water proof. But it is not going to be raining at -30°C.
  • Glass and metal are not good insulators. Glass is less insulation. Glass suffers from radiant heat loss.
  • More surface area for more heat loss.
  • Up off the ground so you are insulated from the ground.

Tent

  • A good winter tent is water proof. Not totally wind proof.

  • Typically less volume compared to a vehicle so you can better share each others heat.

  • Not a great insulator but a double wall tent is certainly better than glass.

  • More comfortable to sleep in a tent.

  • You can pitch the tent in a chosen spot.

Situation I think situation will dictate.

  • If the car is on a ridge without protection that would favor the tent.
  • If there is good natural shelter near by that would favor the tent. Tree canopy and hill to block wind.
  • High wind will favor the car unless there is natural shelter you can get to with the tent.
  • Snowing it would favor the car as you don't want to get wet.

  • Getting dark favors the car. It takes time to pitch a tent.

  • Rescue probably favors the car if the tent is not visible from the road.

If you go with the car. Push it to better shelter if that is an option. I would use the pads on the windows (inside or out or both) if you can hold them in place. Then cover the roof and windows with the tent.

Again it depends. If you have proper sleeping bags you are going to do OK. A nice tent like a climbing tent then I think I would go with the tent in most situations.

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