efficient heating/cooking/stove design.

**Ren** · 07-30-2012, 08:48 PM

Just incase others are interested in this area I thought I would provide a link to a site I have found very useful lately.

I have, as a side project, been developing a multipurpose wood combustion unit, for use in survival/camping and/or off grid lifestyles. Part of the fun has been learning to weld and shape metal, but the goal is the design of a fireplace that uses less fuel, distributes more heat into the immediate vicinity (instead of straight up the flue), allows for frying/baking/boiling of food/water with the extra benefit of thermoelectric generation of electrical energy.

This will probably be the lone post in this topic, but hey, maybe someone else will find it useful. Maybe the Northern hemisphere lads moreso than us Aussies, though it still gets pretty cold down here from time to time.

The website I have found invaluable is here:

Stove Design - Stove Design

All the info is free, and very useful in understanding the principles.

Might post some pics of some of my builds if anyone is interested.

Regards

**David Savage** · 07-31-2012, 08:01 AM

Sounds very interesting Ren. I'd love to see some of your builds.

**Ren** · 07-31-2012, 04:56 PM

No worries David. Thanks for the interest.

Here is the first model. Most of these designs are built from abandoned lpg/bbq gas bottles, completely drained first of course! I went to the local scrapper and he practically begged me to take them off his hands. I think there must be a fee associated in their disposal, because every other scrap piece of metal on his yard was strictly "out of bounds". On this model I wanted to build a compact but versatile unit that could be taken camping. Legs are fully adjustable for a level cooking surface on almost any terrain. The top of the stove is open, so you can load from the front or top if the wood is too big to fit through the door. (This is actually a really good feature, as a large log can stand vertically, instead of smothering the flames. Fire always burns better uphill!) The cast iron pan you can see below fits snugly on the top, once the lid is removed and allows for maximum heat transfer from the fire to the pan. Being removable allows for easy cleaning/serving/cooling, and is safer in the event of a fat or oil fire in the pan.

There is a computer fan at the front to encourage airflow. On later models I have upgraded to a smaller DC blower which is much more focused in its output for 1/2 the electrical input of the bigger pc fan. It is also mounted under neath now, out of the way, and is directed in a way as to focus a stream of pre heated air directly on the coal bed. This works a charm, I can start the fire with a piece of charcoal, a piece of newspaper, and a log. no kindling necessary. Just light the paper, place charcoal on paper, and turn on fan. Once charcoal is glowing its all down hill from there. Blow enough hot air on the glowing coal and you can get even the biggest chunks of wood alight from it. Damp wood isnt a problem, and you can let the fire burn right down, load it up with fuel and switch the fan on and in a couple of minutes its roaring again. I left the fan on for about 25 min in one of my tests only to come back to it and find the whole backside of the cylinder glowing red! So you cant just leave it on blast furnace style. It certainly puts out the heat though. The end goal with this "forced induction" is to use a TEG to provide power from a heat differential to power the brushless blower, which inturn will have its circuit hacked and run SG style so the excess can be funneled to another load/battery. This way, once the stove is hot, the TEG becomes my primary source, the fan my energizer and I get work done and electrical output as long as the stove stays hot. The TEG part is proving to be a little tricky, however I feel the concept will work fine once that is sorted.15 watts aint much at home but out in the bush, the ability to convert wood into heat AND a small amount of power would be awesome.

Copper pipe around circumference is an attempt at hot water on demand, needs some tweaking though. Chimney and legs all pack down and fit inside the stove for transport. There are a number of other features but Im typing one handed due to injury and cant be bothered getting into them at the moment.

These next two pictures are designs I drew up for a friend to get manufactured for his house. He lives off grid in the mountains and wood fire is his only method of heating his living space. He had a problem with his $2000 fireplace in that it would starve with the door closed, hard to light and only heated the room it was in, and that poorly. Just poor design really. Well, we sure fixed that. A fan and appropriate ducting I built and hid in the bottom gives him blast furnace status at the switch of a button for less than 4 watts (important for him being off grid). The rest of the chimney/flue designs we had fabricated professionally from stainless (not the ideal material, but long lasting and pretty) and now it heats up his house really well. The three channels through the base of the chimney are heated by exhaust gasses and three brushless fans force air through them into the room. The chimney then passes through a wall into the lounge room to a large heat exchange before exiting outside. End result is more heat in the room, less out the chimney.

And here is another one Im still working on, this one has plans to have an oven inline with the flue, so you can cook on the hotplate and bake/grill in the oven at the same time, or alternatively, just leave the oven door open to heat the room (heat exchange). Having a stab at a nice glass front on this one too.

All work is based on the pdfs I linked above, basically boils down to efficiencies. Less fuel, better heat transfer, less emissions (cleaner, hotter combustion) etc.

Hope u got through to the end without falling asleep!

Regards

**Ren** · 07-31-2012, 07:13 PM

just found an old video of my "hiking edition" built from a 4kg bottle. You can hear and see when the dc blower is turned on. Once this thing gets up to temp exhaust fumes are literally non existent, all you see is a slight shimmering of the heat escaping. Part of the reason is that the flame is drawn up the chimney and all the smoke has to pass through this. I had it roaring the other day so hard there was a flame coming out of the top of the chimney, thats about 5 feet high.

https://www.youtube.com/watch?v=dravFY-eOtw

**Tom C** · 11-02-2012, 08:51 AM

Originally Posted by Ren

just found an old video of my "hiking edition" built from a 4kg bottle. You can hear and see when the dc blower is turned on. Once this thing gets up to temp exhaust fumes are literally non existent, all you see is a slight shimmering of the heat escaping. Part of the reason is that the flame is drawn up the chimney and all the smoke has to pass through this. I had it roaring the other day so hard there was a flame coming out of the top of the chimney, thats about 5 feet high.

https://www.youtube.com/watch?v=dravFY-eOtw

put coal or coke in there and you have yourself a forge!! nice build, I like the rocket mass heaters for efficient wood heat.

Tom C