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!

When you’re working with customers who are miles apart from you, limited to very simple communication networks (i.e. nowhere close to high-tech videoconferencing) and don’t even speak their language, how can you accurately claim that the work you’re doing is human-centered?

Making sure that we understood our customers’ needs at every step of the way was a significant challenge for us, but one that we thought was crucial. We discovered that making prototypes, both here and in Myanmar, was the best way to communicate our ideas to our partners and listen to their ideas in return.

Showing prototypes to our customers helped them tell us what they wanted. When we originally asked what kinds of improvements they needed on their three-brick stoves, we rarely got any definite answers. These women had been cooking on an open flame for centuries, and they had developed all kinds of “workarounds” to make full use of the technology; it was often hard for them to articulate what they wanted to change. Setting our prototype in front of them gave them something to evaluate, and opened up the conversation about which features supported or conflicted with their culture of cooking.

Not counting low-resolution prototypes and partial ones, we’ve made about 16 working prototypes of our stove thus far. Typically, we come up with a revision to the design, draw up some plans and explain how to make it, and our partner builds a prototype in-country. They then tell us what they discovered from making the prototype, what changes they suggest, and what customers have said about it. We take their feedback, prototype their design ourselves, and make revisions. This constant iteration helps us make sure that we are attuned to our customers’ needs at every step, even if we can’t be close to them always.

During our trip to Myanmar last year, our team created a set of cook stove prototypes  that rural women could try out in their cooking spaces.  We created two prototypes–one box-shaped and one bucket-shaped–that we took to women and asked them to compare.  We asked them: do you prefer the box or the bucket stove and why?  Which one would you prefer to use and why?  What does a bucket stove make you think about?  Have you seen something like this before?