A 33g alpine over-night sleeping bag warmer

[telemarktim]

If you have slept in a small tent in the snow or in very cold alpine conditions you would appreciate that a small source of supplementary heat in your sleeping bag is so very welcome, particularly if it is strong at the start and persists all night.

If you also wisely store your water in your sleeping bag to stop it freezing overnight, it might as well be turned into a hot water bottle. It will give you heat rather than taking it from you. Water at a given temperature can store about six times as much heat as the same wight of rocks, so it makes an excellent and comfortable heat bank.

I have used one of my backpacking water bottles (2 L vinegar) as a hot water bottle with success. The plastic withstands 100C water and the lids seal very well. I filled the bottle with water that was heated with the abundant heat from an efficient wood burning tent stove. To see what I am banging on about see the photo and the link below:


https://timtinker.com/the-kiss-tent-stove-for-alpine-tent-heating/

The hot water soft bottle. I purchased some 2L soft bottles to experiment with to see how these flat 33g devices would perform as soft hot water bottles for winter camping.



They can hold 2L of boiling water and so far they have held up well to the 100C water callenge.


When wrapped in an experimental insulating cover made from a small hand towel the outside temperature was a pleasant temperature for providing supplementary warmth in the Goldilocks reange.


I have tested the soft hot water bottle for 7 nights in a cold unheated room and it provides more than 12 hours of pleasant warming that should be of comfort to alpine campers on those extra cold nights.

The next step in the project will be to devise a lightweight cover that will give the optimum, or even a variable, release of heat during the sleeping period.


Addendum 1.- Hot soft bottle cover
Here is the cover that I made out of bubble-pack (silver coating both sides). I found that my ‘blister tape’ from my first aid kit bonded strongly and made the cover easy to assemble.
This cover leaves the surface warmer than with the experimental towel cover and, as would be expected, it cooled down quicker, but still provided 8h of stronger sleeping bag warmth. "This is more than enough for any self-respecting skier/snow trekker!" An insert of an extra folded sheet of bubble-pack could be used to reduce the surface temperature if ever needed.

The cover weighs (34g) as is almost the same as the soft bottle (33g). So the 'ultralighties' among us may be doubtful about doubling the weight of this little luxury.





I will also test a sealed cell foam cover to see how it performs.



For more details on the project please see:
https://timtinker.com/hot-water-soft-bottle/

Tim

[ChrisJHC]

You can also use a spare pair of socks as a cover.
You may already be carrying them so no extra weight.

[telemarktim]

You can also use a spare pair of socks as a cover.
You may already be carrying them so no extra weight.

Hi Chris, Yes, I do this on my yacht and slip a PET soft drink bottle hot (much less than boiling) into a sock. PET will not cope with boiling water. The 2L litre soft bottle that gives the 12h warming will not fit in socks, or at least not my socks.
Thanks, Tim

[telemarktim]

Addendum 2 for the alpine overnight sleeping bag warmer

I made a liner for the soft bottle cover by folding in two a scrap of bubble-pack (16g). The original cover was designed with a little spare space to accommodate the liner. The folded side of the liner was fed down into the cover and the soft bottle was place within the liner.



The idea of the liner was to reduce the surface temperature of the cover a little when the soft bottle has been freshly filled with boiling water. It did initially reduce the surface temperature, as expected, so that it was more comfortable for direct skin contact. I think that it would have also extended the duration of very strong heating for several hours, but I was sleeping and unable to monitor the change.

Under extreme snow camping conditions, when extra warmth is so welcome, the liner could be removed from the cover, partway through the sleep period, to provide greater heat transfer when the water temperature has dropped considerably. Similarly, the outer cover could eventually be removed to enjoy the direct heating of the soft bottle in the wee hours of the morning.

The extra 16g liner weight may be worthwhile, and if nothing else it will make the device a more comfortable substitute 'sit-upon' with a total weight of 50g.

[Moondog55]

It's a great idea for when you have marginal gear but if you have to resort to doing this constantly in white season you really don't have the correct gear for the conditions.

[telemarktim]

It's a great idea for when you have marginal gear but if you have to resort to doing this constantly in white season you really don't have the correct gear for the conditions.

