« The Printed Website: Volume III & The Comments | Main | How to Build a Practical Household Bike Generator »


Feed You can follow this conversation by subscribing to the comment feed for this post.

Will K


How long does a typical rubber or pvc stay long for, if filled with 60c water?

Michael Lipkin


awesome. if you boil a 2/3 full kettle and top up with cold water before filling the bottle you get about the right temp. No need for thermometer



I live in a very (!) old family house house in north-east France, near the belgian border, and even though the house has been partially equiped with a central heating system, heating the place as you would heat a modern house simply isn't an option (unless you don't mind burning A LOT of heating fuel). As a consequence of that, HWB have always been the house standard when it comes to thermal confort during night time when a thick sweater and a scarf usually fixes it during the day. I did find a new interesting use for HWB, though : I've recentlly started homebrewing and my fermentation chamber (aka: the closet) lacked a couple of °C during the night, when the central heating system is turned off. I was afraid that this might screwup my fermentation process so I quiet naturally thought of wrapping the 5L fermenter into a couple of blanckets with a HWB stuck next to it and wrapped itself in cloth to allow a slow night long heat transfer and avoid overheating. Did the job perfectly!"

Thanks. Great article.

kris de decker


@ Will K

That depends on the environment, but in my case they stay warm for roughly two hours. Under a blanket they stay warm for longer.

Loads of comments on hackernews: https://news.ycombinator.com/item?id=30023681



Hi Kris, thanks for the insightful article.
What's your opinion on heat pillows? Like cherry stone or rice pillows? If my calculations are correct, heating one in the microwave is even more efficient than heating the water for a water bottle. Heating in the oven is probably pretty inefficient although I can imagine tossing the pillow in after cooking and not heating for the pillow specifically would help.
Additionally, heat pillows don't wear as much as pvc/rubber bottles and there's no waste associated with their use. They can be produced from scrap fabric and food waste (cherry stones) or other organic materials, limiting waste potential in the production chain.
I'm curious to hear your thoughts.

Hugh R


In New Zealand, at least until the 1950s, some hotels would put hot water bottles in guests' beds while they dined. A well understood local custom when central heating was not common. My parents, staying at one hotel, were startled as they returned to their room to hear very loud noises, beating, and shouts coming from a nearby room. The reason? An American guest, returning from dinner, and seeing a suspicious lump in the bed, believed it was a snake and was attacking it with a golf club. The bottle burst and he now of course had an amused audience and a soaking wet bed.

A Kalkman


Very funny piece of info. I am 71 years old and use the hwb already for 50 years. I bound one on my back once when I was working as an upholsterer and had a backache. It brought me through the day. I use a very old rubber waterbottle allredy more than 20 years old. I will google and try and find the Japanese one. Thanks again very much for this interesting
piece of information. From Holland with love, Ans Kalkman



With the Boy-Scouts we used to heat bricks in the camp-fire and then carefully roll them in newspapers and blankets; kept us warm even during camping at -5C or worse.

My mother had a few copper hot water bottles made from old WWII canon-bullets. I still use 1 or 2 plastic hot water bottles in Portugal during the cold season, typically 3 months... Enough to avoid heating the whole house. Together with thick blankets it keeps the costs of winter to a minimum.



One alternative to the hot water bottle which is often used in Switzerland is the "Cherry Pits Pillows"/"Cherry Pits Bags". Cherry pits, which you can easily gather with a cherry pitter when making preserves, (and I assume previously mainly from distillery waste as each farm was distilling all kinds of fruits) are cleaned and dried. Then, you sew them in a bag, and put them into an oven. There was a space for backing and heating up stuff in each farm kitchen when people cooked with wood, but the modern electric oven or even microwave work as well. Then you use them as the hot water bottles you mentioned. There are commercially available ones, you can find them with the word "Kirschensteinkissen" or "Chriesisteisäckli".

 Will Lisak


I think you neglect here the real original hot water bottle, - the hot stone. The hot stone has been used doubtles for the same purpose since the domestication of fire, but has survived in cultural memory because it does not leave behind a discernible artifact, (a stone looks like a stone) except in the case of the ubiquitous shaped marble and soapstone warmers. Here in Vermont they were placed on or around the stove during the day and taken to bed at night and others were used to put under your feet driving a sleigh or cart or even to stand on if you had a cold outdoor job to do in one place. I use them (the soapstone pieces) and they are truly remarkable in their heat retention.

