Table of Contents
how to sleep comfortably and healthier at 7deg C without a sleeping bag
see also:
Waking up in morning fog 2degC but inside the 2P tent, a lovely 14degC - Kurth Kiln 2022
This is one reason why I like to have my tent open - just need to open my eyes and see the beauty and smell the fresh morning air and fall back asleep to dream of what the world could be while making the most of the present - just bliss!
Often I put an eye mask on to block lights and noise cancelling headphones on to block noise so I can concentrate on the gentle cool breeze on my skin, the lovely sensations of the warmth from the electric blanket and the scents of nature (although sometimes the scent of a wombat needs to be addressed and the wombat shown the door from the 4P tent - don't shine your bright torch it will just panic and tear your tent!)
Life is too short not to live it
Introduction
- The aim of this is primarily to warm up the air you breathe so you don't get bronchospasm, coughing, runny nose, dry throat and poor sleep.
- NO ONE gets healthier or enjoys sleeping in cold air!
- The warm air eradicates tent condensation even in thick fog so you don't end up cold and wet
- you will NOT be able to heat a larger space such as a 4 person tent or larger in this manner - it is possible 2 naked campers and 2 electric blankets could heat a 3 person tent but I have not tried this
The Secret to maintaining warm air to breathe
- ensuring your air space to warm up is as small as possible (hence a 1P or 2P tent) with as little air exchange as possible with the outside air (hence ability to fully close it as needed - ie. all fabric inner rather than mesh)
- using your body to heat the air (100W) instead of your body heat being confined inside a sleeping bag
- using a 25-50W electric blanket or heating mat to keep your body warm enough so you don't shiver and at the same time contribute to heating the air
- using a quilt or open sleeping bag to cover your body as needed - especially your lower legs and feet which tend to get cold.
- a great quilt style for hikers are quilts with sewn-closed foot boxes such as https://enlightenedequipment.com/enigma-custom-sleeping-quilt/?avad=351957_f3b00a049
- the average 2P tent has an interior volume of around 2700L (2.7m3)
- human body at rest generates around 90-100W of heat
- a relatively sealed full fabric tent will thus be heated by the human body and temperatures will generally be significantly warmer than outside
- an additional factor will be the expired air temperature which is usually 31.4-35.4 °C at 4.5L per minute - if tent temp was 10degC, after 30 minutes of breathing the expired air of 135L at 35degC would theoretically raise the mixed tent air temp by about 1.5degC - the main downside is the humid air will form condensation on the inside of the tent if there is inadequate ventilation so you will need to balance this or have a towel to wipe it off.
- a healthy person will not die from lack of oxygen or excessive carbon dioxide due to a enclosed tent even if you had a fully sealed 2P tent for 1 person overnight
- assumption that air is continually mixed inside tent (hot exhaled high CO2 air rises to top then cools and heavier CO2 sinks creating a continual circulation aided by movements of the body while sleeping
- volume of 2 man tent = 1.3 x 2.1 x 1m h = 2.73 cu m = 2730L
- minute volume of breathing = 5L/min
- CO2 concentration of exhaled air = 5% or 50,000 ppm
- thus each minute, the tent CO2 levels will increase by 50000 / (2730L x 5L) = 3.66ppm
- thus time to reach 5000ppm or 0.5% (the max. industrial safe level for prolonged breathing) = 5000/(3.66 x 60min) = 23hrs
- thus in theory, over 12hrs overnight in winter, the CO2 should only rise to 0.25% or 2500ppm which will not be problematic for healthy people (it may be problematic for those with COPD or obstructive sleep apnoea who tend to retain high levels of CO2)
- initial oxygen level is 21% and thus after 12hrs, as each molecule of O2 is converted to a molecule of CO2, this will fall by the same amount the CO2 rises, ie. 2500ppm or 0.25% which will result in oxygen levels falling to a very safe 20.75%
- obviously, as you increase ventilation to outside air, you not only lose the warm air, but you also get wind chill if not covered up - so ventilation is a delicate balance for comfort
Why semi-naked?
- the main reason is to use your body as a 100W heater combined with the electric blanket to warm the tent air
- sleeping semi-naked has many health benefits - see sleeping naked
- finally, you sleep better camping if you can mimic how you sleep at home as much as possible:
- use a quilt or open sleeping bag rather than get cocooned and trapped inside a hot sweaty sleeping bag
- a nice wide quilt or open sleeping bag reduces drafts coming in under it without having to tie it down
- use of the electric blanket helps control warmth, warming the air you breathe with the help of your naked body, and allows you to sleep naked without shivering as long as you can control wind chill and air temperature inside the tent does not drop below around 13degC
Equipment you need
- 1P or 2P well sealed mainly fabric inner freestanding tent (which can stand without use of fly or pegs if using a 4P tent as well) - see comparison of full fabric 2P and 3P tents for colder nights
- NB. normally sealing up your small tent will result in condensation from your breathing and is the wrong thing to do if you don't have an electric blanket however if you keep it warm then this will be much less likely
- a mattress with a high R insulation rating of at least 3-4 to insulate you from the ground
- a stretcher bed to elevate you - warm air rises so you will be much warmer half way up your 2P tent than on the floor
- 12V LiFePO4 battery - preferably at least 100AH (you will probably use 25-50Ah per night) - see 12V batteries and battery boxes
- 12V 50-75W electric blanket (which does not have a mandatory automatic off after 45min) to lie on (at least 50W, preferably a 75W one with ability to quickly drop down to 50W) see 12V heating pads / "electric blankets" to lie on
- my preference is the ElectroWarmth T36 mattress pad but these are hard to come by.
