Though I expect to be in town for quite a while, I gave in to temptation this morning and called about some small country acreages with owner financing. The spot is beautiful, the price pretty high (especially considering development costs), but the seller turned out to be a cool guy very much worth talking with.
He’s into permaculture is a longtime builder of woodstoves.
He was all excited about this: the rocket stove mass heater. (Here’s a Wikipedia article, which contains some reality checks.)
It’s a recent derivation from the rocket cook stove — though the fundamental technology has probably been around for thousands of years.
Heat your house with a $20 homemade stove from scrounged parts and wood that, in other places, would qualify only as kindling? Very interesting …
Anybody have any personal experience?
That is incredibly fascinating! I might have to find a place to build an earthship, just so I can build one of the stoves into it.
That is neat!
No personal experience, I’ve never heard of it before. It looks like it’s surrounded by – what? – stucco?
In the Wikipedia article on the Rocket Stove, it looke like it can be used outside. I wonder how heavy it is, and if it can be taken to a campsite.
I’ll hafta check all that stuff out more thoroughly. The only thing I am unsure of is how to you get it burning from “cold” without filling the house with smoke?
Bookmarked the rocket stove site. I’d been planning on a masonry woodstove, but that one would fit my tiny house better. Now, to find or design an alteration that would let me bake stuff in it, too!
I don’t understand that either. The article said “exhaust is nearly pure steam and CO2 (a little smoke at the beginning)”. So how much is “a little”? I couldn’t find the answer.
Youtube is full of videos. I’ve only seen small scale ones myself. The key to keeping the smoke from coming back on you seems to be that the chimney needs to have enough rise to it to get a draw started.
wood-gas stoves can also be alot of fun to experiment with.
Loompanics books [R.I.P.] had a book on these years ago.
Interesting. I’ve long been familiar with small rocket cookstoves (RC). But this is pretty different.
In an RC, the fire is started in/under the combustion chamber with the exhaust venting out a conventional vertical chimney. With this, once the fire has gotten going and heated the secondary combustion chamber (that vertical barrel) draw should take care of keeping the exhaust going the right way. But I don’t see what keeps the house from filling with smoke before thermosiphoning gets going. I wish I could see the videos; maybe they make that clear.
The secondary combustion chamber is not new by any means. That’s what the upper barrel in a dual barrel stove set up is for. But putting the thermal mass INSIDE is new to me. For faster heat to warm up the room, this set up may be better. For even, warm-but not scorching heat, external thermal mass seems best. I think I’d add a layer over brick on the top of the barrel for the best of both worlds.
He says creosote build up isn’t a problem. Again, I’d like to see the vids. I would expect that barrel to shed heat quickly and grow a layer of creosote fairly fast. But since it IS a secondary combustion chamber, a creosote fire there shouldn’t be disastrous. I’d certainly want the horizontal exhaust section to be damned fire resistant, though: ceramic flue pipe (which would also add thermal storage mass) rather than steel pipe/liner. That “portable” stove pictured with what looks like flexible dryer vent hose going to a sealed fireplace is scary.
Properly constructed, this looks like a good thing. For permanent home installation (all my rocket stoves were small, portable cookstoves), I’d add a horizontal fuel door so I could slide in larger pieces of wood to last through the night: RCs burn the small stuff FAST, and you’d need to reload it almost constantly in a climate like my present location. Fast and really hot is great when you’re firing up the grill to make breakfast; not so wonderful if you want to sleep through the night.
Claire, perhaps your readers should look at rocketstoves dot com or get the book “Rocketmass Heaters” by Evans and Jackson. Sorry, I don’t know how to make a link.
The book goes into great detail, and the technology is mature now. One caveat, it is essential to follow the method used in the book for guaranteed results. YouTube has a great many clips that demonstrate the techniques; some good, others more along an experimental line. Also, one may google “rocketmass heater” and find many resources listed.
I’ve used a small one to heat a greenhouse. I gained about 2 months on either side of my normal growing season without a lot of work. The thermal mass of the thing acts just like a masonry heater. It gives up the heat slowly, but takes awhile to get going.
Creosote build-up isn’t normally a problem as, if done properly, the gases burn up in the top of the barrel. Again, it’s important to follow the instructions in the book for best results.
Ellendra, you can use a combination of cookstove and masonry heater: As the exhaust temperature of most woodstoves is way higher than necessary, you can add heat-exchange channels before going into the chimney. It’s like replacing the firebox of an ordinary Masonry heater with a small cookstove. As a masonry heater stretches the heat over many hours, it’s perfectly suitable for tiny houses. Also hot fire => clean fire, just like a rocker stove. Starting the fire with a cold chimney (little draft) is easier when it’s possible to bypass the masonry part. The bypass is also closed to prevent cooling of the storage-mass after the fire died (masonry stoves are fired periodically).
Efficiency is very high. We use something similar in our home in the mountains of southern Germany (1700 sqft, less than 1.5 cords of pine per year for heating & warm water, winter temp. down to below 0°F, due to well insulated home). Cookstoves can easily be fired with scrap wood like inch-thick twigs. We get all our wood for free, but the stove & chimney were waaaay more expensive than 20$ 🙂
Thanks, guys. I wasn’t expecting this much personal experience or technical insight. Very helpful. Don, FWIW, I’ve got the Evans/Jackson book coming from the library and will probably come back and link to it in a post once I’ve had a look for myself.
Before you take on developing a new home take a look at all the new g#ment regs – like the 22 page “energy” form.
