Three stone fire

This is the typical cook stove in Malawi and in many places around the World really. A pot like this is placed on three stones or bricks and food is cooked.
As you can see from the flames much of the heat produced from the wood fire escapes.
This is a bit of an experiment to compare this with a new stove we are in the process of designing. We weighed the wood, brought the water to the boil and weighed the unburned wood. Then we had the 4 litres of water as a constant of water and compared weight of wood used in the various stove types and the time taken for the water to come to boiling.
We are working on a few insulated versions and see what we come up with.
We are currently trialling one possible arrangement with 200 of our most influential women.
Oh the women can do the construction and it costs nothing to make!!

The first numbers:
The three stone stove burned 0.7 kg of wood to boil 3 litres in 25 minutes, while the improved stove used 0.3 kg of wood and took only 13 minutes.
A 57% improvement on energy efficiency!! Something to go on.