A year ago, after we had just completed a prototype of a stove design we liked (it was literally made from an old metal trash can!) we decided to try adding a “pot skirt” to see how much it would improve our stove’s efficiency. We had read about these heat shields in other stoves before; the basic idea is to surround the pot on all sides with a thin metal shield that creates about an inch-gap for hot air to pass through. The pot skirt thus prevents heat from the stove from escaping to its surroundings, keeping it close to the walls of the pot and increasing the heating surface.

The idea sounded interesting, so we set to work building a prototype and testing it out! (My next post, “Frustrated by Frustums” will explain why our prototype is the shape it is-most pot skirts are actually just cylindrical.) The result was… WOW.

Adding the pot skirt cut down our rocket stove’s boiling time almost in half. The rocket stove itself was already able to boil water in maybe half the time it took an open flame, but with the pot skirt, we were boiling water at incredible speeds: up to a third of the time it takes to boil water on an open flame. Whatever we expected, I don’t think it was as drastic as this.

As great as it may sound though, our pot skirt idea still needs a lot of work. Adding that much material to our stove makes it more expensive and difficult to manufacture, not to mention clunky looking. Because it traps hot air, the skirt metal gets really hot too, posing a potential burn hazard to our customers. Our first prototype didn’t allow the cook to see the flame very well either (we fixed that issue by cutting out holes into the skirt).

Right now, we’re starting to explore new skirt designs, as well as some completely new concepts. One of the things we’d like to try is something similar to a “heat exchanger” which traps hot convective air at the bottom of the pot. The Jet Boil camping stove uses a mechanism like this. Such a design wouldn’t increase our heating surface area, but it will at least increase the concentration of hot air, which may be enough.

If you have any ideas about this engineering challenge, we’d love to hear them!

We’ve been talking a lot about our philosophy approaching this project, but I think it’s time to explain a little bit more about our actual stove technology. The stove prototype we’ve built for women in Myanmar is based on the Rocket Stove created by Dr. Larry Winiarski at the Aprovecho Research Center. Many such stoves have been modeled after Dr. Winiarski’s design, including the Berkeley Darfur Stove as well as other home-made versions (there are tons of videos online for how to make your own).

We chose to adapt the rocket stove design because its use of low mass insulation is very effective at keeping the fire hot and transferring most of the heat to the pot.  In my next couple of posts, I’ll explain how a hot fire and a design that channels heat to the pot are both important for improving the overall efficiency of the stove (I’m trying to keep my posts shorter :p).

If you’re wondering why we chose to design our own version of the rocket stove rather than partner with one of the other organizations that are building them,  please read our post about the importance of tailoring the stove to the local culture.  We aren’t seeking to compete with other groups; instead, we learn from them and share our own ideas. Building on someone else’s great technology also gives us time to focus on equally important issues of manufacturing, marketing, distribution, and education, all of which are crucial in getting our stove into the hands of women.