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Using hot water bottles as 'cached heat'
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Kevin Burton
(burtonator) - F

Locale: norcal
Using hot water bottles as 'cached heat' on 12/19/2012 01:43:06 MST Print View

This is a trick I've been using for a while with pretty solid success.

I thought of it independently but hammockforums has a sticky about it and it's a bit thread there.

Wood is essentially cached energy from the sun. When you're burning it you're essentially releasing the energy stored 30 years ago.

The problem is that it just shoots up in the air and is vanished.

You can temporarily cache/store some of this heat in water. I usually heat 1L *just* before it boils (so that it doesn't create a gas) then poor it in a 1L platypus bottle.

Then I throw this in the bottom of my sleeping bag.

It works GREAT for the first half of the night but about half way though... roughly 4 hours it is somewhat luke warm.

I was thinking that if I had a SECOND 1L bottle on the standby then I could swap it in. The problem is HOW do I do that?

I was thinking that one could have a small insulating container JUST for this purpose.

You could keep it outside of your tent and have it store say 3x 1L bottles that you can bring into your bag anytime you want more heat.

You wouldn't want to put ALL bottles in at once because it would be too hot and also they would start to fade after about 4 hours.

Also, storing 3x 1L bottles next to each other means there is less surface area for the heat to escape so they may last longer.

It could mean much warmer nights and actually a way to pack in LESS weight since you could get away with less down.

I already carry at LEAST 2 bottles now. Adding 2 more won't be significant weight.

Travis Leanna
(T.L.) - MLife

Locale: Wisconsin
Re: Using hot water bottles as 'cached heat' on 12/19/2012 02:15:55 MST Print View

Using a warm/hot bottle is a trick to stay warm, yes....but I have some reservations...

Before I go into my post, I'll start by saying that I haven't done the math for it all, so I dont know exactly how it works out weight-wise.

Its true that platypus bottles do not weigh much. 2 extra 1 liter bladders will weigh about 3 more ounces. Then you need an insulating container for the bottles. Dunno the weight, but I'd guess at least 8+ ounces to be of any use, especially in cold climates when you'd actually need extra warmth. You also need to heat the water. If you use a fire, then you're not really out any extra weight, but if you have to use fuel, then you're talking an ounce or so per night. If you have to melt snow, then there's more fuel used. Then there's the hassle. Time and energy is used by you to collect, heat, and store said water.

So to do all of this, we're talking at least another pound of weight (depending on fuel and trip length), plus the need to do so. Would that weight not be better served in your insulating pieces such as your sleeping bag or pad?

I don't mean to disparage your thought, but I do question the practicality of it. If there is proof to the contrary, I will happily retract my doubts!

Franco Darioli
(Franco) - M

Locale: @Tarptent
Using hot water bottles as 'cached heat' on 12/19/2012 03:15:17 MST Print View

The only way to have hot water (in freezing/sub freezing temps) 4-6 hours after boiling your water would be to use a vacuum flask..
An insulating container will not be better than your sleeping bag plus you in keeping the water warm.
You can get a 1L flask for about 17 oz or so, but of course that weight in down will keep you just as warm if not more so.
(add to that the extra fuel and the air that escapes your bag when performing the change...)
So the idea here would be to start with your standard bottle inside your bag , then when you wake up you transfer the water from the flask into another bottle and put that inside the bag.
If nothing else you have water in the morning...
BTW, an easy way to test insulating containers is to use your fridge (40f) or your freezer (0f)

Steven McAllister
(brooklynkayak) - MLife

Locale: Atlantic North East
Other insulation on 12/19/2012 03:38:59 MST Print View

You could do two bottles at once before you go to bed. Put both in some kind of down layer, booties, vest, ... inside your bag/quilt when you go to bed. It wouldn't initially be as warm, but may extend that warmth into the colder part of the night.

I don't know how much it would last and besides who can spare down layers on cold nights?

