OK, I'm relatively new to the permaculture world, and I know that concrete block rocket stoves as seen on Youtube aren't exactly green, nor efficient, nor much of a rocket. That being said, I like trying new things and wanted to give it a go. Right now all our time and energy when we get out to our property is devoted to building our house so we can get moved out instead of having to drive back and forth on days off. I love bbq, and I love cooking outdoors, so once we get moved into our home I'll be building a pavilion constructed similar to a Viking or Saxon house to house a rocket oven, rocket stove, smoker, and grill. We use our fire pit or my little Weber grill to cook when we go out, and I thought since I already have concrete blocks, why not give a concrete block stove a go. I know the concrete blocks won't be very durable, put at $1 each I'm not out a bunch of money. Any damaged or destroyed blocks will be broken up and added to the rocks around the driveway culvert to prevent erosion.
I used a masonry disc in my angle grinder to cut the end out of one of the blocks, the proceeded to crack the block when taking out the end that I cut. Oops, but at least it doesn't pour smoke out through it. I decided to use 5 blocks instead of 4 so my pan would be up higher and I wouldn't have to bend over. I squished a piece of 4" duct that I had lying around so that it had a flat top. That was put into the burn chamber and sticks placed of top of it. The thought was that it will provide a channel for combustion air to be drawn it under the fuel. I had a terrible time getting it to burn at first. I took the top block off and was able to get a good fire going. When I put fifth block back on, it continued to burn well. I was impressed with how much heat I was able to get out of twigs and small branches I picked up off the ground. It was much more efficient to use for heating a pan of beans than the fire pit. Instead of using several logs to get enough fire for cooking, I used a bunch of sticks I picked up off the ground. Pretty cool!
Learn to dance in the rain.