Problems with Spanish Rocket Stove

Hi all,

after three months of hard weekend work building our rocket stove up in our isolated hut 3.500 ft high in the spanish mountains, work was almost complete this past weekend, just when temperatures dropped to below frezzing. There is no road that gets to the hut so all the material used was carried in our backpacks and with the valuable help of Petronilo, our neighbor's donkey. Our RMH is a 8 in. (200 mm) unit with a 55 gallon drum (200 liters). Free space between inner and outer drums is 2" (50 mm.) on top and sides. The J-tube is made of firebricks surrounded by steel tube and perlite insulation. Our bench is made out of local limestone joined with cob, and is not finished yet, as you can see in the pics. However, we decided to fire the rocket this sunday for the first time when a snow storm hit the area and temperatures dropped well below zero (celsius).

Firing the rocket was extremely easy, but from the very first moment we noticed it was burning wood really fast and the outer drum was not as hot as we'd expected. Three hours later we had burnt 30 kg of wood and the temperature in the hut (21' x 21') had risen barely 2 degrees celsius. There was no smoke at all and the flame was really healthy! By the end of the day, we had run out of wood and the bench was still cold (the cob was a bit wet when we fired it).

What can be wrong with our Spanish Rocket? Please, help!

My first thought is that your cob isn't dry yet. That moisture will be being driven off and cooling it down. That will definitely impact heating performance.

As far as your rocket "not working" - if it is roaring away then it is doing it's job. The real test is to see how hot your exhaust gases are as they finally leave the flue. If they are cool then the heat is being successfully dumped into the mass of your bench.

Once you have optimised the bench and it has dried out properly you will have a feel for how successful it will be. My thought is that if the building was totally cold to start with then it has a huge amount of very cold stone to warm up (not just the bench, but the walls and floor too). Until they have warmed up a bit as the rocket may struggle to keep the air to a reasonable temperature (sitting on it should still be cosy).

Mike