Make Better Rocket Stoves with this Free Tool

Hey stove makers, how’s that title for click bate?

As I try to build better diy stoves I look around the internet for inspiration and I see many rocket cook stoves that have missed basics (like an insulated burn chamber) or are built out of materials that will be short lived (such as metal burn chambers). I’ve built a few of these stoves and they do work but are short lived and/or probably not nearly as efficient as the ones originally designed and tested by Larry Winiarski.

So I’ve been working on a design tool to get better results. I wanted an assessment tool that would quickly give me an idea of how well a stove works without lighting it and ideally before I even build it.

There are several rapid assessment tools that are used in health care. These help to give a standardized and rather objective score to what would otherwise be a lot of subjective findings. The Glasgow Coma Scale (GCS) is probably the most common of these. It scores a patient’s level of consciousness on a standardized set of criteria. If you’re posting on premies, you’re a 15/15. But if you’ve fallen off a Wofati and hit your head your score might be much lower. Research has correlated GCS scores to patient outcomes. A GCS score of 8 or less and your chances of survival drop.

I’m from Ottawa so I’ll call this the“Ottawa Rocket Stove Scale”. It is for rocket cook stoves. Instead of a numeric score, each stove gets a letter grade like in school, so it’s easy to understand. It takes about a minute to score a stove.

Each stove gets points for following Larry Winiarski’s basic principles of rocket stoves. If you’re not familiar with them, you should check them out. http://www.bioenergylists.org/stovesdoc/Still/Rocket%20Stove/Principles.html There is much more to a rocket stove than an “L” tube!

Then you subtract points for using materials that are not durable (ie portland cement) or sustainable (ie expensive). Lastly you convert your number value to letter grade for your stove.

I find it pretty easy to use but then again I created it so tell me what you think. The letter grade might seem like an extra step but it makes a lot more sense than saying that your stove is a “3” since most folks are familiar with letter grades anyway.

To give you an example of a Grade A stove, look at this stove from Approvecho:

So far I’ve figured out that my best stoves are in the “D” range. So now I can “Fail better” in my designs and easily see how to score more points which translates to a better stove.

I’ve found this useful so far but am wondering if any of the rocket gurus on premies have any feedback? Does it seem accurate to you? Let me know if you find it useful or think that it needs tweaking.

-Ottawa Tinkerer

Here's an example of the Ottawa Rocket Stove Scale used to evaluate one of the stoves that I use at the land. I'e updated the scale slightly since I shot this. Despite only scoring an "E" the stove does work quite well and we've used it to cook many meals and even to heat a branding iron for decorating wood.



Let me know what you think... especially is my geometry correct? I pulled it from somewhere at some point and wrote it down but can't find the reference any more.

-Ottawa Tinkerer

OK, here's another example of the rocket stove scale rating one of my stoves... This one is cast in a portland cement and perlite mix and finished with standard mortar... a first attempt at using it for a finish. This stove scores a "D" on the scale (assuming I put in the shelf for the wood that I forgot to include in this photo)

Anyone want to see how their stove scores?

This looks like an awesome tool!  I have no comments, just stumbled on the principles myself, but it looks like a great start at the very least.  It hinges on whether Winiarski is right about each of these things...and so far as I can see, he's done the most research on this and it all makes sense.  But if I've learned anything here on permies it's that there's always more to learn...and sometimes that includes finding out that everything I think I know about something is wrong.

Also, I guess the clickbait didn't work very well...

the other thought i've had is "heat the thing, not the air"--this principle is the main one I think of when i think of heating in general.  Conductive or radiant heat first before convective.  But in Apropechio's cook stove's case, I don't see any reference to that.

Now, I get that the problem is that you can't use a low-mass conductive obvious choice at such high heat--i.e. metal--without causing serious problems of pollution and wearing out.  But maybe it could serve in a secondary position? not directly against the flames but somehow conducting heat to the pot?  (on the other hand, the fire itself needs a lot of heat to keep being an efficient fire instead of a smoky one.  It's like having to pay protection money to the mafia, the government, or the vampire-mafia-government.  It just keeps on taking!  But is it better than the alternative?? [by the way, a guy I know just came back from Venice which he said was built by mafia-type folks and was amazing!]).  Maybe you just have to keep feeding the beast and be grateful for whatever crumbs of convective heat it deigns to throw your way.  

(But maybe after the fire is done, you could use the hot coals somehow??)

Also, is it possibly better just to do a biogas digester and not have to think so much about airflow?