I've seen old timers around here with soapstone blocks stacked up all over and around their woodstoves, increasing the heat mass and slowing and regulating the heat dispursursion. as an aside, I was asking last year for advice on an efficient wood stove, thinking I might get one of the soapstone wood stoves that are so lauded in the us, and a russian friend said to just stack stones all around my current old iron stove and it would yield the same benefits. I'm not sure of soapstone vs water but the manufacturing and opportunity costs are surely much lower and it's less messy and prone to catastrophic failure.



I was using a 2l plastic fizzy drink bottle filled from the hot water tap and stuffed in my jacket for the frosty drive to work, my car's heater would take ages to warm up and this bottle of hot water made all the difference,

on arrival at work the guy who usually unlocked the gate would often be parked outside because the padlock was frozen, my bottle of water poured over the padlock thawed it in moments,

I also never bought any windscreen de-icer, I'd just have a second bottle of hot tap water and pour it in a line across the top of the windscreen and rear window,

the tap water from a modern domestic hot water system is regulated to a temperature not high enough to cause scalding and in my experience not hot enough to cause frozen windscreens to shatter, the plastic fizzy pop bottle is of course free!

Rolf Bauche



mal wieder ein sehr interessanter Artikel!

Zwei kleine Anmerkungen:

1. In Frankreich werden bis heute "Wärme-Keramiken" aus glasierter Keramik in Ziegelsteinform hergestellt. Eine interessante Alternative, die kein warmes Wasser benötigt und im Kachelofen aufgeheizt werden können.

Siehe: https://koerper-waermespender.de/pages/waermespender.php

2. Das Bild "Foot warmers on the floor of a railway carriage (1929). Source: The History Trust of South Australia. " zeigt meiner Meinung nach Spucknäpfe und keine Fußheizungen. Typisch für Spucknäpfe sind die trichterförmigen Oberteile.

Mit freundlichen Grüßen

Rolf Bauche



Dear Kris,

I’ve been experimenting with similar heat-the-person-methods. I use 17 Watt grow-matts for young plants. They are flat, very comfortable and cheap. I typically use one under my feet (plus blanket) and one behind my back in an office that is kept at 13 degrees.

So I use 34 Watts. This compares with you calculation: every two hour re-heating water from 30 to 60 C requires about 60 Wh and I use 34*2 = 68 Wh of electrical power. However if one heats cold water to 60 C one would use twice as much energy.

The savings in terms energy are indeed immense, and comfort is indeed higher than heating the whole room when I just sit behind the desk.

The great advantage of warm water is that they are more portable, so I will start using these as well.



Sue Rine


I was fascinated to read your article about the history and use of hot water bottles. For 4 years our family lived in a cabin with no power. In Winter hot water bottles were a feature of daily life. even with the fire going there were times when the temperature was below 10deg C all day and lower at night. Each family member had two hot water bottles which we mainly used in bed, but there were also many times when we had one tucked up our jumpers during the day.
We've graduated to a passive solar house and the hot water bottles are now a memory. 😀

Romain Lange



Do we know if hunter-gatherer societies, or the Inuits, use the hot bottle technique ?

I see in this documentary about paleolithic techniques, with bladders used as water bottles. Could they be used as hot water for cold nights ?

kris de decker


@ Will Lisak @ Rolf Bauche
Indeed it seems that I missed part of the story: the hot stone. Great to see this, thanks!

@ Tjitske
Heat pillows are an alternative but hot water bottles can hold more heat.

@ Romain Lange
Could be but maybe stones were more practical.



I love this! I use my 40 year old daughters little pink baby hot water bottle since... 37 years. It's Swiss quality and still totally intact. I always struggle with cold feet and this little treasure goes to bed with me at my feet 9 months a year. I fill it all the way up with quite hot water and it works fine. I also take it on airplanes to keep my feet warm and the hostesses fill it up for me. And yes I can sleep in a much cooler room thanks to this!



PS THANXXX for posting this

Carlos E.R.


There are electrically heated "bricks". They are connected for 5 minutes to the mains (a thermostat automatically impedes overheating), then unplugged and put inside the bed. I assume they are a ceramic body with a resistance inside, put in a metal casing and a wool cover.

