Rocket Mass Heater - All The Pieces

This weekend we made major progress with the rocket mass wood stove we are building.  This is what it looked like when we stopped working on Saturday evening.  All the major pieces were in place, including a mixture of clay and sand used to attach the inverted metal barrel over the heat riser to the eight inch duct work.  This was the part that was the hardest to wrap our brains around during the planning stages of this project, since we weren't sure how difficult it would be.  Turns out, the only hard part is mixing the sand into the clay.  Sculpting it was fun.  

When we first put the barrel over the heat riser, as I showed you before, we used bricks and bits of broken tile to shim it into the right location.  Once I started putting the mud around the base though, Brandon cut some bricks to the correct size, so we could prop the barrel stable in three locations.  I'm sure the dried mud will sort of hold the barrel in place too, but we wanted it to have a pretty firm seating, just in case it gets bumped.  We removed the brick column with the tile shims once the cut brick props were in place.  If you can tell from the photo, I'm basically sculpting a wall of mud that leaves a space against the heat riser for the hot gas that fills the barrel to enter, so it can be directed toward the exhaust pipe on the other side.  

The cast iron dragon on top of the barrel was a gift from my parents.  It holds water, and when the water gets hot, the steam will vent from the dragon's nostrils.  How cool!  I've read that this type of stove makes a roaring sound, like a dragon.  I can't wait to hear it!

Here you can see the two brick support posts we made, and the beginnings of my mud work.  

I didn't get fussy with the surface of the mud on the outside, since this will be covered with cob later, but I tried to keep the inside of the mud as smooth as possible.  

For this part of the project, we were using four parts sand to two parts potters clay, and the clay was pretty soupy since we filled the buckets with water a few weeks ago.  We used the drill with a mixer attachment or a hoe in the wheel barrel.  It was work to mix it together.  

To make sure nothing was going to be shifting much after I put the mud in place, we assembled the rest of the exhaust pipes that will eventually be covered with cob.  As you can see, the exhaust runs from the heater, all the way to where I'm standing at the door, turns, and runs about half way back before exiting the house through the wall.  

There's an ash clean out near the heater, one in the turn, and another outside, at the base of the vertical stack.  These will have caps over them, to the disappointment of the cats, who have enjoyed having tunnels to play in.  

We used sheet metal screws to hold the pieces together.  

Then came the hardest part - cutting a hole in the wall.  It wouldn't have been so hard if we hadn't selected a spot that was crossed by a two by six, which Brandon had to cut through.  I heard a lot of grunting and muttering during this process, so I was glad to be busy making sand castles, er... I mean, working on cobbing the barrel.  

The chickens came to investigate the hole.  I was waiting to see one pop inside for a visit.  

Finally, all the pieces of the exhaust system were assembled. We used bricks to hold it off the floor a little.  Heat rises, so I wanted the exhaust pipe to be as close to the floor as possible, so the cob bench can absorb more heat.  

Outside, we placed a cap on the clean out, and a vented cap on the top, so no furry or feathery friends can find their way inside the stove.  That would be bad.  

I took this photo before I closed up the last of the mud around the barrel.  Here you can see how the mud encloses the open end of the exhaust pipe, and the gap I've created with the mud wall.  Supposedly, this is where the most ash collects.  We have several inches of space below the exhaust pipe, hoping that it will be a long time before it piles up so far it causes a blockage.  Since our clean out is very close, I'm hoping with the air compressor and the shop vac, I'll be able to reach inside here and blow and vacuum any accumulated ash piles.  

We went to bed Saturday night with a plan to light a fire the next day.  Oh, the excitement!  And guess what happened Sunday morning?  It worked!  Sort of...