A big component of our stove is its insulation.  Between the inner chamber (where combustion happens) and the outer walls is a lot of space.  If we simply left it empty, then hot air would move around and carry heat from the inside to the outer walls in much the same way your oven cooks food.

The obvious answer is to use insulation.  But what kind?  Often ceramics, sand, and earth come up.  It’s true that these would slow down the transfer of heat from the inner wall to the outer wall, but they do it by absorbing energy.  In scientific terms, they have a higher specific heat capacity than air which means that, for every degree they change, they absorb more energy.  This is helpful for safety, but it can actually decrease the efficiency of a stove.

In order to have an efficient stove, you need materials that don’t transfer heat very well–or, in other words, materials that are not very thermally conductive.  Air is actually pretty good with respect to this, but it’s a problem when it moves around freely.  Many of the best insulators simply work by trapping air in small pockets.  This is how down blankets work.

Our initial prototype used perlite, but it’s not readily available in Myanmar, so we’ve been exploring the possibility of importing it and other materials.  Ash is readily available and a pretty good insulator.  We’ve also been looking at special clay mixtures which are much lighter (and thus have a lower specific heat capacity) than normal ceramics.

As always, we’d love to hear from anyone with thoughts/advice on the manner!

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.