Portable Rocket Stove About $25

Intro: Portable Rocket Stove About $25

I camp. I forget my propane. I like my coffee. So I need a wood burning system that can boil water. I saw the concept of a rocket stove deployed using cinder blocks, but the idea of packing 70lbs of cement bricks seemed a bit over the top, So here is a rocket stove implemented using 2lbs of stuff: metal duct work, some scrap metal pieces and such. The whole thing fits in a milk crate and you can get a super hot fire going in about 10 minutes

STEP 1: The BOM.

So I had a lot of material laying around and didn't have to buy it, so my build replaces some of the items with scrap I had laying around but I'll list what I would of bought to use for the stuff I didn't have to buy. What you need is

1) 6" diameter duct work 90° elbow

2) 6" right angle converter to 10"x6" rectangle duct boot

3) 60" duct cleat

4) a bunch of #8 nuts and bolts,

5) 2 8" runs of angle iron/ slotted angle (I had some left over aluminum angle iron)

6) plate steel thicker (13 gauge? I had some sheet steel)

7) expanded steel, 12"x36" total,

Again, improvise. I made a burn chamber from a piece of metal that was a computer fan cover instead of folding some expanded steel into an open box, use what you have from the leftover bin.

STEP 2: The Basic Frame

the assemble of the basic frame is 10 minutes. attach the elbow to the boot such that the joints of the elbow give you a good range of motion. drill out from top and bottom two holes so that you can attach the two parts together at the overlapping metal. Then cut up the connector piece to make lips for the rectangular box and slide them over edges to give the rectangular opening some rigidity. Use nuts and bolts to attach the legs to the outside corners of the box. I left the bolts kinda long, like 1" bolts, so that I could use the the bolts as resting and anchor points for the internal components, but that is up to you.

When you've done this you have the frame not only is the rocket stove, but it conveniently has only 3 points of contact with the ground, that really shouldn't get too hot so you should be able to put it on the table. Also the rotating nature of the elbow allows you to level the cooking surface to whatever you need.

STEP 3: Internal Details

As the duct work steel is not really made for contact with fire, I wasn't sure how well it would take the burning wood, so I made a burn tray and basket out of much thicker metal I had laying around. The bottom plate is just a layer to catch falling ash, and the top is a basket with lots of air flow through the bottom. I had a metal basket (the black one) that I used, had I not had that I would of folded up a basket from the expanded steel. this basket I want mostly level and as the boot is slanted I installed two longer #8 bolts on one side to put a tilt on the basket to level it. I also added a third bolt to attach it to the burn plate.

For the burn plate I first made one out of cardboard to get the fit right, and then copied the cardboard template onto the steel to cut it out .

STEP 4: More Inner Workings.

the feed for wood and air is from the 6" elbow. I cut about a 5" width strip of expanded steel for the wood feed. as a result the bottom of the 6" diameter elbow will always be a clear path for the air flow. I have the 5" strip resting on the basket. All the parts can easily come out none of them are screwed in. Note how the screws of the legs stick out and pin down the burn chamber assembly.

STEP 5: Grill Top

I thought this is a clever solution to securing the grill top. I made the grill top from a cut section of the expanded steel making sure I had triangles on the edges. I folded down 4 corners of the triangles just so that they would pinch the top of the duct boot. In this way the grill top is reasonably secured to the rocket stove.

STEP 6: Make a Fire

some newspaper, wood pellets, twigs, and sticks. the newspaper and twigs caught almost instantly with a match. The wood pellets took some time. at that point you feed the bigger pieces through the elbow into the burn area. Note also I took a burning leaf to the edge of the elbow and you can see the airflow in the smoke.

STEP 7: Some More Pics. and a Note About Galvanized Steel

tada!!!!

Now there is a lot of warnings about using galvanized steel in stoves. Galvanizing is a process where the metal is infused with zinc, and when heated very hot, emits fumes that are dangerous. For my project I specifically used non-galvanized duct work, but my burn plates are galvanized metal. The thing is, the exact danger of the zinc fumes is debatable, and so is the temperature that creates the fumes. The big thing though is almost all the warnings about zinc fumes are based on indoor or poorly ventilated areas.

