Rocket mass heater

rocket mass heater by Ernie and Erica Wisner

During months I have done research on the internet. Most Bulgarians heat their homes – even apartments – with wood stoves. Unnecessary to say this causes a lot of pollution, taking into account that the output of the used stoves does not surpass 20%. That means that 80% of the energy present in each woodblock is just spewed out of the chimney without being used to warm the house.

The amount of pollution created by those thousands upon thousands of stoves is unimaginable. Next to that is the fact that wood is fairly expensive, taking up almost half of the income of the average Bulgarian during winter time.

My first thoughts were to improve the output of these stoves by soldering extra metal parts on the stoves to improve the airflow, so to reach a more complete combustion. That would have been a cheap alternative, but unfortunately the possible gains were too low to consider this option.

Pellet stoves are, due to the high purchasing cost, not worthy to take into consideration as a solution for the common people, next to the fact that pellets cost almost as much as wood over here.

So I ended up reading about ‘rocket mass heaters’. It was, I guess, the name that made me take a second look at the possibility, even if I could not imagine these kind of heaters would be a solution, for I am no rocket scientist. But every man, or almost every man, has some fascination for rockets. So, reading on, I found out it just got it’s strange name because the stove makes a sound just like a rocket when burning.

Because it burns fiercely. When operating and well fed with small branches of wood, the temperature in the secondary combustion chamber can reach up to 1000°C! ?

So last week, after having searched all over the nearby towns, I finally found heat-resistant bricks needed for the primary and secondary combustion chamber. I built a prototype in my yard to test out if the measurements I used for the thing were working as they should. My worker, a guy from the neighborhood who works for me, rebuilding my house and garden, looked at me if I was crazy. In his opinion that thing never would work because it went against all intuition.

I lit it, and after having released a bit of smoke the prototype started making it’s rocket-sound. The flames were sucked inside into the primary and secondary combustion chambers, and the inverted barrel sitting on top of the construction started to heat up really fast. I was in total amazement when only steam came out of the exhaust. It just had a vague smell of smoke, but just faintly.

When the weather starts to improve here we are going to build this rocket-thing in my living room. In the design I imagined in my head there will be a seat like a reclining chair that follows the contours of the body, so people can lay down reading a book with a warm back. Since the material to be used around the stove is adobe all imaginable designs are possible. Inside it run the exhaust pipes which end up in the chimney, heating along their way the surrounding adobe. On the other side of the barrel I will make a bench where a few people can take a seat to heat up their bums and feet.

The big mass of adobe heats up slowly, while the inverted barrel immediately heats up the room just like a classic stove. After a few hours of having made the stove work the adobe slowly gives off the heat that was stored inside it. That way it keeps heating the room more than 24 hours after the fire got killed.

Finally the chimney lets the gasses out, but since all energy has been used to be stored in the adobe, the exhaust is no warmer than 30° to 40°C. Other than water (dry wood has about 20% water in it) and CO₂, along with some chemical elements in wood that cannot be burned (similar to classic stoves), there is no smoke, and pollution is reduced to a minimum.

Since the stove uses between 1/8th and 1/10th of the wood used for a classical stove (the output is around 90%), this will be a huge money saver. Combined with the huge reduction in pollution this is just a win-win situation for both man and nature.

Some locals have already expressed their interest for this project, and if all works well at my place I guess I will help them build one for their homes so they and the environment can benefit from this wonderful (but very ancient) technique. The cost of building a rocket mass heater would be less than 100€, which is much less than the price for a new wood stove as they have them here.

So wish me – and especially my rocket mass heater – success!

The prototype in my yard. Only steam comes out with a very faint smell of smoke. The definitive construction in my house will also have an exhaust and lots of adobe to store the heat. ©yannbastiaans


Take care,

Love ❤️