Heat last for hours. I much prefer these to the water bottle, which eventually will burst and wet the bed, ruining the night and more.



Try a large cherry pit pillow, cherry pit foot warmers

We use a Water Heated Mattress Pad, basically a small water heater unit, under mattress pad has medical grade tubing running up and down in a pattern. We have an additional fluffy pad on top of the hot water one,to reduce any lumpy feel,works great.

Search for "Navien Mate EQM 350, Queen – EMF-Free Water Heated Mattress Pad – Dual Tempera", the premium $$$,from there you can find cheaper brands,what we have for $135 and up, prices fluctuates,Google "MERRY HOME Water Heated Mattress Pad Topper".

Also something like a Whitby Hand warmer,uses catalytic head burner, no real flame, but it gets very hot, you have to put it in a small pouch, you don't want to sleep with it because of the heat output and it uses oxygen. Will heat 8 hours.

As with anything use common sense, and at your own risk.



"I'd just have a second bottle of hot tap water and pour it in a line across the top of the windscreen and rear window", probably never happened to you, but excellent way to crack glass,in my neck of the woods,I use cold water.

Shane Wilson



I'm surprised you didn't mention the largest hot water bottle of all -- a water bed! I slept on these for years in cold climates and crawling into bed was ALWAYS a pleasure. But, they seem to have fallen out of favor.

Steve Bohne


Yeah...great...until the stupid cap comes off and fills your bed with tepid water. No thanks.



Fill a tube sock with rice, tie a knot on top, microwave it for two minutes, stay warm all night. Reuse for years.



Thanks for wonderful story on hot water bottles.
I once wrote about Human bed warming Services offered in a Hotel. See link:
This was in 2010 - don't know if this continues now!

Wendy E Powell


I was raised using hot water bottles to stay warm. Sixty years later and I still heat my bed and feet with a hot water bottle. I put hot tap water in it for 15 minutes before half emptying and topping up with boiled water. My bottle is tepid temperature when I wake up the next morning (7 hours of sleep). I've gifted water bottles to family and friends and they all love them.



GREAT to see an article about hot/cold water bottles!!! Brilliant!

I use them myself any time I get a bit too chilly but don't want to make a fire... to save time mostly and gain comfort.
My house is wood heated. Making and tending the fire (not to mention gathering the wood and all that entails) is a very time consuming process!

Fortunately the house has solar power. So often I simply heat water and fill a hot water bottle rather than make a fire...IF my hands are not too cold to function. That is the line for me. I love to do art and my hands must be able to move.If the hot water bottle does the trick that is all I need.

The challenge with the hot water bottle for me is being able to walk around with my hands free to function rather than holding onto the bottle. With the bottle tucked between layers of my warm clothes, and moving around, how to keep the bottle from falling out is the question. I have tried wearing a belt over the clothes just below the bottle level. That sort of works. I have tried a soft rope that went through a hole in the lip of the hot water bottle tied around my neck. This sort of works too. But neither is very comfortable. Suggestions?



Oh, I forgot to add to my first comment, my grandfather, who grew up in South Dakota in a SOD HOUSE (!)...must have been in the late 1800s...would go to school on a horse drawn sleigh in the wither. To stay warm they had a big round rock that had been heated in the fire then wrapped in a buffalo skin. The children huddled around it on the way to school.

On my wood fire stove I keep a pot to heat water for dishes or what ever. If that fire is going, rather than bother with the water bottle, I use 3 fire bricks that are always on that stove. I can take a brick for my feet or lap and rotate them to keep the warmth up. I put one at the base of my bed before going to sleep and take one with me for my arms. My sleeping room is never heated, so the bricks or water bottle do save energy and make the bed quite comfortable.

Pawan Kumar Gupta


Despite electricity operated tell bottles, the hot water bottle (water in a rubber bottle) is still very common in India. They offer much better thermal comfort to body in winters. Often used to sooth the painful joints or troubling veins in the legs.

Mark O'Connor


Years ago when I looked after an old farmhouse in Italy, the inside temperature at night in winter was often below freezing. I found that one hot-water bottle would be cold and useless before morning. But two bottles, placed back to back and wrapped in a double-bed sheet, were as good as another human in the bed--still warm in the morning. A tip worth knowing!