This stove is specifically for outdoor use, aka the very best ventilation. Also it is clear that after hot and several burns, the zinc is burned off. My advice is test fire your stove several times and get it nice and hot before using it for cooking or sitting around, and if it needs to be said, don't use indoors. Here is a quote from a discussion I read about this issue:

"I read a recent post which mentioned galvanized pipe and toxicity and realized this is a persistent myth in stove circles. I have a background as a chemist, my work includes machining and fabricating, and I think I know enough about galvanized to ease some fears and help dispel the myth.First, galvanized does not give off 'cyanide fumes'. It DOES give off zinc oxide fumes, which can cause metal fume fever. Metal fume fever is an immune-response condition that goes away in a day or two as your body absorbs the zinc. It's rotten, much like the flu, but it is rarely fatal, usually only when the exposure is extreme and the person has a pre-existing lung condition. It happens to welders all the time, almost considered to be a standard occupational hazard. Welders who work in a enclosed environment and don't wear protection develop resistance rapidly.Second, galvanized steel rarely gets hot enough to create said fumes except under conditions of welding, grinding or casting. During a stove test, I managed to oxidize 4' of my galvanized flue (it was under a fume hood, just in case). White oxides formed on the pipe but none was released into the air as fume. The fume is extremely visible when welding on galvanized material, as thick white smoke.Zinc boils at 907C, ZnO at 2360C, and rapid oxidation occurs at much lower temperatures near the melting point of zinc (420C). Once the zinc has been converted to oxide, it is safe. Your stove will never reach 2360C without forced air or oxy mix. I personally use a fully oxidized white zinc-coated elbow as part of a stove I operate indoors, and it is completely inert. I have never experienced metal fume fever myself as I always am sure to have good ventilation and a respirator if I weld galvanized material.I think galvanized is actually a better material for heat risers if you wish to use thin steel. The layer of zinc oxide will help protect the steel from oxygen and heat damage, I always use galvanized for heat risers in my small stoves and it seems to hold up very well. I always fire them gently at first to oxidize the zinc rather than melt it into a pool at the bottom of the riser. Any oxide fumes will find their way out the flue and not into anyone's lungs.Finally, galvanized steel is commonly used, within code, as an exhaust duct for gas appliances (go look at your hot water tank or furnace) and even to BUILD WOOD STOVES! Ex. www.rileystove.com/products/stoves/riley/flap-jack.html is constructed with 18ga galvanized steel! No Riley customers have died yet!"

STEP 8: Cooking Test

complete success! made a 2 foot full fire from just some twigs, leaves, and pine needles and one match. Really burned the metal looking for the tell-tale white smoke of zinc, nothing. Time too cook up dinner. The full enviro-brick compressed sawdust wouldn't quite fit; I could of forced it but I felt that would smother the fire, so I cut it into 4 parts and decided to try cooking on just 2 parts, aka, 1/2 a brick.

Comments

[cuyler1]

I love this site and wish to ask Instructables to retract this creation . Should the EPA get "wind " of this further ramifications could occur. To the author of this ible blue stove pipe might be an alternative. Zinc fumes are highly toxic!

[jleslie48]

I never specified any pipe to be used other than the size and shape. The pipe I used has been specifically picked out to not have any Zinc galvanizing. With that said, taking precautions against ANY coatings on metal is good practice. With respect to zinc fumes, from all literature it is clear that Zinc fumes are dangerous in high concentrations in closed areas/poor ventilation. Given the outdoor nature (read: open areas, very best ventilation,) and incredibly little amount of material invloved, (read: minimal capability to create zinc fumes,) and the efforts to remove the zinc that can easily be applied, (read comments, and online,) one can decide the risks of the zinc fumes for themselves.

[jleslie48]

the real thing that inspired this build was also the firepit at the last camp site we were at was 100 feet away and on the wrong side of our camper. we wanted a fire closer to the center of where we camp. This little stove fits the bill.

[Taz-Hood]

Thank you very much for this enjoyable and clever Instructable! I have to ask a trio of stupid questions, so please forgive me. What is a "rocket stove"? Would it be improved with the addition of a small, battery powered fan? Could this be scaled down for a stove to take backpacking? Thank you!

[jleslie48]

1) a rocket stove is a stove design that creates a airflow by evacuating air and having input air sucked in.

2) fan would definitely improve it, just like any bellows.

3) LOL, I was up half the night designing a backpack version. The trick for a BP version is that it should fold flat. very do-able.

[kkreitman]

Just curious....I thought a rocket stove required a vertical chimney 3-4 times longer than the horizontal burn chamber to properly create the draw to gasify the fuel. Does this stove do that?

[jleslie48]

I haven't tried putting a flue on it to see if it works better, but I know as it is is shown in this instructable, it works really well. I also noted that when I burnt enviro-bricks,( a standardized size and weight bio-matter,) they burn 3x faster than on an open pit fire, aka they are buring 3x as hot and fast. I also noticed that charcoal brickets burn 2x as fast; again, they are buring a lot hotter (aka, faster)

[marvinwbarr]

To be a proper rocket stove the combustion chamber must be three times taller than its diameter, and preferably insulated.

[jleslie48]

probably, but this design works quite well as is.

