This is full throttle with the air intake wide open (see bottom left of picture). Probably more than half the heat goes out the chimney this way. With the air intake almost shut, almost no flames inside chimney, so no excess heat up the chimney. To improve power output without wasting energy, I will try to put a "labyrinth" kind of plate inside the stove just underneath the lid to force the flames to spend more time inside the stove, and also to touch more of the cooking surface to make for faster cooking. It is clear that you will need a glass fibre fabric piece in your tent wall to lead the chimney through; I accidentally melted a PET bottle that was standing a good half metre away from the chimney.