Derek Goffin

Locale: North of England
Using hot water bottles as 'cached heat'" on 12/19/2012 06:08:28 MST Print View

This need hardly weigh anything. If you carry a 1 litre platypus already, if you use a cosy to keep food warm while it rehydrates and if you have spare mitts that you are not using whilst sleeping.
Put near boiling water in the platy. I put boiling on 200ml of cold to keep the platy a bit cooler. Stick the platy in any mitts that are spare, plastic bags may make this easier so mitts slide over mitts. Then take your cosy which you have remade from sleeping mat foam to be an envelope for the platy too. Put the mitts and platy in the foam, close the lid. If you have a spare dry bag whilst camped put it all in that. The bottle will stay warm for 7 hours and in the morning you can unwrap it ot let out the last heat. Then your first drink is half warm in the morning.
If you are concerned about laying on the platy and bursting it, the dry bag will save the day. This accident has never happened to me but it is clearly possible.
The extra weight is your foam cosy less your old cosy and about half an ounce of gas per use. If you had to melt snow you would have had to anyway for your morning drink.
Our foam cosy weighs less than 1 ounce and doubles as a sit mat.

Edited by Derekoak on 12/19/2012 06:13:17 MST.

Jeffs Eleven
(WoodenWizard) - F

Locale: Greater Mt Tabor
Re: Other insulation on 12/19/2012 08:46:31 MST Print View

Seems like a lot of trouble and highly variable results, and potential fuel waster. A chemical hand warmer would be much easier/ reliable... although non-multiuse.

Another 2oz of down in the bag?

heat on 12/19/2012 08:51:36 MST Print View

rocks warmed near a fire work OK too, no limit.
In the days before furnace heating, this is what people did inside their houses at night to pre-warm their beds.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Using hot water bottles as 'cached heat' on 12/19/2012 09:52:02 MST Print View

I'd suggest, if you want to use more bottles, to put ALL of them in your sleeping bag, perhaps with a sweater wrapped around them so they yield their heat more slowly. That will be a warmer environment for the second bottle, by far, than anywhere outside your sleeping bag.

But, as others have said: for 1 or 2 nights, chemical handwarmers in each sock will weigh less, take no fuel, work better nad last all night. For longer trips, bring a warmer bag.

I feel more strongly about mornings - waiting for the water to boil cools me off more than the BTUs I get from a hot drink. I prefer to just get up and get hiking. But I suspect some folks make the same mistake at night - staying up late while inactive around camp, cooling a degree or two (core temp) which takes a LONG time to recover from - perhaps not until you are hiking the next day if your sleep system is marginal for the conditions.

Daryl and Daryl
(lyrad1) - MLife

Locale: Pacific Northwest, USA, Earth
Re: Using hot water bottles as 'cached heat' on 12/19/2012 10:16:10 MST Print View

My wife recently returned from a trek in Nepal and they used warm water bottles for sleeping. They didn't replace them during the night, however, so it only addresses your existing use... not your replacement idea.

Kevin Burton
(burtonator) - F

Locale: norcal
wood fire. on 12/19/2012 10:22:50 MST Print View

I forgot to mention that I almost always use wood fires so packing in more fuel won't be an issue.

It MIGHT be a good idea to experiment with using a neoprene or foam cozy for the 1L bottle and keep it in the sleeping bag with me.

Maybe just some blue foam wrapping the platypus bottle.

That might extend it a bit more and last into the morning.

The cozy could also double as a sit pad...

Ben Crocker
(alexdrewreed) - M

Locale: Kentucky
Water bottles on 12/19/2012 10:33:47 MST Print View

Its usually coldest just before the sun lights up the sky. It seems by then the water bottles are likely of little use. If you possibly could keep them warm over a long winter night, it seems that the best place would be inside your bag. That's likely the best insulation you're carrying and I can't see any reason not to keep it in there.