[Angstridden.Hipster]

Hi, regarding getting rid of the galvanized coating. A MUCH safer way to handle this is to let the parts soak in vinegar rather than burning. Several of my local stores carry Gallon jugs of Vinegar and you can strip the Zinc coating safely and easily with this. Just make sure that

1. you do this with excellent ventilation

2. there are NO open flames anywhere nearby

3. you rinse the parts well

4. pour baking soda into the waste Vinegar until it stops fizzing and then dispose of it.

So what happens is that the vinegar (an acid) bonds with the zinc metal and ejects hydrogen gas and some vinegar fumes. what is left in the wash is zinc salts (the same kind used in cough lozenges) and the vinegar can be neutralized with some baking soda.

[jleslie48]

excellent advice. to clarify, the very best, absolutely safest ventilation is OUTDOORS. Also these duct sections I used are available without galvanizing in the first place, but following this advice, and then doing several burns, will remove any coatings/oils that are on the metals.

[jleslie48]

cooking test, fire started with just some leaves, twigs and pine needles. good flame, threw on a half a sawdust brick.

[the dan of many trades]

http://www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo This is an article on how galvanized and zinc coated metals are deadly and how one blacksmith died from it. Awesome design, just be careful.

[jleslie48]

yes I read that article too. he was cooking many galvanized pipes, indoors, in an oven, generating, "flares off white zinc oxide smoke and leaves heavy soot like yellow and white oxide deposits...his was not a small amount of zinc smoke. It was thick enough in his well ventilated shop that..." This is a level of zinc oxide of about 10,000x what my 2 little pipes would do. I would still NOT use my stove indoors no matter what. same goes for propane, stoves, or just about any camping gear.

[The Sam D]

As an alternative, you could use like 4 - 6 inch ducting and bring your leaf blower. I have a buddy that does that, and shoots flames 10 feet into the air.

[jleslie48]

I was going for minimal. I don't generally pack a leaf blower when camping. Gas or electric, Not that I even have electricity when I camp.

[jleslie48]

On galvanized steel:

"I read a recent post which mentioned galvanized pipe and toxicity and realized this is a persistent myth in stove circles. I have a background as a chemist, my work includes machining and fabricating, and I think I know enough about galvanized to ease some fears and help dispel the myth.

First, galvanized does not give off 'cyanide fumes'. It DOES give off zinc oxide fumes, which can cause metal fume fever. Metal fume fever is an immune-response condition that goes away in a day or two as your body absorbs the zinc. It's rotten, much like the flu, but it is rarely fatal, usually only when the exposure is extreme and the person has a pre-existing lung condition. It happens to welders all the time, almost considered to be a standard occupational hazard. Welders who work in a enclosed environment and don't wear protection develop resistance rapidly.

Second, galvanized steel rarely gets hot enough to create said fumes except under conditions of welding, grinding or casting. During a stove test, I managed to oxidize 4' of my galvanized flue (it was under a fume hood, just in case). White oxides formed on the pipe but none was released into the air as fume. The fume is extremely visible when welding on galvanized material, as thick white smoke.

Zinc boils at 907C, ZnO at 2360C, and rapid oxidation occurs at much lower temperatures near the melting point of zinc (420C). Once the zinc has been converted to oxide, it is safe. Your stove will never reach 2360C without forced air or oxy mix. I personally use a fully oxidized white zinc-coated elbow as part of a stove I operate indoors, and it is completely inert. I have never experienced metal fume fever myself as I always am sure to have good ventilation and a respirator if I weld galvanized material.

I think galvanized is actually a better material for heat risers if you wish to use thin steel. The layer of zinc oxide will help protect the steel from oxygen and heat damage, I always use galvanized for heat risers in my small stoves and it seems to hold up very well. I always fire them gently at first to oxidize the zinc rather than melt it into a pool at the bottom of the riser. Any oxide fumes will find their way out the flue and not into anyone's lungs.

Finally, galvanized steel is commonly used, within code, as an exhaust duct for gas appliances (go look at your hot water tank or furnace) and even to BUILD WOOD STOVES!
Ex. www.rileystove.com/products/stoves/riley/flap-jack.html is constructed with 18ga galvanized steel! No Riley customers have died yet!"

[leafdude]

Nice project! It's pretty cool that you used scrap metal and duct pipes. Correct me if I am wrong, but aren't duct pipes galvanized steel? I thought these produced toxic fumes when applied to high temperatures?

[jleslie48]

I specifically used Non-galvanized duct work, but you are correct that galvanized steel, using zinc, produces toxic fumes (I'm told) However, as this is a wood buring camping stove, it is used OUTDOORS, so any fumes would dissipate. Also if you are worried, test fire the stove several times to burn off the zinc before using in close(er) quarters.

[Swansong]

I'd love to build one of these for when we go camping! I'm not sure I could trust my husband with it after he turned a chimenea into a blast furnace though. . .