Tomislav Plechinger


Another great article!

Just a small typo that I noticed - not "Croation" but "Croat".

Thank you for spreading the word about the little-known but very prolific inventor, the great Eduard Penkala.

Greetings from Croatia!

Jenny Matthews


Kris you should head up a climate change conference because we're going to need all the help we can if the targets are going to be met - which they're not at the moment, and time is running out. We were invited to a garden supper in Mallorca in January - zero temperature - the table had a massive blanket over it, big enough for 6 people to tuck around their hips, and with the 1 bar electric heater under the table, we were very toasty nearly up to our waists - thermal tops etc. kept our top halves warm, and we enjoyed a great supper very comfortably. I guess hot stones would have done the job equally well.



I guess that today a microwave oven will be convenient for reheating the bottle.

Sweden does not have a strong tradition of hot water bottles. In upper class homes coal heaters were probably used in the 18-hundreds. Warm water bottles would often be insufficient here and houses should be properly insulated and heated. There are stories of people in the country side sometimes keeping it real warm (25-30 degrees perhaps more) inside in the winter time in areas where firewood was one of the few commodities available in ample supply.

In the last couple of decades pillows filled with wheat that should be heated in the microwave oven have been marketed as warmers. Perhaps more against aching body parts than for sleeping. The heat capacity would clearly be lower than for hot water.




Many African safari camps place hot water bottles wrapped in towels in your bed at night (nights can be cold!). On her first safari my partner crawled into bed and pushed her feet up against the hot water bottle. She shrieked and jumped up, thinking some African critter had crawled into her bed. We now use hot water bottles in bed in the winter so we can keep the room cool but our feet warm.



All through my childhood, we used a red rubber HWB. It never burst, over a period of some 20 years, and there was never any talk of its needing to be replaced because of fear that it might burst. The first HWB I bought after returning to the US following a decades-long stay abroad burst and flooded the sofa on which I was using it. What a shock!
Why are there no long-lasting rubber HWBs on the market today? Experience tells me they should be possible. I suspect that companies find it in their interest to force people—on pain of burns or flooded beds—to buy new ones every 2 years or so, and how I resent that!



My father grew up in Montana in the 40's and his parents were ranch hands (employees on a large ranch). He had a long walk to his one-room schoolhouse down the snowy roads and he said in winter his mother would give him two hot baked potatoes for his pockets to keep his hands warm, and then that would be his lunch.

Ulrich H


In northern Germany hot water bottles are a common household item. I'd expect roughly 10-20 of the population, mainly women, to use them regularly, during their period, for stomach-aches, or for being cold. Also, sacks filled with cherry pits, heated in the microwave with a glass of water, are used for a tight neck or back, or also to add some heat during cold nights if the blanket is too cold.

Interesting, that apparently in other places they are not that common at all.



There is one other thing, you can do with hot water:

Make Tea.

If you have an infrastucture of Samowars, the uttility would greatly increase, if you could use that hot water to make tea.

Public Samowars filled with potable water, have the advantage that you do not need to bother with recycling the water if the people can drink it.

Of course the problem of providing the people with clean drinking containers would come up.

But Hydration is one of the major concerns for the homeless.

So even a public fountain with cold, potable water would improve their situation.



I live in Melbourne, Australia. I have always been very fond of hot water bottles, and far prefer them to electric blankets which I find quite uncomfortable. Another use for them that I worked out a few years ago is to fill them with water and place them in the freezer in summer. They are great to put in your bed on a really hot night. They cool the sheets down beautifully.

I lived for some years right in the city, and there were many homeless people. Melbourne's winter temperature can be quite low, and many nights are under 5C. The wind chill factor makes the temperature lower. In the really cold weeks of winter, I would take out filled hot water bottles at night for people sleeping on the street. I had an agreement with some of the local 24 hour convenience stores that they would allow people to refill them. As you could imagine, the bottles were very much appreciated. I sometimes tucked them in with people who were already asleep, making certain that they weren't touching bare skin of course. I hope it helped them feel as if someone cared.

I have sustained burns from hot water bottles when sleeping with them when drunk! It's amazing how much damage they can do. I tend not to do that nowadays, and I also prefer bottles with covers as they are more comfortable to use and stay hotter longer. I have a couple which have amazing covers and actually stay warm all night and well into the next day, which is great if you are in bed with a cold or something.

