Electricity, heating and cooking

johngalway

This will possibly come more under the "Self Sufficiency" title rather than "Survivalism". Lately, I have been (doing too much reading here ) looking into energy, heating and cooking. Oh, and refrigeration. I think this came from food preservation and living off the grid topics and rather mutated somewhat.

Cooking is a relatively easy one I think, if you had no electricity and no bottled/piped gas. I have been greatly impressed by "Rocket Stoves" and had the utter misfortune of watching some woman cooking (perhaps burning...) some lovely steak on one last night on YouTube.... at 2am The mouth watering sizzle of it all.

There seem to be umpteen ways of boiling water.

I have mainly been looking at wood as the energy source. Though alcohol has cropped up in more than a few links.

Thermal mass stoves for heating the home also impressed me. For a long time I had thought running the stove pipe through various rooms (borderline ridiculous) would be a good idea.

Then I stumbled upon a homemade wood gasifier being used as a fuel source to generate electrickery!

http://www.youmakeenergy.com/alternative-fuels/gasification/gasification-homemade-wood-gas-stratified-downdraft-gasifier-electricity-generator/

Posting these ramblings to see if anyone else has the same interest in this type of technology. It all seems exceedingly efficient, and, frankly, useful!

ATB,

John

krissovo

I certainly am, I was fortunate enough to design and build my own home a couple of years ago. My home is very close to passive and I only just missed out on a passive certificate as I didnt have a porch

I have a 9kw Wodtke wood stove which has a back boiler that feeds a thermal store. I can quite comfortably heat my home using this as its tied into the central heating. Even if I do not have radiators on the heat will be stored for up to 3 days ready to use. I have planted a small wood that I hope to coppice in 2 to 3 years so then I could be free from all home fuel bills.

I also have 8.4 meters of solar panels, works quite well to the point that between April and October I rarely needed to put the water on.

For cooking I am close to finishing a pizza oven outside. Can cook lots more than pizza's . One of my stoves also has a hotplate to cook with. I am going to try and start making my own charcoal so I can BBQ with my own coal.

Electricity is my next obsession I think, I have been playing with homemade wind turbines for a year or so now but would like to take it to a whole new level. Currently I only charge power tools or light my shed with the power, I would like to store this energy with truck batteries for emergencies.

I have a nice stream near me that I may try and use on the sly for a motor. Would be handy to have a deployable generator that I can setup quickly during a power cut.

baords dyslexic

Whats wrong with a good "old fashioned" mulitfuel cooker with back boiler? Runs on wood (+turf or coal if you've got it) does all your cooking, heats the kitchen, heats water is a good place to dry clothes and if you use some "old fashioned" plumbing methods you don't need any electicity for it to work. I've ours set up so I can run it even if the water goes off, the back boiler (only 3kw afaik) is only across the back of the stove so I've cut 3 thick firebricks that can be sat in place in front of the back boiler which cut off the heat.

eth0

baords dyslexic wrote: »

Whats wrong with a good "old fashioned" mulitfuel cooker with back boiler? Runs on wood (+turf or coal if you've got it) does all your cooking, heats the kitchen, heats water is a good place to dry clothes and if you use some "old fashioned" plumbing methods you don't need any electicity for it to work. I've ours set up so I can run it even if the water goes off, the back boiler (only 3kw afaik) is only across the back of the stove so I've cut 3 thick firebricks that can be sat in place in front of the back boiler which cut off the heat.

Nothing at all wrong with it. Although Mr Gormless if he was still around would say you'd be getting too independent for your own good with such a system and would only give you a grant for an electricity using wood pellet boiler instead

What is your preferred 'old fashioned' plumbing method?

bonniebede

love rockets stoves, on my list of things to make or buy.

when my rural retreat gets bought, manana, would love a wood stove and setup like kriss outlined.
sigh....

Ziboo

johngalway wrote: »

.......................I have mainly been looking at wood as the energy source. Though alcohol has cropped up in more than a few links........................

I had considered alcohol stoves due to their simplicity as an emergency backup if other options were not available, but looking around the shops for a source of fuel, the only thing I am seeing is meths, and it is being sold at an extremely high price for small bottles (approx €6 for 500ml). Could anyone suggest either a location where it could be purchased more economically than the DIY shops or an alternative (cheaper) source of alcohol fuel.

baords dyslexic

eth0 wrote: »

What is your preferred 'old fashioned' plumbing method?