I would agree with the alternative of carrying a warmer bag.

I don't know much about the hand warmers. How long do they really last? I guess you could wait until late at night to start them easy enough. Are the chemicals in them bad stuff?

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Hand warmers on 12/19/2012 12:26:57 MST Print View


The non-reuseable hand warmers are cloth packets with iron fillings, salt, water and cedar savings inside. The iron rusts when exposed to the air and that generates heat over 8 hours. We use them in the kids' boots for downhill skiing when it is under -10F.

They are about $2 normally, $4 at the shop at the ski area, but I stock up when Sierra Trading Post (1) has them on sale, (2) I have a 25-30% off coupon and (3) I'm ordering other stuff. Then they are 40-60 cents each and I order a few dozens of each type (hand, foot, etc).

Ben Crocker
(alexdrewreed) - M

Locale: Kentucky
Hand warmers on 12/19/2012 12:39:56 MST Print View

I suspected you would know the answer to that, David. So they don't really have anything too bad in them it sounds. Good to know.

Kevin Burton
(burtonator) - F

Locale: norcal
Re: Hand warmers on 12/19/2012 12:49:43 MST Print View

This is pretty much the ONLY way an ultralight backpacker is going to carry IRON !! :-P

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Hand warmers on 12/19/2012 12:59:10 MST Print View

The non-reuseable hand warmers work OK as long as the packets are well-sealed to air. One guy carried many of those packets on a cold expedition with the intention of using four or five per day. Well, either the packets were old and stale or else they leaked air. Less than half of them worked at all.


Tim Zen
(asdzxc57) - F

Locale: MI
Re: Using hot water bottles as 'cached heat' on 12/19/2012 15:41:42 MST Print View

I recently used an under a year old 1L, Nalgene Canteen (fold up kind) for a hot water bottle.
It delaminated at the top where the sides are welded to the screw top area and sprung a leak.
I am in a discussion with Nalgene about it, but at $9 bucks, I am not expecting much.

Specs say it can handle 102C. I did not come close to that temperature.

Franco Darioli
(Franco) - M

Locale: @Tarptent
Using hot water bottles as 'cached heat" on 12/19/2012 15:45:33 MST Print View

BTW, I am fully aware that I am beating a dead horse but I still don't get why folk don't try these sort of things at home first ....

Michael Cheifetz
(mike_hefetz) - MLife

Locale: Israel
Testing on 12/20/2012 07:00:54 MST Print View

@Franco - dunno if you are talking about the bottle delaminating or the chem stuff not working...but of course you are right.

the bottle is pretty easy to test beforehand

what I would do with the hand warmers (this is what we did in the army) is buy a bunch from the same batch and test one or two before each trip + visually inspect the ones you are taking just to make sure no nicks or holes in the packaging

@Kevin - if you have a fire going..why dont you put a rock in it and then later during the night you can take it in the bag (of course wrapped in something like a fleece)- the advantage here is that the fire will ostensibly keep the rock warm for quite a while...


eric chan
(bearbreeder) - F
hawt nalgenes on 12/20/2012 07:11:04 MST Print View

i am a fan of hawt nalgenes, but do not use them to reduce the weight of the down ... the reason they work so well in winter is that you are going to spend the fuel to melt the ice/snow anyways ... in cases where you dont need to melt, they are useful as an EMERGENCY measure or where you have boiled water to purify it, etc ....

bring the appropriate insulation for the temps you expect ... and then use the hawt nalgene should it be colder than expected

Gregory Stein
(tauneutrino) - F

Locale: Upper Galilee
Use of chemicals is an acceptable option? on 12/20/2012 07:33:40 MST Print View


If you mix some potassium permanganate with sugar and add water (or snow and shake), then this mixture will be hot in 1-2 minutes. I've done it at my home lab (yes, chemistry was one of my hobbies).

Not sure what to do with the chemicals after that... Not that eco friendly maybe...