When I first set up my facebook page and I was asked during set up what I liked, I didn't know that it meant I could like pages. It was winter, so I just said hot water bottles. Nothing happened, presumably because there were no hot water bottle appreciation pages. Maybe there are now!



You are wonderful. For decades, nearly impossible to find rubber hot water bottles unless one wanted to douche. I think they are still nearly impossible to find. I treat mine better than I do myself. All praise to you. Maggie

John Cliff


While serving in the army during a German winter a great way of keeping warm while traveling on a 432 APC was to sit above the engine cooling louvers. It was wisest to rope yourself on, just in case of falling asleap. The hot airblowing out of the louvers would blow the snow away no matter how heavy it was comming down.



Good article. However, a word of caution. Just before Christmas my partner burned her left ankle, badly, when her HWB burst. She is still having the burns treated.

The HWB had worn through on the shoulder and finally gave out, not on the seam or neck. We only realised how worn it was when we removed the fabric cover- it was her favourite Teddy Bear one- nothing was showing on the cover. Please, occasionally, take the cover off and check the actual bottle for wear.



I own (and frequently use) a metal Japanese hot water bottles as well as a pair of rubber bottles. While both styles do an excellent job of keeping me and my bed warm, I prefer the Japanese one over the rubber version.

Despite being rigid, meaning it can feel uncomfortable depending on where you put it, the metal version retains heat noticeably longer than the rubber version. I sometimes heat water on the stove to about 150 F, put it into the metal bottle, stick it in my bed anywhere from 30 to 60 minutes before bedtime. In the morning, the water is still quite warm if not hot to the touch. (I haven't checked it with a thermometer, but an educated guess would be around 110 F, no more than 120 F.)

Last comment: As someone else mentioned, cloth covers are mandatory, especially| with metal hot water bottles.

Aynsley Brown


For at least the past 30 years, I have been heating our HWBs in our microwave.
Heating on full power for 5 minutes works perfectly. Just make sure that the bottle can freely rotate in the oven and heat up evenly.
HWBs that have brass screw threads in the neck funnel should be avoided.
Rubber bottles are to be preferred, they seem totally unaffected by the microwaves.
Some plastic-material bottles can develop hot spots in the wall of the bottle and locally melt. This is probably because some plastics seem not to be as 'transparent' to microwaves and can get heated in local spots, to the deterioration of the bottle.
The great advantage of heating the bottle in this way is that the same water can be used over and over again.



I love my HWB - great article, thank you and warm wishes to all users

Deborah Lindley


I started making hot water bottle carriers last year to keep people warm working from home and meeting friends outside in winter lockdown www.deborahlindley.com I barely take mine off.



A friend mentioned a great use for hot water bottles.
She used to have to spend a lot of time waiting in her car while her children played football, etc. Instead of freezing or leaving the car running, a hot water bottle kept her toasty and she read away happily while she waited!



Thanks for this excellent article. I grew up reading Walter Hottle Bottle stories https://www.lookandlearn.com/characters/character.php?c=walterhottlebottle and still use one every night x

Benoît Gingras


I'm a newcomer to this site, it's absolutely great. Special mention to
the illustrator and her illustrations for this article, my girlfriend
and like them a lot! They are funny and the lines are beautifully drawn.

Thanks for suggesting the use of hot water bottles. My flatmate told me
about this very article. We live in east of province of Quebec (Canada)
in countryside and I am eager of giving a try to this idea. I would like
to try using hot water bottles under the low table in the living room
covered by a cloth or blanket. The idea of cold bottles in the summer
might be a good idea for me too. I am really weak under high



Benoît Gingras


PS. I forgot to mention that this article reminded me of friends hearing
a man in Yukon saying that he boils eggs and then keep them hot (in
their shells of course!) in his pockets while going outside. It provides
some heat to your hands and minimal heat to your body and you have a
healthy and useful snack on your way!




Interesting article.

I think you should have a look at Camelbaks. They're basically hot water bottles worn as a backpack, and they have a tube to drink from them. This solves the issue of reusing the water.

They're quite popular for people skiing or doing other kinds of outdoor sports, keeping you warm and hydrated at the same time.