CO. It only takes a few minutes of incomplete combustion and every breathing thing in the room is dead. Dogs can’t detect CO any better than humans; some reports claim dogs are even more susceptible than humans to CO poisoning, injury, and death.
Risk is probability times consequences. You can do things to reduce the probability, like buying and maintaining a CO detector. Or you can drive the probability to nearly zero by sticking with well engineered and properly maintained wood stoves, at the price of sacrificing some efficiency (more wood).
The consequences range from serious neurological injury to death.
You get to decide how much additional risk you’ll accept to save some wood.
I’ve not used one myself,or even seen one, but briefly corresponded with someone who did-the outdoor one(for cooking) worked fine, the indoor version not so(smoke backing up into the house). The outdoor one cost little or nothing to build, but, in looking at it, I’d guess it has a short running life. Maybe start out with the outdoor cooker, and see how that works. I agree with -S concerning using one for home heating.
I would want plenty of research and investegation before I actually built one of these. Most any heating system, if it malfunctions, can poision you with CO2.
CO2 is heavier than oxygen IIRC. If the stove is designed and built right and is airtight inside the building, and safely vented on the outside, how does the CO2 get into the house? I would think, a fire in the primary combustion chamber would draw air in and not allow a column of CO2 to build up and trickle out on to the floor. Once the primary combustion is done, then I believe the production of CO2 would cease as well.
I would want the external vent to be far enough away from the building to prevent expelled CO2 from coming back in. I wouldn’t want rising steam or the small amount of smoke rising back into the house either.
If you design the airflow right, the draft shouldn’t let more than just a small puff or two of initial smoke back into the house. Probably not worse than snuffing a few candles or oil lamps. I’ve worked with some stoves that the positive draft made it difficult to keep a match going because the wind would suck the flame out.
Claire, so Paul Wheaton is the seller of the property? He’s a very interesting guy!! Love the rocket stove concept he promotes, and his hugelkultur gardening method is something worth trying.
Here’s a link to the book by jackson and evans another commenter mentioned — http://www.amazon.com/gp/product/0966373839/ref=oh_details_o05_s01_i00
Oh, and to the person concerned about the CO emissions, the book linked above instructs to vent the emissions outside via a small vent pipe at the end of the loop, rather than into the room. I think that’s the way to go; I was concerned about that, too!
karla — Not Paul Wheaton. 🙂 But thanks for the book link and I’ll look up hugelkultur.
Here’s the same book, linked via my Amazon vendor account for anyone who’d like to buy it and send a bit of the purchase price my way:
Rocket Mass Heaters: Superefficient Woodstoves YOU Can Build
Carl-Bear, you raise some good points. I’d say that the rocket stove is the best of both worlds, providing immediate heat AND lasting heat – the barrel conducts immediate heat and the thermal mass bench holds it for a long time; so you’d build a fire and get quick heat, then stop stoking it and let the thermal mass keep the room/house warm for hours. Theoretically you might make one smallish fire first thing in the morning and let the mass provide heat during the day, then make a larger-ish one in the evening and let the mass continue heating during the night.
[ok, I think three posts are enough… 🙂 ]
Putting a vent pipe to the outside is easy. Making sure the CO goes where you want it is hard.
Wet wood, bad winds, marginal design, a critter who decides to make a home in the vent pipe, the list of things that can cause incomplete combustion and production of CO is long. The list of results is short: death.
About a million people a year die from CO. Many are very poor people, trying to heat their homes with as little fuel as possible. They’ve generally been doing it for years without a problem, but it only takes one event to turn super-efficient heating into tragedy.
People get CO poisoned from fireplaces. It’s relatively rare, but it happens. Fireplaces are relatively large opening, highly vented, with little to limit combustion and produce CO. But it happens from time to time. A heater designed to burn low and slow is at much greater risk for CO.
The Wiki entry Claire linked includes this statement:
“No rocket mass stove or stove design has ever been safety certified by the UL.”
UL is not a government agency, it is a free market firm that has been helping producers and consumers be safe for over 100 years. UL does certify furnaces, boilers, space heaters, and related products. The fact that they don’t do rocket stoves doesn’t prove they aren’t safe – but it does mean that you are on your own.
Mark Twain, speaking about German fireplaces. The stoves are not exactly alike, but in both you burn wood quickly and briefly, and then close the flue and allow the heat to radiate all day. Both burn efficiently and store the heat in a mass of masonry or cob or earth for steady release.
There have been several articles about Masonry Heaters in BWH over the years.
Some of the rocket mass heater designs use outside air (plenty of youtube examples) , which should be another huge efficiency improvement. Any fire drawing inside air to support combustion needs to have enough draft (from an open window or cracks in the insulation) to continue to support combustion. Would you rather have all your warmed air (and inside humidity) used to support combustion and suck in freezing cold dry air through a cracked window, or would it be better to just use outside air that we didn’t just squander BTUs to bring up to room temperature first?
Zero personal experience with the “mass” type stove – maybe some day – but the outside air for inside combustion thing works, and works well.
I took a while and looked at the design and there were two issues that came to mind. First the design will cause air filtration to take place via all the window frames and door frames not to mention any other areas where outside air can creep in like dryer vents, hot water vents etc. in the home. Don’t think this will happen? Then check your home for air filtration. So while the room with the stove will be ok, the other rooms will get cold as air is sucked into the house through cracks around door and windows. The second issue is the exhaust. No matter how hot the stove burns there will be exhaust gas (CO2 etc.). So along with the first issue there is a risk of the gases being drawn back into the house via cracks in window and door frames. These issues could be why they are not UL approved.