>>979200When properly designed they are more effective than most other stoves. Even the one in
>>979196 isn't 100% properly made since the top flames should be on the top of the unit. Efficiency is measured by smoke more than anything. A complete burn of flue gases is most efficient.
The biggest problem is that there are sooooo many improperly designed stoves online and those styles are perpetuated simply because of ignorance. One other example is the rocket stove. Most of the DIY ones you see are completely incorrect. A rocket stove needs an insulated flue and near complete burn of flue gases. The secondary burn of the flue gases ensures there's no smoke and there's no flame hitting the cooking vessel. Most DIY "rocket stoves" are far too short and/or are not insulated. While those incorrectly designed stoves are still more efficient and easier to use than a standard hobo stove, they are still incorrectly named. I suppose their correct name would be something more like "bottom-fed hobo stove"?
Correctly designed rocket stoves also have the problem in that they are more difficult to control the feeding of fuel in respect to air flow. If they are feed too much they will reduce the air flow to the point that the flue gases are not completely burned and smoke will start. A well maintained fire in a proper rocket stove won't blacken the bottom of the cooking vessel. A properly designed woodgas stove never has this problem since the fuel is loaded as a batch of fuel and its feeding doesn't need to be specifically controlled during cooking.
tl;dr if there's smoke it is inefficient. If the flame touches the cooking vessel it is inefficient.