I have been using small NATO ammo cans (metal boxes with sealed lids) 1/3 to 1/2 filled with tealight candle wax as a hot water bottle substitute. I place them on low heat on an electric stove until all the wax is liquified, which is when heat can be felt from the top of the boxes. The heat output is better than a HWB, as it is more evenly distributed through the night. Caution must be used however, as overheated, they will probably cause a fiery explosion.



bloody marvellous ! Use mine often for an old ladies comfort

John Hackett


Dear Kris,

I loved your recent article on hot water bottles. It inspired me to buy a ceramic yutanpo and it is incredible. I've been looking at your picture from the article, of the desk surrounded by blankets to trap the heat, and wondered if you'd seen the kotatsu people have in Japan? See this article:

I'm considering one as a maybe slightly more elegant solution than nailing some blankets to my desk :)

Thought you might be interested, apologies if I'm preaching to the converted!

Thanks for reading,

John Hackett

PS, the site is amazing, never stop!

kris de decker



Thanks. The kotatsu is mentioned in the article. But the link you sent had some surprises for me. Most notably: a railway carriage full of kotatsu's !



In an on-grid scenario, a typical western home has a microwave oven which heats quickly and efficiently. For such scenarios, there are termofors made of fabric, filled with cherry seeds.

I have one of these (bought for ~€5) and it keeps warm for about 45-60 minutes after heating it in a microwave for 90 seconds. According to advertising, it works great for cooling too. Haven't tried.

And, of course, it would be easy to make one yourself.

David Veale


We've been using antique footwarmers made from soapstone, and found the thermal inertia to be absolutely amazing -- roughly 2.5cm thick, and 25cm square, they're warmed atop our wood stove and then wrapped in a towel and brought to a cooler room. The significant heat stored lasts for over 4 hours!

Ben Hunkins


Thank you for your article. Our family lives in an off grid cabin in northern New York State. We fill two liter soda bottles (very common in the US) with hot water from the wood stove and then cover them with repurposed sweater sleeves. If we need the heat to be more form fitting then we have small pillow shaped bags (8 inches by 6 inches) filled with rice that we heat directly on the wood stove top. This is achieved by flipping the bag every 5 seconds or so until it's warm enough for the person using it. We also have a few cats :)



les bouillottes sèches
le coussin aux noyaux de cerises
déjà utilisé chez moi, à rechauffer au micro ondes
confort car chaleur douce
souple, donc on peut l'utiliser partout sur le corp
il a une odeur quand il est chaud, ça plait ou pas
si on le laisse trop longtemps chauffer au micro ondes, il brule => danger (c'est déjà arrivé chez moi)
autre système, mais je n'ai pas testé:
le coussin aux graines de lin, ou aux graines de lavande, même principe que les noyaux de cerises


Leonard Hart


The American pop group "Three dog night" was named after the native American practice of using hairless dogs to keep their feet warm the winter. A "two dog night" was a very cold night so the band went one better!

Federico Leva


I agree with the overall idea that we can save a lot of energy by reducing the temperature at which we heat buildings, without sacrificing comfort.

Unfortunately, in my home in Helsinki, I'll never get to need a hot water bottle. Thanks to overzealous central heating which leverages cheap district heating, I've kept the heating off in my apartment for an entire winter and still the temperature never ever went under 18 °C. In the worst case I needed a sweater and extra pair of socks, or I wore a blanket just for extra comfort.

The results of the two mentioned studies were slightly overstated (one is just a model and the other has a pretty small participation) but thank you for finding them. I wish some major building manager conducted a wider experimentation in buildings where people complain about heating temperature. Maybe the old neighbour in the top floor who always demands to turn up the heat can be satisfied by simple solutions such as distributing her some hot water bottles. Then the people at lower floors can get more reasonable temperatures too.

Randall Reade


This is a great idea. Here in Washington, DC, I see restaurants serving people outdoors on the streets during the winter, and they use those awful space heaters. They consume and enormous amount of energy and issue pollutants, and they don't even do a good job. HWB would be far more useful.

