Nice to hear your thoughts on our last post!
Sounds like you are as excited as we are about the option of staying warm without running an unattended fire in the house all night.
After ten years building and testing these heaters, we are pretty confident in what rocket mass heaters can do, but there are a lot of ways to use the same insights in a given situation. Thermal mass heat storage, radiant vs. convective heat: there are many ways to design around the same basic physics.
|Bonny 8" Convection Bench, |
photos courtesy of Calen Kennett,
taken during the filming of
How to Build Rocket Mass Heaters with Ernie and Erica.
One case in point was a 5000-square-foot, 3-family home in northern California. They called us in a few years back when their central heating ducts were moldy from the damp under the house, and they were using 8 cords per year to heat the big place with a fireplace insert and two woodstoves. It was about all they could do to keep the wood shed stocked, and the upstairs bedrooms were still clammy in the damp winter weather.
After putting in a rocket mass heater (the Bonny 8” Convection Bench), their wood use dropped to about 2 cords per year (¼ the previous). They were still using the two woodstoves in the wings whenever they felt like it – just not as often. Thanks to the combination of thermal mass heat storage and constant convective circulation, the upstairs bedrooms are warmer than they had been for years. They are pretty happy, obviously, but that's not the end of the story.
|Bonny 8" Convection Bench,|
showing warm-air vents in bench back.
People who visit their house, lounge on the warm bench, and see the upside-down get fascinated, and want one of their own. In the next two years, we had a number of calls, consultations, and at least two more workshop clients who were inspired by this one stove.
I get excited when I hear about the contagious interest in these heaters. It always feels good to know you're making a difference in people's lives. Our designs can benefit forest health, air quality, fire safety, and even the health of the birds, soil, and water that are damaged by commercial fuel extraction and transportation - but only if they're used, and if the idea spreads. The users have to be satisfied enough to stop using their old heating methods, and to recommend and share these clean heaters with others.
A big part of what makes these heaters contagious is that they do not demand austerity. Unlike getting a smaller car, or turning down the thermostat, rocket mass heaters are a beacon of luxurious hospitality.
Friends with high-stress jobs fall asleep on our bench after dinner. Band practice is better in a rocket-heated garage, where steady temperatures and humidity keep things in tune. In the country, everyone appreciates reducing the firewood chores, better sleep without waking to feed the stove at night, and savings on heating bills. Our people are not going to freeze to death if the power goes out, or they can't get a propane refill during a winter storm.
Rocket mass heaters combine about seven key insights. As an open-source technology, these ideas are freely available for people to learn how they work, pick and choose which aspects to use.
|Woodstove with mass wall: |
The earthen masonry half-wall
beside this woodstove
stores heat: from the stove, and
free sunlight from the windows
(south-facing windows are
to the right, beyond the sink)
- Thermal mass heat storage: If a bench doesn't suit the home, thermal mass can still help provide overnight heat. It might be a huge masonry tower, earthen plasters or "mass walls" collecting woodstove heat or winter sunlight, or even a simple pile of stone or brick behind an existing wood stove. I've seen people in tiny houses or trailers use a bunch of stockpots of water on their woodstove range to hold heat overnight.
- Radiant heat: If you don't like the look of a round, black metal surface, radiant heat can be distributed by elegant tiles, or by changing the angles in existing fireplace to resemble a more efficient Rumford configuration. A heat source that is centrally located, in line of sight of the room(s) needing heat, will heat more evenly and effectively.
- Insulation can be lining the drapes on certain windows, putting a blanket over the attic hatch, or sorting your storage closets to put the fluffiest stuff along outside walls.
- Clean fire, as we described in the previous letter, is good for all kinds of stoves and fireplaces.
We have lately seen several beautiful examples of "Mass Walls," with earthen plaster and mica highlights, or country slate stonework behind the woodstove, or just sand and clay loaded into the cavities of an existing stud-framed wall.
Make sure there is a good footing to support them (floor joists may sag if they're offset too far from load-bearing walls below).
