When I was 27, I moved back to my hometown in northern Minnesota to start a small organic vegetable farm. I sold produce to the wife of a stone mason, and he was looking for help in the winters. I told him I didn’t know anything. “Don’t worry,” he calmly replied, “I’ll train you.” I learned, of course, that hauling an endless supply of block and stone from one place to another doesn’t take much training. But he also handed me a copy of David Lyle’s history of masonry heaters. Three years later I was working for Albie Barden, building heaters for Maine Wood Heat Company, and dreaming of small things, simple things, handmade things. Albie would feed me all sorts of facts and trivia about little heaters and experimental designs, and then we’d head off to build his next massive, beautiful masterpiece. I loved Albie, and also switched careers, finding contentment in the woods, trading my raucous diamond blade grinders and tile saw for a quiet canoe, axe and knife.
Last summer, I flew out west to take Cob Cottage Co’s complete cob workshop, taught by Firespeaking‘s Max and Eva. The project included a hand-formed, all-cob rumford fireplace, and I put myself right in front of it, working with Max on shaping it with nothing but sand and clay, for me a small miracle of simplicity. When I got home, I told my friend Bill about the experience of finally building a fireplace from raw earth, formed with only the background sounds of song, sculpted with bare hands. He pointed at the forgotten corner of his living room, a cinder block chimney next to splotchy walls hooked up to an iron stove, and said, “There you go. Have fun. Make sure it works.”
We debated the merits of a rocket mass heater for a few days. Mark Maziotti, a rocket heater builder in Missouri, told me, “Rocket heaters are for tinkerers, fire lovers, people who don’t mind some smoke now and then and think it is fun to get down on their knees with a box of matches to mess around.” The next day, Katie, Bill’s wife, breezed into the room and said, “I don’t care what you’re doing, but it can’t smoke.” So it turned into something more familiar to me, with an actual door, a bypass to establish draft, and no salvaged metal barrels. It also became something more expensive.
My goals on this project were to see how cheaply I could build a modern-style heater, to find out how simple I could make it while still retaining the principles of contraflow design, to work by hand as much as possible with minimal power tools, and to avoid the use of cement.
I drove to Maine Wood Heat, rented one of their enormous gaping-dinosaur-jaw-wet-saws, cut the firebrick core and clay flue tile bench, numbered all the pieces, picked up a cast iron door and some gasketing, and drove it all back to New Hampshire. Bill got a couple tractor buckets of clay soil from a wet spot just below his garden, and for the next four weeks his employees found him hard to find at work.
Here’s some highlights:
Course one. The front half of the heater will feed into the bench. The bench then goes back through the rear of the heater, under the firebox, and into the flue (which goes up alonside the cement block chimney before entering at the previous stovepipe opening, which I enlarged with a grinder.)
Course three / firebox floor. Set on a 1/4″ metal plate so that the floor of the firebox is totally removable if it starts to wear out over the years. Sloped common brick in the downdraft channels directing gases to front half of core.
Finished core and bench. To be clear about this – the gases go up the firebox, hit a refractory cap, go down the sides of the heater, under the firebox, through the bench, back under firebox, and enter the chimney at floor level. I had a local welder fashion a bypass, seen in upper left corner – when open the gases go straight into the chimney to establish draft from a cold start. I installed a secondary layer of 1 1/4″ firebrick splits on the back and side walls of the firebox. As they wear out over time, they can be chipped out and replaced without doing any damage to the full size firebrick that make up the structure of the core. It’s like, um, replaceability. There are four cleanouts, two in the bench at the front, and two on the side of the heater. I made custom notched firebrick plugs for each cleanout, and then Bill mounted a simple, removable pine board in the cob facing, which may or may not end up being painted/decorated.
OK, cob facing. Sand and clay, no straw. We didn’t use straw to keep the mix as dense as possible for best heat transfer and storage. It meant that it went REAL SLOW. Even a dry mix would start to slump after about 6 inches. So Bill did a lot of cob work in the evening after our afternoon layer had started to set up, in between stories told to his granddaughter. I went with 3″ thick facing on the back and sides for a quicker heat transfer, and 4″ thick in the front for a better door anchor. The door…I put a mess of pole barn nails, screws, and then a wire network out the sides, top & bottom. This is all embedded in the cob for stability. Strong like a janky spaceship. Pasted a thick layer of cardboard all the way around for an expansion joint between core and facing. Used two layers up near the top in higher heat areas.
We put a scratch coat of plaster with chopped straw to even things out, and to set tile (left over from the floor many years ago) on the heater top. At the last minute, I stuck a stainless steel pipe that my welder had laying around through the castable refractory capping slabs for overfire air combustion. Albie tells me the most efficient masonry heater burns now days are being done with secondary air combustion introduced into the firebox, 2/3 of the way up. My version is not in the least scientific, but it does make the fire rip when it’s in full burn. The rock on the heater top regulates flow into the pipe.
Final plaster with kaolin clay, mason’s sand, finely chopped straw, mortar pigment (“sand” color), and wheat paste. It burns clean, holds heat for up to 24 hours, and kicks out a lot of warmth for its relatively small size.
All in it cost about $1200 in materials. (Firebrick, gas for my pickup, saw rental, discount door, flue tile, firebrick mortar and castable refractory cement…little things add up in a hurry). Labor is a factor here, with the time needed to do the cob facing. I had visions of a $500 heater in materials, but that is for another time.
At a certain point, I started dreaming of a totally hand-formed heater, bags of fireclay mixed with sand for the core, slowly shaped up organically, a cob facing, no power tools, no metal, a simple clay door… If anyone puts one together, let me know. I’m going back to the woods.