I imagine you could write an article on how to keep warm, the old fashioned way. Just a few thoughts:
- Wear lots of layers of clothes
- Drink hot beverages, like green tea (so you don't overcaffeinate yourself)
- Get a dog or cat to snuggle with. Or a partner.
- Take a hot bath and then keep the water in the tub to warm the air, or use the water for a HWB afterwards. Hot baths keep me warm for a very long time.
- Wear a hat. (In many places in the US, men dont' find it "cool" to wear a warm knit hat and would rather freeze). At night, wear a nightcap, like Santa. You lose a lot of heat at the top of your head.
- Keep surfaces warm, or at least not cold. People used to put think tablecloths on tables so that they wouldn't feel cold to the touch.
- Oil lamps help. I find that in a well insulated space, a single oil lamp provides light and quite a bit of heat. Eskimos know that a single candle will heat up an igloo very nicely.
- Keep a room moist. Old timers often put a kettle of water on the coal stove and let it steam the room. A room that is moist holds heat better than a dry room.
- In the evening, sing songs with the family that require you to clap your hands. That will help keep your hands warm.
I'm sure there are 100 other ways to keep warm.



The french foot warmer is an interesting one. One could heat a modern version on an induction stove.

Instead of using water, one could fill it with paraffin to keep it warm for a guesstimate of 6-8 hours. Heat the paraffin to above melting 'point'.

paraffin: density 900 kg/m3, specific heat 2.3 kJ/kgK, heat capacity2070 kJ/m3K, heat conductivity coeffcient 0.25 W/mK, melting trajectory ~50-54°C

Emil Mahnke


Hi Kris,

I'm a physics student at a university in Germany (about to graduate) and I have been reading my way through your blog, for the past year and a half (loving it!).
I'm writing to talk about two things that I think you may find interesting:

Window quilts/blanket:

Windows, even when double or triple-glazed get some of the highest heat losses to the outside. In the night (which is most of the 24 hours in winter), they don't even provide heat input through sunlight. One can increase their insulation value by using curtains, but this is at best a small improvement. However, I have recently found out about these so-called window "quilts" or "blankets", to cover windows with at night. These can be made d.i.y. or there are a number of commercial products available. There are a number of variants of these, but their function is similar: they fit tightly against the window surface, preventing air circulation behind them (unlike curtains), while providing very little in terms of heat conduction through their surface. The performance numbers I've seen online suggests that they can bring a single-glazed window to the performance of a double or triple-glazed window, at a very low price.

Phase change materials:

Reading your article about water bottles, a possible improvement occured to me. Instead of using water, one could use a phase change material (PCM) instead. These store thermal energy as the lattent heat of fusion of the phase change from liquid to solid. Examples of these are the sodium acetate hydrate used in hand warmers, paraffin (wax) or even water/ice for cooling needs. A lot of these materials have energy densities that are seriously competitive (or even exceed) the energy release by a water bottle that is cooling down. They however have one major advantage: since most of the energy is released during the phase change, these materials will release heat at a constant temperature (melting temperature). Water releases lots of energy at first (at less safe temperatures) but the rate decreases exponentially as the temperature decreases (it's literally an exponential decay function). This means that PCMs could provide a significant improvement to water bottles, by releasing energy at a more consistent, safer and more useful temperature.

I've seen PCMs used in thermal batteries, to store energy from electric (or heat pump) heating at times when electricity is cheap. They can also be a very good improvement to a hot water tank, for example for residential solar thermal applications. Another application I've seen is using them as additional thermal mass to buffer out hot days and cold nights.

In the context of the energy crisis that we are fearing for this winter, I actually think that somewhat like you, can help a great deal of people in this situation. I'm trying to get other people to read your articles since you have written many articles about alternatives to the "normal" way of heating ourselves (or rather our buildings). I genuinly think that if some of your ideas spread, it might make a significant dent in our gas consumption (and costs of living!). I'm looking at making myself a window quilt for my appartement this winter, I think it would be great if you could get other people on board doing this!

Kind regards,
Emil Mahnke

Stephanie L Takeshita


For a hand-warmer, I use an extra-wide coffee mug dedicated to this purpose and the microwave, heating for 2 - 2 1/4 minutes (depending on how cold my apartment is); then top it with a small porcelain dish that fits it perfectly, then topping that dish with a single fuzzy earmuff.

The warmth lasts for a good 30-45 minutes when I'm sitting at my PC and reading or watching videos, or doing things that require only some mouse point-and-clicks. No water wasted from emptying out water bottles or waiting for the tap to run hot.

The comments to this entry are closed.