Direct back boiler to hot water tank connection, large bore pipe, high hot feed low cold return and no pump. Hot water in back boiler rises and cold water from the bottom of hwt returns to it, equals hot water in tank and no pump. I'm not a plumber but worked it out and fitted myself, neighbor who is a plumber says its fine. Cost under 4k including a new cooker and all the plumbing on what was virtually a new build (but with a 2nd hand cooker could be done for about 1k). The same system would work fine in a log cabin type setup (its in a log cabin type setup) with either a ram pump in a nearby river to supply the water or a higher up spring. Using a larger than usual bore (3/4') for the hot water to the sink you don't even notice that the whole thing is running on less than a 4ft head of water, I had no where to put the header tank higher up.

Learnt a lot putting it in and if doing it again I'd put in a much bigger hwt and have one with 2 coils on top of the direct connection so I could add some sort of solar heating later. I would also put in a much bigger header tank maybe 200l or more. The Chimney is far from perfect but works and I'd certainly do it differently, I'd change it but that would be far to much work at this stage, but again it proves that if you get some of the basics right you don't need a massive high chimney to get a good up draught, top of Chimney is only about 15ft above ground level.

fodda

http://www.grow-your-own.ie/energy.html

http://www.grow-your-own.ie/energyefficiency.html

http://www.grow-your-own.ie/woodboilers.html

http://www.grow-your-own.ie/woodburning.html

http://www.grow-your-own.ie/insulation.html

Various related topics.

eth0

baords dyslexic wrote: »

Direct back boiler to hot water tank connection, large bore pipe, high hot feed low cold return and no pump. Hot water in back boiler rises and cold water from the bottom of hwt returns to it, equals hot water in tank and no pump. I'm not a plumber but worked it out and fitted myself, neighbor who is a plumber says its fine. Cost under 4k including a new cooker and all the plumbing on what was virtually a new build (but with a 2nd hand cooker could be done for about 1k). The same system would work fine in a log cabin type setup (its in a log cabin type setup) with either a ram pump in a nearby river to supply the water or a higher up spring. Using a larger than usual bore (3/4') for the hot water to the sink you don't even notice that the whole thing is running on less than a 4ft head of water, I had no where to put the header tank higher up.

Learnt a lot putting it in and if doing it again I'd put in a much bigger hwt and have one with 2 coils on top of the direct connection so I could add some sort of solar heating later. I would also put in a much bigger header tank maybe 200l or more. The Chimney is far from perfect but works and I'd certainly do it differently, I'd change it but that would be far to much work at this stage, but again it proves that if you get some of the basics right you don't need a massive high chimney to get a good up draught, top of Chimney is only about 15ft above ground level.

interesting. my neighbour has this kind of setup for a hot water cylinder and upstairs radiators. there is a pump then for the rads downstairs. would the water heat up any faster if you added a pump?

baords dyslexic

eth0 wrote: »

interesting. my neighbour has this kind of setup for a hot water cylinder and upstairs radiators. there is a pump then for the rads downstairs. would the water heat up any faster if you added a pump?

It really is the old way of doing it, a pump might not work as the flow may be too fast for a directly coupled system and you might end up stiring up the layers of hot and cold water in the hot water tank. It is a bit slow to heat the water say 4hours for enough for a bath but once its going every day there's always enough in the tank for a couple of baths.

You can have the hot water tank quite away from the back boiler but then you have to have the return pipe (for the colder water back to the back bolier) low down often burried in the floor and the hot flow pipe to the tank high up so you develop the maximum flow with the hot water rising and the cold water flowing back. I have the hwt very near and just above the hieght of the bolier so just having the flow and return pipes one above the other works fine (using one inch copper).

Its not a system I like to hang rads off because it does what it does well without being over complicated. Under the worst possible conditions with no power we have one room thats well heated, we have hot water and can cook, and by cook I don't mean heat a tin of beans, it will do a full roast without a bother but yorkshire puddings need a bit of special effort to get the oven extra hot and to keep the temperature up.

If we had an upstairs and an upstairs bathroom then a towel rail type rad in the bathroom would be a good idea as it could run off a thermostatic valve and use any excess heat that can otherwise make the hot water a little to hot.

If you are thinking of doing something similar and want any technical info let me know.

johngalway

It's something I'm just trying to tease out for the future, or as Bonniebede rightly put it Mañana. I'm not doing down or trying to big up any system over another, what will win the race, IMO, is smart simple efficiency using simple easily understood and easily fixed technology, something that'll work excellently regardless of whether the rest of the world is going to sh1t, or not.

