Uncle Mud here,
There seem to be a lot of ceramics people getting interested in our wood fired rocket kilns. We had a lovely visit with a bunch of you at the NCECA conference in Cincinnati where we stuck an old burned out electric kiln on top of a rocket heater core and fired some pottery in the back lot. That seemed to bring up more questions than it answered so I thought I would take a minute to post a simple explanation of rocket heater technology to you pottery folks and see where that goes.

A rocket heater core is an insulated J shaped tube made out of firebrick and ceramic fiber. It turns small scraps of waste wood into clean heat to warm a house or a shop or hot tub or even a kiln.

The short end is the feed tube. Where the sticks and the air go in.

This middle part is the burn chamber. When it gets hot enough the flammable gasses in the wood evaporate and mix with the hot air in the chamber and cause a violent chemical reaction that produces a lot more heat. In other words the gasses all catch on fire.

Over here at the other end of things we have a riser or chimney. The gasses in the chamber being hot will tend to rise quite forcefully up the riser, pulling more air in the feed tube, heating the air and mixing it with the flammable gasses from the wood and catching it on fire where it being hot will also rise up the chimney there.

Do you sense a theme? We have air and a little fuel and heat mixing and reacting and producing a lot of very hot cleanly burned exhaust. A proper mix of heat, air and fuel will burn hot and clean. Upwards of 2000 degrees F. If you see smoke or soot that is unburned unreacted fuel either because there isn't enough air or because there isn't enough heat to make the fuel and air react completely.

That is the wood burning Rocket Core. If you hang a pot over it to cook with you have a Rocket Stove. If you put a barrel over it upside down and let the heat from the exhaust radiate into the room on its way through you have a rocket heater. If you wrap the exhaust in some sort of mass battery to store that heat and slowly release it to keep the room warm over night you have a Rocket Mass Heater. Here's the part you've probably been waiting for: If you replace the hottest part of the chimney with an old kiln with holes in the top and the bottom you have a Rocket Kiln.

It takes about 2.5 hours and around two banana boxes of wood scraps to fire a 30” rocket kiln. That's a lot better than the 5 hours and $30 to $50 it takes to fire the same kiln using electricity. There are some tricks we've discovered to successfully building and firing a rocket kiln. We'll be sharing what we learn here and we encourage you to experiment and share what you learn too. Plans and kits are also in the works so watch this space.

If you want to follow along or send us money for pizza join us at https://patreon.com/unclemud. You can find always us playing with mud and fire on the Uncle Mud channel on youtube or Unclemud.com.
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https://www.youtube.com/watch?v=YGpLzoQd8s4