- a travel blanket or similar to place over the electric blanket to keep it clean
- a quilt / open sleeping bag to cover your lower legs as these are more prone to suffer in colder air, and also in case you do get cold or have a battery failure, you have a backup to keep you warm
- pillow
- thin balaclava for your head is nice (or better still a U-shaped foam neck support with built-in hood)
- perhaps thick dry hiking socks but these are probably not needed
recommended extras to get that extra warmth
- a 4P tent to put the 2P tent into to further reduce wind chill if leaving the 2P door open to the air for better connection with nature and easy ingress and egress for those night walks for a pee
- in this case you do NOT use the fly of the 2P tent, nor do you peg the 2P tent down
- example MacPac Apollo 2P tent fits nicely inside a 4P fast frame tent such as that by Oztrail
- a stretcher bed to elevate your body off the ground and higher into the 2P tent's heat gradient
- a self inflating mattress to go between the stretcher bed and electric blanket adds comfort
- an insulating blanket to place over the 2P inner canopy if it is being used inside a 4P tent for extra warmth retention
- 12V 10A+ car demister heater to rapidly warm up the tent when you get in it (but it will run your battery flat quickly so don't be leaving it on too long!)
- 0.1mm thick clear PVC sheet (eg. 1.5×2.4m) which can be clamped to each side of your 1P or 2P tent to stop wind chill but allow you to have visibility out so you can be more bonded with nature and the camp experience
Site selection
- the main needs in addition to usual tent site selection criteria are:
- orient your tent door opposite in direction to the wind direction for that night to give the best chance of reducing wind chill
- ideally the tent door should also face AWAY from other campers if you wish to have the tent door open or only meshed for privacy
- finally, if you plan to have a open door or mesh door it is important not to be downwind of any drop toilets or the smell will make your sleep unpleasant - that means you will want your tent sited BETWEEN other campers and the drop toilets but the door facing towards the toilets for privacy from the other campers.
Variations on the theme
the confident open door approach
- this is obviously not for everybody nor for every circumstance
- it is critical that wind is minimised from entering the tent door - having a 2P tent inside the 4P tent further adds to the ability to reduce wind chill into the tent
- works well in winter when there are almost no insects around and few animals that would enter your tent (animals generally won't come into your tent if they can't smell any food or other smelly objects - not even possums, although wombats may still try!)
- you need to trust other campers will not attack you - make sure they know your boundaries and you can trust them!
the department store heat wall idea
- department stores with large open doors keep the cold air out by creating a “wall” of warm air at the entrance - warm air has higher pressure than cold air so the cold air doesn't come in much.
- a similar approach can be used by having 6“ or so of your electric blanket closest to the open door create this area of heated air column
- my experiments show that lying naked on an electric blanket at around 50W combined with the 100W of naked body heat without any covering, can maintain a 2P tent interior at 13degC (15degC at the ceiling) even though the outside temperature is just 7degC and the door is open and the electric blanket ensures there is no need to shiver while the warm 13deg air temperature makes breathing so much nicer
added benefits of this approach
- better visibility of the outside world and the stars for better connectivity and better situational awareness
- no noisy zips to find and undo that disturb fellow campers when you need to get up during the night
- faster egress if disaster happens (eg. tree falls or tent catches fire)
- less flatus trapped if you happen to drink a half a dozen beers that day, the substantive methane flatus load will not be trapped inside a small closed space in which you need to breathe!
- no condensation inside the tent thanks to the warmer air
- if the wind does pick up, you can just either:
- close the door for more warmth, or,
- turn up the electric blanket heat setting if available, or,
- if you really need to, cover yourself with a quilt but this may lower air temperatures and make you too sweaty unless you turn off the electric blanket
problems with this approach
- other campers can be an issue
- in mosquito season you need mosquito protection
- you need to minimise wombats and bullants entering
- in areas where nocturnal animals are a concern including spiders you may feel safer with at least one barrier - this could be the mesh door of the 4P tent or the mozzie tent!
the almost fully enclosed 2P tent
- this may suit those more paranoid about risks from outside the tent - although it is a bit like putting your head in the sand as you can't visualise what is happening in your surroundings and sound directions can be confusing inside a tent
- this allows greater warmth as there is less cold air entering and less heat escaping hence you can use less power
- the warm air will still prevent tent condensation and allow comfortable warm air breathing