Rocket Stove: The Thermal Battery

Urbanite & Cob Bench

The Thermal Battery building has begun! That is, the cob and “urbanite” (repurposed chunks of sidewalk etc.) bench and bed the exhaust pipe is buried in. It will hold the heat and slowly release it back into the room.

More bench added
Bare pipe and piles of urbanite
Nathan made an impression.
Pipe exiting through the wall will not be visible after the bed is built.
Robin, racing through the steam. Yes, only steam!

Rocket Stove, Go!

Part 3: Insulation and the Barrel

Insulation: perlite & clay slip
Pour insulation between stack and hardware mesh.
Burn the paint off the barrel.

Up-end barrel on stack.

Under that slab of marble is the manifold. It’s a space between the bottom of the barrel and the first length of stovepipe.

Here is a better picture. And another. From people who did a better job of remembering to take photos.

The feed (fire box)
Stovepipe snaking through future cob furniture
A "tee" in the pipe for ash clean out

I left for the day and returned to a blazing fire in the cob house! Pah!

Rocket Stove Adventures

Part II: Level, you elusive devil.


In The Book, there is a mere few sentences about starting on a level surface. Of course, it is common sense. The stack and burn tunnel need to be straight and smooth, so, level.

However simple the idea, the task was in no way easy.  Our floor started out level, tamped drain rock. Then we made cob and built walls in there. Over time, globs of cob fell and built up. We walked over them and stomped out cob on top of them, forming little hills and valleys that had to be scraped level without disturbing the drain rock below. Not easy.

So, I am dedicating this entire post to the topic The Importance of Being Level.

Marble base (it's a all about that...)

We dumpster dive for chunks of granite and marble. Laid out with mortar, this one-inch marble will collect heat under the stove and lend it to the floor.


Kind of a shame this beautiful stuff will be below floor level. (The floor will be a cob floor with a beeswax finish.)

Earthen mortar

We mixed small batches of mortar in one of Nathan’s water drum troughs, usually used for soaking clay. Mortar is made of strained construction sand and clay. The sand needs to be sharp and fine, aka masonry sand.

Pea gravel

Nathan used an old kitchen strainer he scored at a thrift store.


We used the course sand to set the marble slabs.


And spent hours trying to get them level.

At Last! The Rocket Stove Construction Begins

Part One: The Mock Up

First of all, this whole idea we got from Ianto Evans, stove-master and co-founder of The Cob Cottage Company in Coquille, Oregon.

Here is where we begin. This is our mock-up furnace. It’s for an 8″ stove pipe system. After we mortar it together, we will up-end a 55-gallon steel drum over the stack.

It took a couple tries to get it just right.

We build a fire in the feed, or fire box and got air is drawn through the J-shaped chamber and up the flue.

The test fire

It will meet the barrel and be forced downward through the stove pipe, which will be embedded in “thermal batteries” where the heat will be held and slowly released.

Rockin heat

Thermal batteries will be formed into benches and a bed. I’m excited to say goodbye to cold sheets. But I get ahead of myself.

A Tour

Welcome to our yurt at Spider Springs! It is 16 feet in diameter. A perfect size to keep warm and light up easily. We sectioned off the circle into “rooms” that flow into each other. More accurately, they smoosh together.

We have changed it since these pictures were taken. We raised the bed on a 3-foot platform and use the space under it for storage. The rocket stove, now in January, is surrounded by stacked wood for drying. And we moved the shelves near the “closet” under the bed and turned the clothes more against the wall so we could move the chairs closer to the wood stove. We’ll get some updates up as soon as we get a new camera.

yurt door

Come in…


Our rocket stove (The Pocket Rocket)


The kitchen/bedroom


The bedroom

living room

The living room


The closet and exit

That’s our little home. Outside is an outdoor kitchen, which was awesome in the summer! But when the serious Northwest rains and wind came, it was much less awesome. We tend to open the dome all the way and use a small table top Coleman inside for almost all our cooking.

nathan in the outdoor kitchen

We are working on a bigger one closer to the cob site with north and east facing walls, the cob oven, a wood stove and a dining area. Spring, spring, come quickly! We’ve got so much to do!