I am also thinking of going down the route of having a wood to coppice, like Krissovo who I'm not at all jealous of right now - where I'll get the land from for the wood is another matter as the farm is currently all spoken for. I'm currently on a planting spree, but I can't coppice, just put in wind breaks and the odd small cluster here and there.

Electricity is something that particularly, well, annoys me! I have to be realistic with a non existent budget But there are just so many mod cons that people are addicted to, most can be discarded but some are genuinely useful, whether that's a power tool, a kitchen or laundry appliance, or even a computer - note to self sort of some way of turning the bazillion PDF's into hard copy.

The guy who runs survival blog seems to plump for solar. But living in Connemara I think I've seen the sun four times since April So back to efficiency... Wind power? We get a ton of wind, but is that technology when you compare it's output to it's cost really worth it? I'm not convinced. Water power, I have only drains unfortunately, but some small micro scale water generator may be worth exploring. Unlike other years those drains have not once dried this year.

I am still interested in the power generation via wood burning idea. If there was a way to incorporate all the things wood can do, heat, cooking, hot water, and power, into one contraption... There were even cars run on wood power in Europe post WW2!

Cob (?) stoves are another thing of interest, warm yer backside while ya take the weight off yer feet

A lot more reading, poking, and researching to be done by me!

baords dyslexic

@johngalway > re electricity have you taken the first step and worked out exactly how much you need?

Assuming power goes off tomorrow and you could generate your own by whatever means then you really need to know what the minimum amount of electricity you can get by with and what you can do with out.

We can get by with nothing zero nada, but then that wouldn't be very convienient and days would be a bit short but if you can cook, keep warm and have a bath without using electicity then what essentials are there that really need it?

Khannie

Did a bit of reading today on making your own wind turbine. It actually looks like a fairly straightforward (if time consuming) job. Some reading, magnets, copper wire coils, fins, bearings, something to stand it up with. Coastal areas average 6m/s wind speed in Ireland which is decent. Initial reading suggests that a 500 euro investment and a bunch of your time (probably 1-2 weeks) you could have a 1KW turbine. Battery bank (for increased reliability) would obviously set you back more cash and effort. Seriously considering this as a half fun and learning, half investment type project but I wont get to it 'til next year.

If you just wanted enough to cover an A rated fridge and some CFL lights and maybe saving your washing for windy days you could get away with less investment.

prints

Hi all,


In Ireland, one of the best ways to sort heating and cooking is with a stove that has a hot plate on top. This gives efficient heat and a method for boiling and frying. A good start that's relatively easy to set up in any home. For a little over E400 you can get 1 1/2 tons of coal/smokeless fuel and you have a supply of fuel that will see you through a full year.

That coal can be bought in bags (38 x 40kg bags)and stored easily if you have a garden or shed. The great advantage with coal is that you can get it right away and it keeps well.

If you have the money an esse ironheart(cooker stove) is a great investment. This stove/cooker allows baking, frying and boiling. It also provides hot water and will heat a couple of upstairs radiators too.

These stoves work on the thermosyphon principle which means that the pipes have to have a continuous rise from leaving the stove to the destination (rads, tank etc).
A bit of careful plumbing sorts it well and then no pump is needed- the heat of the water causes it to circulate.
I burn 1 bucket of smokeless coal in mine each evening and it heats my living area downstairs and two rooms upstairs and it provides all my hot water (including shower). It's also great for drying a clothes horse full of clothes at night if left on front of it.

As regards electricity, a generator provides good occaisional/emergency use. Some deep cycle batteries with a solar panel to charge them and an inverter will power a lot of the less power hungry conveniences too and can be used to charge batteries for torches, laptops etc..

I've read that a car radiator fan attached to the alternator (and placed in the wind) can be used as a sort of wind turbine to charge a battery bank in an emergengy - not sure if it would work though.

Hope this helps

BTW Miles Stairs has an interesting and informative site at endtimesreport.com.
Some of it is useful in an Irish context.
He lists the priorities for preparedness/survival under useful headings aswell. He hasn't updated it lately but it's still mostly relevant

krissovo

I've read that a car radiator fan attached to the alternator (and placed in the wind) can be used as a sort of wind turbine to charge a battery bank in an emergengy - not sure if it would work though.

