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...

Rocket Mass Heater - Making Some Progress

This morning the world outside the house was frosted with ice.  Inside, we weren't frosted with ice, but it was chilly enough downstairs that fuzzy slippers and a thick sweater are much appreciated.  Getting undressed in the chilly front room where I keep my clothes practically requires a pep talk and a strategy to prevent prolonged skin exposure.  Burrrrr...  We need to finish our rocket mass heater soon!  We have made some progress toward that goal.  In the photo above, you can see the wire cylinder I made to fit around the heat riser.  I used bits of wire that I had left over from building the chicken coop.  

I tried to make it round, and small enough that when the barrel is placed over it, there will be a two inch gap between the cylinder and the barrel on all sides.    

Brandon finished sanding the barrel we burned the paint from.  Since this will get really hot when the stove is lit, we don't want any bits of paint left on it that will make a toxic fume in the house.  

By the way, since I've been asked this by most people who I tell about our rocket mass heater, we do have a smoke and carbon monoxide detector.  It's a fancy one too, that will alert Brandon's phone if it detects anything.  Not that we ever plan to use the rocket mass heater while we aren't there.  And we have a fire extinguisher!  I even got to practice with the fire extinguisher one before, when Brandon's tractor caught fire, so I know where it is and how to operate it.  

We filled the cylinder with a insulation made from perlite mixed with potters clay.  This is the step that I don't really understand the reason for.  The book says it's important, and I think at one time I could glean the reason for it, but by the time we were ready to do it, and Brandon asked me why we were doing it, I couldn't remember any more.  We did it anyway, even though it wasn't a small effort. 

The insulation recipe we used was five parts perlite to one part clay. Brandon used his hands to mix it together in small batches.  It was loose and fluffy, but if we squeezed a handful it would form a clump that would crumble when pressed.  At one point we ran out of perlite, and took a math break while we figured out the cost per quart when factoring in the gas it takes to go all the way to the city for the jumbo bag sold at Home Depot versus driving to the nearest small town Tractor Supply store for the small bags available there.  In the end, it made more sense economically to make the longer trip to the city for the big bag, but I think realizing we could get take out for dinner while there was the deciding factor!  

We didn't compact the insulation mix as we filled the space between the brick heat riser and the wire cylinder.  I would pour the insulation mix in the top, and a goodly portion of it would pour out of the wire onto the floor.  I did a lot of sweeping and reapplying while Brandon stayed busy mixing.  Where the wire met the brickwork around the burn chamber, there were large enough gaps that I used some sand and clay mortar to fill in so my perlite would stop pouring out.  

Finally, we got the whole thing full!  By this point, the many feet we have in the house (twenty, including us, Puck, and three cats) had tracked clay and perlite everywhere, despite my sweeping.  I'm still finding crumbles of perlite in strange places.  

We added a some clay and sand mortar left over from the brick work to the top of the perlite.  I'm not sure, but I think as the stove is used, the heat will bake the clay mixed with the perlite, and create a solid tube of insulation.  I think it may eventually burn the wire away too, but by that time the clay will be baked solid and it won't matter.  

The next step was to place the barrel over the top of the heat riser, and prop it up with some bricks to that the flat top of the barrel is a couple of inches above the top of the heat riser.  Easier said than done!  More math required.  Despite our careful measurements and barrel cutting, we ended up using broken pieces of left over bathroom tile on top of the fire brick to shim the barrel into the right place. 

I was excited to finally get to see the barrel in it's home.  I think some of the folks I've told about the rocket mass heater seemed doubtful that we would like having a metal drum in our dining room.  I know this was Brandon's concern too.  I like it though.  It sort of industrial and unexpected.  A bit weird maybe, but so am I.   It's first thing that can be seen when you walk in our main door too, so I'm glad to find that I don't think it's too ugly.  

I'm pleased with our work so far, but still nervous that it's not going to draft well.  There are some things that we didn't plan for.  For one thing, we always planned to have the barrel near the wall and the fire box out in the room.  When it came time to build it though, we turned it around so we could stand nearer the hot barrel and get it further from the sloped ceiling and wall, which puts an extra bend in our exhaust pipe and may change the air flow to the fire box.  Also, the two inch gap I planned between the barrel and the insulation cylinder, in actuality, varies from one and half to three inches.  Also, the heat riser is off level by at least a quarter inch, but we made the barrel level.  I think this will make the top of the barrel have a hot spot, but I don't know.  I just don't know if these things matter, and I won't know until we light it.  The book says to make adjustments, but that's not going to be an easy thing.  Hopefully we will find out soon, and take the chill out of this house.  Next is attaching the barrel to the exhaust using sand and clay.  I'll let you know how it goes.  

Rocket Mass Heater - We Have Begun!

Happy Thanksgiving everybody!  We had a grand one (five pies, even!), so to to help ourselves recover from days of cooking, eating, visiting, and imbibing, Brandon and I began one of our most ambitious projects - a rocket mass heater.  If you've traveled the interweb in search of alternative solutions to heating your home, you've probably seen references to this type of do-it-yourself wood stove.  It's supposed to be super efficient, heating a small well insulated home, like ours, with a fraction of the wood needed for a traditional wood stove.  It's also a snugly stove.  Because it has a big thermal mass in the form of a bench made of mud and sand, it's made to be a warm seat, which I hope will be perfect for reading books, drinking tea, and cuddling the cats.  Now, with winter knocking on our door, we're trying to get this stove installed in the house.  The picture above is the mock up we built outside for our test run.  It works!  

