Rocket Stoves are not complex but they are very efficient. They burn most of the gases that are given off by the burning fuel, thereby producing more heat per amount of fuel than other types of stoves.
This has the added benefit that they do not use as many fuel resources and do not pollute as much as other types of stoves. And they are very cheap to make. It is possible to make one for free.
Some people combine a rocket stove with a thermal mass so that the mass will retain the heat after the fuel is no longer burning and slowly release the heat.
Youtube is crowded with rocket stoves now. There are all different kinds. The two main kinds are metal or ceramic/brick.
The metal ones do not last very long because the fire in them is so hot that it soon burns up the metal. I read that their average life span is from about a month to three months. If the metal is heavier, they can last much longer, however.
LDS Prepper has several videos on youtube that show how to build a rocket stove from tin cans and a little sand, ashes, or vermiculite. His videos were the earliest rocket stoves on youtube and are still around. This is probably because his videos are very clear and easy to understand. One of his videos shows precautions to avoid injury when you make a rocket stove like his. You can cut yourself badly or get other injuries if you are not careful.
I don't believe LDS Prepper mentioned that you need to keep an unvented rocket stove outside. They are efficient, but nothing is perfect and it would be awful if you died from carbon monixide poisoning caused by your emergency preparedness equipment.
The main tool you need to make the tin can rocket stove is tin snips. If you have those, the stove can be almost free. I will post more later on some rocket stoves that are free, not almost free.
It concerns me that people who use dial up or other slow internet may not be able to see the youtube videos on building rocket stoves. I plan to write and draw instructions for making one that can be printed out or read without downloading videos.
Some enterprising souls have already begun making and selling rocket stoves. I think this is very good. People have a way to make money. Other people can buy a rocket stove to save on their fuel costs. The little tin can ones have been selling for $25.00 in one place. All different versions have been proliferating all over the internet. They are not hard to find now.
I am working on adding contextual ads to this blog. That should mean that ads selling rocket stoves will probably be on here soon. I like that. It means you get to look at things you are interested in. I am not a very technically proficient person, so it may take me a while longer to do this.