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Old 12-18-2020, 09:47 AM   #1
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Rocket stove modification

Nearly two years ago I bought an inexpensive rocket stove off woot.com (amazon's closeout site), and while it worked okay, it never was as good as it could have been. The efficiency of a rocket stove greatly depends on the 'draw' effect of the chimney and this one - like most commercial ones - had a pretty short chimney.


That short a chimney made it more susceptible to wind than ideal, where a change in wind direction would make the fire tend to lean toward the feed chute instead of up the chimney, so I decided to extend the chimney some. Couldn't extend it too much, as too much would make it top-heavy and prone to toppling. It was very simple & easy; can't claim any major accomplishment on it. The stove is made from typical 4" square tubing, so I went to a local welding shop and for $5 got a scrap piece of 4" square tubing about 9 inches in length, then at the house I bent & attached a band of 1 1/2" metal strap to it and fitted it to the top of the existing chimney. Added some high-temp black paint to protect it from weather, and that was really all there was to it. It fits tight enough that I haven't bothered to screw it to the original chimney, and not sure if I will or not. Have to wait & see if it settles in any or not, and will go from there. Confess I haven't actually used it since adding the chimney extension, but it's still stable which was my biggest concern, and should be nothing but a positive change on how well it draws the fire from the feed chute into the chimney riser.
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Old 12-19-2020, 06:31 PM   #2
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I went ahead and attached the extension to the chimney just to be safe, and tested it this afternoon. The simple & cheap extension made a huge difference; very happy with it.

https://youtu.be/1vTo-mYrSck

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Old 12-20-2020, 07:24 AM   #3
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Excellent video, I'm betting it didn't take that long to get to a full boil. Just a thought, if you had to vacate the premises quickly, what would you use for a handle where you wouldn't get burned?
 
 
Old 12-21-2020, 06:52 AM   #4
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Nowhere to grab it that isn't hot when in use, but I don't see that as much of a problem. Not a big bugout proponent, but if we had to I wouldn't be wanting to carry that stove unless we were in a vehicle. On foot, not something I'd take. In a vehicle, a person could dump the fire out and it would probably cool off enough in just several minutes to chuck it in the truck or jeep; or even just pick it up momentarily with a gloved hand or with a stick through its handle on the back.

It would have to be something very specific to our area for us to bug out; a forest fire probably being the most likely. But other than that, we're in a much better location than most, as far as number of people nearby, type of people nearby (there's only one non-cousin within a mile that I'm aware of), our location & house itself with a completely isolate-able concrete storm cellar with generator power and plumbed-in yet isolated water tank, etc. Main thing the storm cellar is lacking is central heat & a/c; we've been using a vented portable a/c unit in the summer & small heaters in the winter. But tomorrow the hvac contractor (yes, another of my wife's cousins) is installing a two-ton mini-split unit in it so we can get rid of the temporary a/c unit and heat/cool it a lot more efficiently. That circuit is also wired into the generator transfer switch and is only a 20-amp circuit, so even with the smallish generator, it can be used if necessary during power outages. That will be a big improvement in energy efficiency, both on our electric bill in normal times and in generator load during outages.

But on the stove/bugout thing, if we have to bug out, it's because of something specific to our property like a fire, a toxin-laden aircraft falling out of the sky or something equally unlikely. In which case we'd probably be heading to one of my wife's other 1100 cousins and not need a rocket stove...
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Old 01-03-2021, 11:17 AM   #5
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Even though this thing is an inexpensive & fairly low-end rocket stove, since putting the short extension on it, I've actually come to like it quite a bit. I got to wondering how well it could effectively/efficiently use other fuels besides random sticks & scraps, and wood pellets came to mind. So out of curiosity, I made a mesh basket out of a cheap stainless mesh I bought off amazon. Pellets are only 1/4" in diameter, so couldn't use some 1/2" mesh stuff I already had on hand, at least not without using two offset layers of it. This from amazon is stainless which my existing stuff isn't, so it does have the advantage of longevity, both from weather and fire/heat.

Just cut a piece off the 12"x24" mesh measured to fold up & fit inside the stick feed chute, and since the air feeds in from underneath the fuel, also tapered the in-stove end, making the actual burn area thinner, hoping it would allow for better airflow and hotter burn; thinking this would help reduce ash buildup at the same time. Came out fairly well, and works better than I'd hoped.

Holds maybe a quart of pellets or a little more, which burn for around a half hour if you don't refill it.


The inside end, tapered for airflow and fuel-stacking reasons:


That was after three burns; two of wood pellets and one of cheap ol' roy dog food. The dog food was just to test other organic matter that would feed itself down the slope of the chute. It burned, but not as hot; only hot enough to simmer water, not really boil it. Sounds weird I know, but so much human snack food is good fire starting material that I thought I'd test it out. (Fritos especially are great fire starters. You can light one with a lighter.) The dog food didn't work well, but the cats will eat it. With pellets, there was only about a tablespoon of ash when it was done. With the dog food, there was a lot of ash & crap; not going to try that particular one again.



Don't know yet how long that thin stainless mesh will last. I did buy two of them so have a spare, but if it fails too quickly I may look into a perforated-metal type stainless sheet for a later version. Only time will tell. (Even if I sit around and "think about it" for hundreds of hours, the inescapable fact is, only time will tell how long it will last...) I don't really go camping anymore and so this isn't something I'll use on a regular basis; just something I'm playing with as much as anything. A 40-lb bag of pellets was $7.49 and equals roughly 38-41 quarts as far as I can tell. So 20 hours (probably 40 meals..?) of cooking fuel for less than $8, with no storage dangers as you have with propane, etc, sounds pretty good.

Also noticed that I never mentioned how to light it. You can light it with just about any tinder, typically twists of dry grass, leaves, whatever. Either slide them down the air intake chute below the fuel or just drop them down the chimney before you put the fuel in the feed chute. Either is fine, so long as the tinder is below the fuel. I've done it that way a few times but now I take the easy way and use either an esbit tab or half a trioxane tab. Light it, drop it down the angled air-feed chute below the fuel, and in 7-8 minutes, regardless of whether it's loaded with sticks or pellets it's burning hot enough that it's pretty much completely smoke free
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Old 01-03-2021, 11:50 AM   #6
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You are wasting grass an leaves to start a fire when you could be stuffing them down your pants!
Mel would never use a piece of equipment that nice.
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Old 01-05-2021, 11:58 AM   #7
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I got home early from a customer's house yesterday, and out of curiosity decided to try another substitute fuel. I've read of people burning corn in pellet stoves, so figured I'd try it in the pellet-fuel basket in the rocket stove. The corn was just some leftover deer-feeder corn, in an unopened bag that had been sitting inside (out of the weather) for at least 6-7 months, so it was probably as dry as it was going to be.

Didn't work at all. Normally a single esbit tab or one third of a trioxane tab will light either pellets or stick fuel just fine. I used up two complete trioxane tabs trying to get it to go, and it just would not maintain a flame on its own. Could be an airflow thing; the basket being good for pellets but wrong for corn, etc. But short version, for whatever reason it doesn't work in mine. At least now I know to not count on using it in a pinch; which I really expected would work.

Last edited by John in AR; 01-05-2021 at 12:06 PM.
 
Old 01-05-2021, 12:10 PM   #8
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Quote:
Originally Posted by BigBassMan View Post
You are wasting grass an leaves to start a fire when you could be stuffing them down your pants!
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