There are a lot of non-combustible, dense materials to choose from, so the mass wall can double as both heat storage and heat shielding for your framed walls or cozy cuddle-spot furnishings. Put the mass wall across from the heat source if it's a fireplace, or build it up between the heat source and any exterior wall that is getting more than its fair share of the heat. (Capturing that heat and reducing the exterior wall temperature will save even more energy.)
Why is heat storage important? By storing the ambient heat longer, using mass instead of air, we can have good ventilation in the home without sending all our heat out the roof vents or chimney. The internal walls can be warmer, and outside walls and ceiling cooler, providing greater comfort while reducing heat loss. We can reduce the actual BTUs needed to stay comfortable overnight, even in poorly-designed homes.
You can use thermal mass storage with any kind of heat, including free solar energy (for passive-solar and direct-solar designs, see www.builditsolar.com), ambient heat from occupants and cooking, or purpose-built heaters and fireplaces.
Smarter use of renewable resources is important not just for home budgeting or winter survival, but for larger global energy issues. Ernie and his dad, like many other fishermen, nature-lovers, and seafood-eaters, break their hearts watching preventable disasters like Fukoshima and Deep Horizons that hurt our coastal communities for generations to come. International politics gets heated quickly when a conflict zone impacts energy security for wealthy nations (the poorer nations presumably just suffer with less belligerent bluster).
Nobody can single-handedly save the world by riding a bicycle or switching to renewable heat. But when we can take care of ourselves and our families while also reducing those bigger problems, it feels good.
|Mediterranean rocket mass heater |
from Chapter 3 of our new book:
built by Adiel Schnior and team,
photo courtesy of Adi Segal.
There is nothing like feeling your body melt on the heated bench, or seeing how little wood it takes, to convince people they want this for themselves. It's much harder to explain in words, or pictures, the attraction of these warm beasties.
One of the biggest objections when people first see the rocket mass heater pictures is,
“How can you stand to look at an old barrel in the front room?”
|Israeli stove with tile |
and ceramic-bangle details
(image courtesy of Adi Segal)
This problem is really a looks versus function issue.
The barrel's job is to be airtight and spread radiant warmth all over the place (and to be affordable and eco-friendly). A smooth, round, weathered-steel cylinder turns out to be a really efficient way to do this, and recycled barrels are cheaply available almost everywhere.
After enjoying the heat from the barrel, who wants to spend a few hundred dollars to replace it with a better, thicker, different, or “prettier” black metal cylinder? The most effective upgrades would really look very similar in the room.
Some folks do go for a custom rolled steel cylinder, or create interesting stuff with reclaimed parts from old cast-iron stoves or other objects. (An upside-down garbage can be disguised as a Greek column, but is that really better-looking than a barrel?)
|Copper over barrel |
(not as good at radiating heat)
We tried a polished-copper cladding on our new Cabin 8” heater, but took it off again after a few months because we missed the radiant heat. (Copper at that temperature is an alarming conductor – too hot to touch, with no warning as you bring your hand closer, yet it doesn't put any heat across the room).
Most often, folks live with the plain black barrel, or add a few decorations to their taste: clay, lime, or stove-enamel paints; bangles; or brassy “lingerie,” while leaving plenty of black metal surface for heat delivery. I just picked out three photos of nicely-decorated barrels to include in the color section of our new book.
|Finished Cabin 8" Rocket Mass Heater |
with brass decoration and exposed barrel
Speaking of our new book:
The Rocket Mass Heater Builder's Guide is on track to come out this June from New Society Publishers. It's full of details that have never been pulled together in one place: like a 10x upgrade to our existing plan sets.
We are releasing a Kickstarterpre-sales campaign in a few days, using this last little bit of winter to hopefully engage people's attention. There will be some nice reward packages and discounts to our early supporters, and the results will affect our game plan for this year's projects.
Please sign up for our mailing list, or for updates on this blog, to get the announcement for the official opening.
Thanks for reading. This book and Kickstarter campaign are big steps for us. We welcome your advice or questions. Please stay in touch.