2018 Rocket Stove

25th January 2019

Great video showing the rocket stove in detail

The rocket stove was built in July 2018. Experienced rocket stove builder Jordi taught us how to create an efficient heater out of very simple and locally sourced materials. All we used was an old metal drum, metal L shaped pipe, bricks, tiles, soil, sand and straw.

The rocket stove has 2 major parts. The fire is fueled in the L-shape, the hot air goes up and then it’s sucked down on the sides of the L-shape and into the second part of the rocket stove. The horizontal part of the chimney doubles as a heated bench ( permaculture thinking; stacking functions!). Because the whole structure consists of a lot of mass, once it’s hot, it will stay warm for a long time slowly releasing the heat.

That’s as far as the theory goes. Reality kicked in when we lit the rocket stove for the first time… After building the stove in July, we first lit it in October. It was about 30°C outside so it was easy to collect some dry branches and off we went. Result; smoke coming out everywhere. The whole structure had developed small cracks as the organic “cement” made out of sand, soil and straw had dried up and started cracking. Now the stove was venting inside the house. It was horrible. So time to get a bucket with water and some clay and a brush to patch up all the cracks and holes. This gave the rough looking structure a smoother look. The next time we lit it the smoke wasn’t as bad and we could fix the cracks as the fire was going. That was an easy fix.

Time passed by and when hurricane Leslie came we knew for sure autumn had arrived. So I decided to light the rocketstove to warm us up and dry our clothes. Lighting it is not an easy job since the L-shape is only 22 cm in diameter so I had to use very small branches to make sure enough oxygen was available for a good combustion. I also noticed that the opening of the L-shape was too low to the ground to sit comfortably in front of it. I almost have to lay on the ground (this reminds me of roman style eating where rich people laid down while eating…) to feed the small branches into the opening. Note to self; if I happen to build another rocket stove, it needs to have an opening on eye level. But I soon learned that wasn’t the only problem…

Some days the smoke comes back into the house, even accompanied with flames. The rocket is supposed to rocket upwards, not straight into the house! Soon I realised this was caused by two problems. The first problem is the existing chimney built on the roof of the house. A short (2 meter) chimney sitting on top of a flat roof deep in a valley doesn’t catch much wind. There is some draft around the chimney needed to create an underpressure inside the chimney to direct the smoke in the right direction. So one day we had someone on the roof to wave a towel around next to the chimney to create some airflow. This was surprisingly effective! This poor person standing in the roof had to stay there doing the “wellness centre towel wave” until the hot air made it through the horizontal part of the chimney into the vertical part, where the rising hot air would find it’s way out. Not to self; the shorter the vertical part inside the house, the sooner the stove has the rules of physics working with it. If the inside tubing was shorter than the approximately 7 meters of vertical chimney we have so the whole system would heat up faster.

So a lack of breeze in combination with a short chimney on a flat roof down in a valley is not ideal. But the opposite, strong winds, caused problems too…

One very windy day I tried to light the rocket stove but the wind created so much draft inside the system that the starting fire would go out immediately. It took me a lot of effort to get enough heat in there (between wind gusts) to get the rocket stove going. But as soon as I was going it went off… like a rocket. The roaring sound was immense and perfectly synchronised with the wind gusts outside. But sometimes the wind would change and instead of creating an underpressure in the chimney, it would blow down in the chimney full force and I had the flames with the force of the rocket INSIDE the house. Luckily this nasty habit stopped as soon as the whole heating system was hot. But until then, note to self; make sure to have a good fitting door to close quickly if needed. Luckily, the curved removable door we have proved to be very effective.

A few weeks later :

Today, after all the troubleshooting I’m sitting on a heated bench huddled under a warm blanket. Since we light it every day it is very easy to start. I assume that is because it’s not fully cooled down from the previous fire. It only consumes small branches and produces more heat than I could ever imagine coming out of such a small amount of fuel. And the structure stays hot all night long. As soon as I get a house that needs a stove, it definitely is going to be a rocket stove. Now I understand the rocket stove I hardly have trouble with it. The only downside is that it does require tending to produce a great amount of heat… I love fire and making fire and fuel efficiency and environmental benefits make me feel good too.