My homemade wind turbine has a car alternator and I use 4ft lengths of waste pipe that I have cut for the blades. Its nice and light and very cheap and does not stress the bearings on the alternator too much. The blades do break now and again but they cost next to nothing.

prints

@Krissovo
Any chance of more details about your alternator/turbine please. Do you have 12v batteries, inverter,etc? Any pics?

krissovo

My setup is so simple at the moment, its a basic car setup as I only use the output to charge car batteries as I am a classic car fan. In a power cut I simply use a 1000W inverter and a few car/van batteries and plug in my home heating and one lighting circuit

My inspiration was this this website: http://www.mdpub.com/Wind_Turbine/

I dont have pictures to hand but next time I set it up I will snap some and put up a circuit diagram. I got all parts at local scrappy and B&Q, I think it cost about €80 as I had a spare alternator.

bonniebede

johngalway wrote: »

I am also thinking of going down the route of having a wood to coppice, like Krissovo who I'm not at all jealous of right now - where I'll get the land from for the wood is another matter as the farm is currently all spoken for. I'm currently on a planting spree, but I can't coppice, just put in wind breaks and the odd small cluster here and there.

!

Plant some food trees as well, hazel and sweet chestnut do well in ireland and you can make great alternative typs of flour with them , without all the effort to grow grain, and anyway wheat doesn't do well here.
You can eat them, coppice them for forewood as well.

colonel-yum-yum

I know different types of stoves have been covered before, but didn't notice this exact setup before.
http://lifehacker.com/5861130/build-a-camping-rocket-stove-from-leftover-food-cans

No6

I was in a cob built house in co sligo last year and they had two natural fridges which are basicly a chamber in the wall on the north face with air vents to the outside and a heavy insulated door and seal to the inside. It keeps things cool for most of the year, according to the owners it struggles a bit on the hottest days of the year but is fine the rest of the time!!!

baords dyslexic

No6 wrote: »

I was in a cob built house in co sligo last year and they had two natural fridges which are basicly a chamber in the wall on the north face with air vents to the outside and a heavy insulated door and seal to the inside. It keeps things cool for most of the year, according to the owners it struggles a bit on the hottest days of the year but is fine the rest of the time!!!

If I was ever building my own house that would be a feature I'd inculde. My bother in law a farmer in the UK has an old farmhouse with a "pantry" which is probably not as cold as the natural fridges but being built on the north side of a house and into the hillside is an excellent store room for all sorts of perishable items. The main point of it other than the coolness is that the temperature and humidity hardly changes during the year. I suspect one of its orignal uses was for hanging game as the ceiling is full of very heavy hooks.

krissovo

colonel-yum-yum wrote: »

I know different types of stoves have been covered before, but didn't notice this exact setup before.
http://lifehacker.com/5861130/build-a-camping-rocket-stove-from-leftover-food-cans

Thats a nice small set up, would make a great summer stove and you can use it camping. It would be intersting to see how it would work indoors.

Grizzly 45

http://deadwoodstove.com/
TBH,if anyone was handy with a welder and had some metal lying around,you could weld one of these up in a couple of hours.Think even large round metal pipe or a T Flange connector could be improvised into one of these.Scrounge and adapt first.Buy if necessary as a last resort.;).

Khannie

Grizzly 45 wrote: »

http://deadwoodstove.com/

Looks very similar to a rocket stove.

colonel-yum-yum

Here's an interesting one I haven't seen before.
Biolite Stove

Open wood fires are inefficient, wasting potential energy and creating toxic smoke due to incomplete combustion. Carefully designed stoves that use fans to blow air into the fire can dramatically improve combustion. However, such stoves require small amounts of electricity to power their fans and most people who cook on wood are without grid or battery access. BioLite stoves solve this problem by converting a fraction of the fire’s thermal energy into electricity to power our combustion improvement system. Excess electricity is made available to users for charging small electronic devices such as mobile phones, LED lights, GPS and many others.

There's a home stove


And a camping stove

Khannie

Brilliant piece of kit. I wonder how much juice you could theoretically make with that thermoelectric device. Very impressive.

colonel-yum-yum

Khannie wrote: »

Brilliant piece of kit. I wonder how much juice you could theoretically make with that thermoelectric device. Very impressive.

As even the larger home stove is only outputting to USB, I would assume very little, but I definitely think there is room for upscaling the idea. Many people have wood burning stoves now and some form of addon to generate power from lost heat would be a great idea.
Erm.... I mean TERRIBLE idea!