Brandon marked the bricks and made some drawings of our mock up so we could re-create it inside.  So far, the most challenging part of this project has been finding the materials.  Since we are lucky enough to have friends who are potters and kiln builders, we were able to get some good fire brick to build the burn chamber and heat riser.  

We dug clay from the yard, and also used some potters clay to make a brick mortar with sand we bought from Lowe's.  

The instructions in the book suggest using your hands to mix the clay and sand.  A drill with a mixer attachment works well too.  

The yard near the barn resembles a brick yard right now.  It also rained the entire weekend, so the recent excavations Brandon made for some electrical work have turned to muddy trenches, and the frequent trips out for materials during this project made a muddy mess of the yard and the floors in the house.  We haven't even begun mixing the clay, sand, and straw to create the giant thermal mass bench, and this is already a messy project!

Why is that no matter how careful we plan and measure, nothing ever works exactly like we thought?  Despite Brandon's careful drawings, the mortared structure isn't exactly like our mock up.  Cross your fingers that when we finally light this thing in the house, it drafts like we hope.  

In this photo you can see that we used non-flammable cement board on the floor, then a layer of insulating soft brick used in kilns.  The inside of a pottery kiln can get thousands of degrees and the brick stays cool enough to touch on the outside.  These brick are really light and porous.  The third layer shown here is made from the hard fire brick, and this will be the bottom of the burn chamber, where the fire lives.  

The sides of the burn chamber are fire brick mortared together.  Nice and level, and square.  

The mortar Brandon is using is the potters clay mixed with sand.  Brandon had to fiddle with the amount of moisture to get it to stick to the bricks.  We've never done much brick work before, so this was a new experience for us.  Brick laying is heavy work!  

On the left side of this photo is the hole where the fire wood goes in (straight down).  On the right side is the hole where the hot gasses go up.  In the middle is the brick work that makes the top of the burn chamber, since the fire burns horizontally in this type of stove.  This is the part that didn't fit together the same as our mock up.  We knew how big to make both of the holes, but somehow the brick layout between these didn't fit together like we thought it was going to.  This makes me nervous that the stove might not draft as well as our mock up.   

Have you ever used perlite before?  It's the little white stones that are in potting soil.  It's a light porous rock that not only helps with soil compaction, it also is used as insulation in masonry projects.  To protect the wall and to prevent our hard earned heat from seeping into the wall, we put a piece of cement board along the wall with a gap behind it, and filled this gap with loose perlite.  

The exhaust pipe for this stove is eight inch duct work, that will run along the floor in the dining room, against the insulated wall, and be covered with cob, a mixture of mud, sand, and straw.  

Right behind the burn chamber, where there will be burning sticks, we also put a layer of soft brick against the wall.  

This is the semi- final layout of the brick work for the burn chamber.  Fire wood goes in on the right, near the wall, flames go through the center, and hot gas and bits of ash go up on the left into the heat riser.  

The next step was the mortaring of the heat riser.  This is a short tower of bricks that direct the hot gasses up.  

We tried to make sure the inside of the heat riser was as smooth as possible.  And even though we checked for level as we were building, somehow in the end, it's off level by at least a quarter inch.  Sigh.  What to do?  We decided to ignore it and hope it doesn't matter.  Good idea!

Despite the rain, we kept a fire going outside using wood scraps from the house renovation, and burned the paint off of a fifty gallon drum that was used for spaghetti sauce.  This metal drum is a critical part of the rocket mass heater.  

After the paint was mostly burned away, Brandon used a sanding pad on his grinder and gave the drum a cool looking sheen.  

As you can tell, the cats were very excited by the prospect of a rocket mass heater.  Snore.  

We put more concrete board on the floor were we think the exhaust pipe and the cob bench will be.  Stay tuned for the next installment of Rain and Brandon build a rocket mass heater! I know you are on the edge your seat.  Me too!

Solar Powered Cat Warmers on the South Side

We've got solar powered cat warmers!  The windows on the south side of the house are really appreciated by the cats for their warm winter sun beams.  Unlike the windows on the north side, which only let in drafts.  The cats spend the day while I'm at work in the front room, snoozing on blankets in the windows or watching the birds in the pear tree.  

If I can't find the cats there, then there's a good chance they are upstairs in the bedroom soaking in the sun on the bed or on the carpet.  So far, the upstairs room of our house is always warm, even without any heat.  When we were tearing out walls during our house renovations, we knew that removing the walls and doorway from the stair well, and raising the upstairs ceiling, was going to make it hard to keep all the warm air from just rising to the top of second floor.  We did it anyway, so I'm curious to see how the winter plays out.  If we spend all our time upstairs this winter because it's too cold downstairs, we may have to consider some options for changing the air flow.  

I really love the way the upstairs ceiling looks with the sloped wood ceiling and the exposed beams - but what do I do to block the view?  I hang wet laundry up there to dry.  Doh!  Oh well, only when the weather forecast says it isn't a good idea to use the clothes line outside (so practically all winter, right?).  I just can't resist those beams which are perfect for supporting a rod to hold the wet clothes, and all that dry heat and solar exposure dries the clothes well.  

The only downside to this system, other than marring my view of the pretty ceiling, is lugging baskets of laundry up the stairs.  I made a point of storing all our clothes downstairs when we were planning the use of this house, because I wanted, for once, to have a bedroom that didn't include a laundry pile laundry baskets and didn't want to carry laundry upstairs to put it away, and now I find myself taking laundry upstairs and then back down again.   I don't mind it though.  And the cats think hanging laundry in the house is a great game.