When we arrived, we spent a while admiring, and then firing, the homemade rocket stove mass heater, www.rocketstoves.com, that David and Maureen had just finished building in one corner of the living room of their strawbale home.
Rocket Stove Heater and Base Layer of Earthen Floor
The heater consists of a small feed barrel (closest to the door), then a larger 55 gallon drum which conceals an internal, insulated, firetube heat riser, then a long section of piping that serpentines through an adobe block and cob masonry bench with flue cleanouts (the bench that wraps around the corner to the left of the 55 gallon barrel), and a chimney.
Rocket Stove Feeder and Burn Barrels
Above is a closer view of the smaller (20 gallon?) feed barrel on the right, and the larger 55 gallon barrel that conceals the heat riser tube. You feed sticks into the small barrel on the right. They burn at the base of that barrel in the start of a masonry, fire-brick-lined horizontal passage. The hot gases then rise up in an insulated tube inside the 55 gallon barrel, hit the top, then cascade down around the annular space between the concealaed tube and the outside of the barrel, then into an 8" metal stove pipe that heads out through the mass bench.
Rocket Stove Mass Bench
Here's the mass bench. It has two cleanouts - one at the start just to the left of the barrel, and one at the far left end of the bench, where the internal pipe does a U-bend to head back though the bench, along the exterior wall, to the chimney.
Rocket Stove Feed Barrel
Here's a view looking down the feed barrel into the start of the masonry burn passageway. The loose brick atop the burn passageway opening is used to control the amount of draft to make sure you don't get smoke coming back up the feed barrel. When the stove is operating, there will be several pieces of wood stuck down into this barrel. The wood burns at the bottom where it sits in the burn chamber below the brick.
Unlike regular wood stoves, which often control the rate of burn by restricting the combustion air, a rocket stove burns wide open, with as much air as the wood needs to burn efficiently. Restricting stove airflow causes the wood to burn less efficiently and produces pollutants. A hot fire with plenty of oxygen produces very little pollution and burns more efficiently. The 55 gallon barrel releases heat instantaneously, and any excess heat is absorbed from the horizontal chimney by the mass bench. By the time the flue gases get to the vertical chimney, they've cooled to the point that you can easily put your hand on the chimney without burning it. The mass bench then stores the heat, and releases it for hours after the fire has burned its way out.
While we were there, we fired the stove for the third time since they'd built it. We only ran it for about 30 minutes, but an hour or two later we could feel the bench surface beginning to warm as the heat slowly conducted out to the surface, long after the fire had gone out.
I think what we like so much about this stove is that it is entirely experimental and completely owner built. If you build it wrong, operate it wrong, or don't use common sense, the results could be harmful, to you or to your home. If you work carefully, test things as you go, and use common sense, the result is a heating device that costs a few dollars to build, pennies to operate, is beautiful, and offers performance on par with custom built masonry stoves that cost upwards of $10,000. It requires a different mind set than the conventional one a lot of us are used to, where we're dependent on others for expertise, and as a result, pay others to meet our needs for us. Rocket stoves rock!