*runs to the patent office*

colonel-yum-yum

colonel-yum-yum wrote: »

*runs to the patent office*

Ah dammit!
http://www.siberianstoves.com/Normal-PG.html

Khannie

50W. That's pretty decent.

sfakiaman

I remember, back in my youth, selling fridges made of plaster with a hollow in the top which you filled with water. The evaporation of the water kept the interior cool. When I lived out bush we had water in canvas bags that stayed cool by the same principle.

eth0

Nice yoke but wonder would it be more efficient using a stirling engine?
You can buy those thermoelectric modules on ebay fairly cheap and stick them onto any ould heat source but you need a cold source as well or at least a fan to keep the other side cool.

CamperMan

we did try to live completely off grid a while back..

we had a small plot of land up in Leitrim with a mobile home on it, we collected rain water, had the large bank of batteries rigged up to solar panels, a backup generator just in case... gas cooker, diesel heater, gas heater...

the whole setup worked a treat, but after 9 weeks, we left.. the neighbors were very noisy.. so bloody inconsiderate

Grizzly 45

Yeah,yeah,can the laughter!

http://blog.modernmechanix.com/2007/11/14/icyball-is-practical-refrigerator-for-farm-or-camp-use/

and there is a link there on how to build one or two in the article.

colonel-yum-yum

A slight variation of the pocket stove idea, that should be easy enough to run up with the right tools.
http://www.180tack.com/180stove.htm

touts

Time to catch up on this thread. Looks like the government are going to majorly P*** off the Taliban of the public service unions later today. I predict strikes and blackouts by the Summer.

http://www.rte.ie/news/2012/0222/state_assets.html

Khannie

colonel-yum-yum wrote: »

A slight variation of the pocket stove idea, that should be easy enough to run up with the right tools.
http://www.180tack.com/180stove.htm

I got a 404 on that.

baords dyslexic

Khannie wrote: »

I got a 404 on that.

If you go to the home page you get:





180tack.com is undergoing maintenance

colonel-yum-yum

Hmm, must have gone down since yesterday. The site needed an update in fairness, bugs all over the place!

Pat Mustard

Ziboo wrote: »

I had considered alcohol stoves due to their simplicity as an emergency backup if other options were not available, but looking around the shops for a source of fuel, the only thing I am seeing is meths, and it is being sold at an extremely high price for small bottles (approx €6 for 500ml). Could anyone suggest either a location where it could be purchased more economically than the DIY shops or an alternative (cheaper) source of alcohol fuel.

Not an alternative to DIY shops, but Woodies sell 2.5 litre cans of meths for about €18, if memory serves.

eth0

The Mustard wrote: »

Not an alternative to DIY shops, but Woodies sell 2.5 litre cans of meths for about €18, if memory serves.

Jaysus thats a lot. I remember buying E85 for 90c a litre a few years ago, dunno why methylated spirit costs so much, never actually thought it could be expensive cause the e85 was so cheap

Methanol costs a lot but the percentage is very low these days i think

cruizer101

I think one of the main essentials we run off electricity is the fridge and maybe lights. Light can be got from other sources such as lamps and that but refridgeration is a tricky one.

My mum told me how when they used to go camping the got a basin of water in which they sat the milk over which was layed a wet tea towel, once left in a shaded area the evaporation would keep the milk cool. There has been mention of this elsewhere in the thread how evaporation can be used to cool.

In fact thats basically how modern fridges work, they evaporate a refridgerant inside which is then pumped to the back where it loses the heat it absorbed. So the electricity is just driving a pump.

So why not drive the pump in some other way, personally I don't see why some sort of hand operated pump could be used along with a well insulated fridge but thankfully there is another way.

Anyone who has a caravan might be familiar with the fact the fridge can run of electricty or gas. The first time I heard this I couldn't believe it, how could burning gas (creating heat) cause something to cool, was there a mini gas turbine behind the fridge driving a motor, seems a bit complicated.

So I googled, and here was the result.

Heat can be used to drive the refridgerant around the cycle and in fact ingeniusly involves no moving parts (ideal for a SHTF situation as moving parts mean wear and that means repairs, whcih aren't ideal). There is no point in me explaining how it works its explained well in the link, with nice animation and all.

They are designed to run of gas but I'm sure another heat source could eb used easily enough.

These fridges are expensive enough to buy, it may in fact be cheapest to pick one up by buying a whole caravan that has a working one. Some nice bits of electrics in caravans too, inverters and that.

I'm after rambling a bit more than meant to, but thought would be of some interest to some here anyway.

Red Neck Hughie

Ziboo wrote: »

I had considered alcohol stoves due to their simplicity as an emergency backup if other options were not available, but looking around the shops for a source of fuel, the only thing I am seeing is meths, and it is being sold at an extremely high price for small bottles (approx €6 for 500ml). Could anyone suggest either a location where it could be purchased more economically than the DIY shops or an alternative (cheaper) source of alcohol fuel.