Hi Moondog55, I am not talking about having suboptimal gear. You have a stove in your tent and that does not make your gear suboptimal. I think you would agree that the extra warmth is enjoyable and rewarding after a big day of skiing.
Tim

[Moondog55]

Only have a stove for basecamping tho.
I often fill a bottle with boiling water and insulate it overnite but mainly to give my morning coffee a head start in the AM or to keep my ski boots from freezing solid.

[telemarktim]

H Moondog88, See we are on the same page. If a 400g tent stove can go backpacking skiing with me why not use it for a little extra comfort for an old body. Tim

[telemarktim]

An update on the hot soft bottle.
On the night that I reached 50 fills& warm sleeps, a tiny leak developed. Less that a ml/h as shown in the photo below.



With nothing to loose, I did a simulated accidental rollover or the Bargearse Test (in a safety spill bag) and the soft bottle held up quite well, although the dog was not so sure. The video of the test is below.


Tim

[BarryK]

Ha ha, this is totally OT, but the word "bargearse" triggered an old memory:

https://www.youtube.com/watch?v=Fahf77qzEnE

For those who don't know, "Bargearse" is dubbed, sendup of a 70s Aussie cop show named "Bluey".

My apologies, couldn't resist posting this. Will delete it if anyone objects!

[telemarktim]

Ha ha, this is totally OT, but the word "bargearse" triggered an old memory:

https://www.youtube.com/watch?v=Fahf77qzEnE

For those who don't know, "Bargearse" is dubbed, sendup of a 70s Aussie cop show named "Bluey".

My apologies, couldn't resist posting this. Will delete it if anyone objects!

Barry, Please don't apologise. I thought Bargearse was very funny and your youtube link shows that it still is. I also thought it was a fair name for the final pressure test!
Tim

[Orion]

The hot water bottle trick is an old one. It works, although leaks are an obvious concern. But it's not particularly weight efficient since good goose down weighs a lot less than petrol or ethanol on a trip of more than a few days. I think of it as kind of a band-aid to poor planning. It's always better to just have a warmer bag/quilt.

[telemarktim]

The hot water bottle trick is an old one. It works, although leaks are an obvious concern. But it's not particularly weight efficient since good goose down weighs a lot less than petrol or ethanol on a trip of more than a few days. I think of it as kind of a band-aid to poor planning. It's always better to just have a warmer bag/quilt.

Hi Orion, You are forgetting that I burn sticks to boil the water and I am not so silly (and inefficient) as to carry my fuel over multiple days. I also have a great down sleeping mat and a good sleeping bag. If you are experienced at sleep in the snow you would know that a little extra warmth is always welcome. Tim

[Orion]

Hi Orion, You are forgetting that I burn sticks to boil the water and I am not so silly (and inefficient) as to carry my fuel over multiple days. I also have a great down sleeping mat and a good sleeping bag. If you are experienced at sleep in the snow you would know that a little extra warmth is always welcome. Tim

I didn't know you burned sticks. Most of the time that's not a viable or even legal option for me. I personally would rather just get into a nice toasty bag and not worry about extra warmth but I mostly visit a range (CA Sierra Nevada) that doesn't get particularly cold or damp in the winter. Typically it's around 10°F/-10°C at night. Not a big deal. I build a fire about once every 15 years.

[telemarktim]

Hi Orion, You are forgetting that I burn sticks to boil the water and I am not so silly (and inefficient) as to carry my fuel over multiple days. I also have a great down sleeping mat and a good sleeping bag. If you are experienced at sleep in the snow you would know that a little extra warmth is always welcome. Tim

I didn't know you burned sticks. Most of the time that's not a viable or even legal option for me. I personally would rather just get into a nice toasty bag and not worry about extra warmth but I mostly visit a range (CA Sierra Nevada) that doesn't get particularly cold or damp in the winter. Typically it's around 10°F/-10°C at night. Not a big deal. I build a fire about once every 15 years.

Hi Orion, That is understandable. However, we often camp in our alpine regions where it is often very cold. The stick burning is not in an open fire, but in a tiny and efficient closed slow combustion wood gasifier stove that burns only 400g/h of little dead sticks. It has a heat output of about 1000 watts. It provides cooking, snow melting and tent warming when the warmth of the skiing activity is over. The hot water bottle is just a nice little extra comfort that makes the winter experience more enjoyable for the extra weight of 33g. Here is an example of the little stove in the link below:
https://timtinker.com/the-kiss-tent-stove-for-alpine-tent-heating/

Tim