Bernhard Masterson creates artful natural homes, wood fired ovens, and Rocket Mass Heaters. He teaches a wide range of natural building techniques in hands-on workshops and through Pacific University and Portland Community College. He has built numerous rocket mass heaters and wood fired ovens of various designs since he started sculpting with earth in 2002. As an artist, designer, and devoted maker of things he appreciates the blend of science and beauty that home built heating and baking devices provide. When not helping others pursue their dreams he can be found developing his urban homestead in Portland, Oregon.
Find him online at www.bernhardmasterson.com.
In 2002 I decided to embark on a journey toward a greater connection with the natural world, the seasons and gardening and toward reducing my need for cash. That dream led me to building a snug 450-square-foot strawbale and cob cottage outside Portland, Oregon. The home is heated with the sun and a wonderful Rocket Stove.
With a massive Thermal Battery I don’t come home to a cool house and push a button to turn on the furnace. Instead I come home to a warm house and fire up the Rocket Stove.
Living with a heated bench provides some real treats. Few things are better than coming in out of the cold and sitting on a warm seat. Leaving the next day’s clothes on the bench lets you put them on warm in the morning. Friends linger longer, and rising bread is a snap. There are some downsides of course: those same guests may stay later than you like, and you might have difficulty getting off to bed when your eyelids are heavy and the bench oh so relaxing.
Because I am more involved with the actual heating of the house, I have a greater awareness of the season. Going outside every couple of days to get firewood is an opportunity to appreciate the weather. I try to take a moment each time to feel what it is like outside, even in the midst of a winter storm.
Rocket Stoves are renowned for their efficiency and I’m surely pleased with this one. On cloudy days a 2 to 3 hour burn in the evening uses about a 5-gallon bucket of wood. For regular winter temperatures of 35 to 50°F. This keeps the house at a comfortable 60 to 65°F. The house temperature swings about 5°F, gaining that much with each firing then gradually dropping the same in the next 20-odd hours.
In an earthen house heated with a Rocket Mass Heater, I feel as comfortable in the low 60s as I do in a conventional home in the high 60s. I believe this is because in a cob house heated with a Rocket Stove, walls are much closer to the air temperature than walls in a wooden house heated by a furnace. This is much like radiant floor heating, living in a space with surfaces closer to skin temperature. I radiate less heat to the walls, making me more comfortable.
In designing our stove, we chose to keep the top of the barrel low so we could easily put large pans of water on the top for heating. The 3 gallons of water we heat on our stove each day are used for dishes and bathwater.
Using a 55-gallon drum with a removable clamp-on lid allowed us to build the drum into the wall between the living room and bathroom and still have access to the Heat Riser for cleaning. The radiant heat in both spaces is wonderful. We have, however, discovered a couple drawbacks to the clamp-on lid. One is that the bungholes and rings in the lid limit the space on the stovetop for pans. A second is when we are running the stove really hot, the lid expands and pops up slightly, which is a little startling when it is covered in pans. A lid made from thicker sheet steel may solve these imperfections.
I still think the removable lid is a net gain. To seal the bungholes and lid, I removed the rubber gaskets and replaced them with aluminum foil “ropes.” This worked well and the aluminum did not degrade at all in the first year of stove operation.
Installed in our bench are two 6″-diameter ducts for heat transfer to the thermal mass. Our bench is about 16 feet long. I believe if it were longer we would get more heat out of the exit gases, as flue temperatures range from 170 to 250˚F as gas exits the house.
The ducts in the bench vary from 2 to 4 inches from the surface, which turns out to be an unintentional asset. We can move around from hotter to cooler parts of the bench depending on our comfort. The 2-inch spot may be a little on the thin side and can get quite hot, but it sure reduces the time it takes when we set loaves on the bench to rise.
The first stove I built is in a drafty workshop. When we had strong winds hitting the side of the shop where the flue exits, it tended to backdraft. I solved this problem by opening a window on the windward side of the shop to balance the air pressure inside with that on the upwind side. So for our house stove, I put a fresh-air supply on the same side as the flue to equalize pressure. This has worked well, and I built a sort of heat exchanger with the flue to take the chill off the incoming air (see drawing).
One of my neighbors laughed at our funky stove and the small size of our woodshed as we were building. Now when he comes to visit, his favorite place is on the Rocket bench. And he is envious that we can collect and split our season’s supply of firewood in 2 days because we heat our house with about a cord of wood. Less wood chopping means more time on the bench, and that is always a good thing.
—Bernhard Masterson