Cheaper Alcohol.. throw some potato skins or basically anything with carbs into a plastic bag with water and tie it off, some time later you get alcohol. The more sugary stuff you put in the more alcohol you get out.

Easy electricity.. 1 take a cheap battery drill, remove the battery
2 wrap some paracord around the chuck (many times)
3 connect a torch light between the terminals where the
battery terminals would have been (you might need a
little wire or even a paperclip if youre stuck
4 pull the cord hard and the bulb will light
When you do this once you'll see how important wind/water/bicycle electricity might be post shtf

The basic motor has no semiconductor ****e thats vulnerable to emp either..

Mightymouse vs Dangermouse

Hey Guys, just checking if you ye have or know anyone who has built log/wood cabins to ilive in say 25 by 20 foot???
Is there ways around the planning permission side etc???

Doc Ruby

Mightymouse vs Dangermouse wrote: »

Hey Guys, just checking if you ye have or know anyone who has built log/wood cabins to ilive in say 25 by 20 foot???
Is there ways around the planning permission side etc???

I don't think you need planning if its a temporary structure like a portacabin, so maybe just don't dig foundations and tie it down or something?

Tabnabs

Mightymouse vs Dangermouse wrote: »

Hey Guys, just checking if you ye have or know anyone who has built log/wood cabins to ilive in say 25 by 20 foot???
Is there ways around the planning permission side etc???

Be worth asking in the Actually you did...

http://www.boards.ie/vbulletin/showthread.php?t=2056597817

eth0

Do they still make these? Great yokes, fit onto a regular 11.34kg butane cylinder and no messing around with tubes or separate regulators.

baords dyslexic

Have one myself aquired when someone was clearing out there garage and was looking to post something about them but when I couldn't find a pic on google let alone anyone selling them anywhere I decided not to.

baords dyslexic

Forgot to agree with eth0 they are "Great Yokes" :cool:.

We have plenty of other gas stoves, home kitchen, in caravan and in one of the sheds so I don't use it much but have used it for checking if there's anything left in a gas bottle. Sometimes a bottle thats empty as far as the caravan stove is concerned will still have enough gas to run the single burner for quite a while (at least enough for a brew) so might be useful SHTF for getting the last bit of use out of otherwise empty bottles, before you get the hacksaw out and turn them into a woodburning stove.

eth0

baords dyslexic wrote: »

Forgot to agree with eth0 they are "Great Yokes" :cool:.

We have plenty of other gas stoves, home kitchen, in caravan and in one of the sheds so I don't use it much but have used it for checking if there's anything left in a gas bottle.

I always use a match for that. Not a lighting one of course, used to be mad for doing this when i was a wee lad cause I liked the smell of the gas until i was caught and told it wasn't too healthy.


another thing we used have was a very small gas cylinder - about 1kg or less with the same connector as the big ones and some sort of adaptor that you could fill the small cylinder from the big one. No idea where they are gone though, probably got rid of

Mightymouse vs Dangermouse

yes tabnabs i did, tryn to get info off as many people as possible or find someone in a similiar position.

bonniebede

Maybe this is not news, it has only caught my eye. It's a polystyrene bead filled bag which acts like a slowcooker once heated food is placed in it.

http://nb-wonderbag.com/content/what-wonderbag

It reminds me that my Dad used to talk about cookng stews in a barrel of sawdust during the emergency, same principle. I'm a slow cooker fan, so it caught my eye.

You have to bring it to the boil first, but I'm thinking a rocket stove could do that with a handful of twigs, then pop it into the wonderbag and hey presto, a whole pot of food cooked for little fuel.

Then i was thinking how much could it cost to make?

And lo and behold someone was there before me.

http://thermalcooker.wordpress.com/category/wonder-box/

You could buy bean bag filler,

http://www.beanbagshop.ie/index.php?option=com_virtuemart&page=shop.product_details&flypage=vmj_naru.tpl&product_id=4&Itemid=1

but the suggestion above is to make your own free by grating solid polystyrene from packing. We used to spend ours doing this as kids, we called it artificial snow. If you don't have packing to hand, I pick it up free at our local electrical retailer, where it is dumped in a big skip with other waste products. (I use it in patio planters instead of gravel for lightness). Now all I need is a bribable 6 year old, hmm.

also nice instructions for making it here.

http://www.iwillprepare.com/cooking_files/Wonder_Box.htm