Archive for the ‘rocket mass heaters’ Category

Well, the updates continue to be slow to come and sparse on detail but that’s because we are still working away. I had hoped we’d be in by now, with only floors and ceiling to complete before we could start moving stuff over. Who knew floors and ceiling would be so challenging in round(ish) rooms? We were going to go with a natural feel to the floors, a lime finish, but changed our minds at last minute. Partly for the convenience of cleaning and in part for the extra buffer from the cold we decided on a dark laminate flooring (I know, I know- not very ‘natural’ but gorgeous) and it turns out I suck at cutting laminate floor boards, much as I love the power tools. 

Our ceiling took us a while to decide on. All of the aesthetically pleasing options seemed too rich for my blood and the cheaper options were not at all appealing. We finally settled on buying 3/8 inch plywood, cutting it down into ‘planks’ and staining them a cedar colour. Very pretty effect and well within budget. Since I was ‘off’ floors and able to finish insulating the place, I decided to try my hand at ceilings. I wasn’t particularly discouraged the first couple of times I had to take down an entire day’s work and replace it. I’m used to the whole trial and error thing at this point in the game and I’m nothing if not tenacious. But having viewed my latest efforts Shane demoted reassigned me to chopping firewood. 
Fine. I’m good with an axe after years of camping and I don’t mind chopping wood all day. Not as fond of the hatchet but I’m mixing up the bigger logs and smaller kindling to give my shoulders a break. But it does mean that the entire burden of finishing the house is on Shane now, and that’s slowed us down a fair bit considering he does work full-time. Nonetheless, he’s making good progress and with any luck we’ll be in some time in December. I hope. 

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The pocket rocket is a brilliant little invention that Ianto Evans and Larry Jacobs came up with some time in the late seventies, early eighties. (Yes, I did mention to Ianto that he might have thought of copyrighting that name before another, ahem, ‘invention’ made use of it. Hindsight, eh?) We built one for use in our sauna last year, to try out both earthbag building and rocket stoves at the same time. We went out in January to test how it would stand up to colder temperatures and within under ten minutes, we had raised the temperature from -15 C to +35 C, a 50 degree difference!

It requires only a few easily scavenged materials and is a great ‘starter project’. You’ll need a 30 or 55 gallon drum- one with a detachable clamp-on lid is great for a pocket rocket. And a couple of pieces of pipe- one for the feed tube and one for the chimney. That’s it. A little mortar for around the pipe and you’re ready to roll.

Start by burning off any paint on the barrel. We just stuck ours in our firepit and let it go for a while. While you’re waiting for the drum, cut two holes in the lid- one to fit each of the pipes. (Note: if you want to use the top of your stove for heating water, you’ll need to position those holes with enough room for a kettle or pot.) We didn’t cut our holes to the exact size of the pipe- we cut them slightly smaller and then cut tabs to fold up along the pipe for a nice snug fit.

When your barrel has cooled, dust off any remaining paint. Place your rocket stove somewhere away from anything flammable. (Seriously- this thing heats up like crazy!) Put the lid back onto the barrel and position your feed tube. It should be a few inches from the bottom of the barrel. Place your chimney in the other hole. The chimney (exhaust) only needs to go into the barrel a bit, several inches should do you.

The rocket stove prefers small diameter, straight wood. Gather some up and test drive! It’ll sound like a rocket when it fires up- that’s the draw. If it’s roaring when it starts- you’re good. Wait until it cools a bit and then mortar around the pipes. If you’re not getting the draw you want, fiddle with the feed tube a bit until you get it to just the right height. It may take a bit of patience, but this is a stove you can build in a matter of hours, so it’s worth playing around with to get just right.

Have fun- and let us know how it works out for you!

NOTE: If you want to preserve some of this heat, you could easily cob around the lower half or two thirds of the barrel. Otherwise, be prepared for some incredible radiant heat!

DISCLAIMER: This isn’t something you want to be building in your traditional home, as it would be a fire hazard.

Barrel for the rocket stove

top of barrel, with holes for connecting pipe

basic pocket rocket

pocket rocket fired up

A couple of rocket stove mock-ups

A basic pocket rocket used for interior heat

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We intend to go entirely off-grid. I can’t say exactly when we’ll hit that goal, or what the final system will look like quite yet. Redundancy is important to us so that if a component fails or is down for maintenance it’s not an entirely dire situation. So is efficiency. Ideally, we want the greatest return for the least input- particularly where fuel is concerned. We’re confident that the rocket mass heater we’re building to heat our main living space meets this criteria.

A rocket mass heater burns (wood) fuel extremely efficiently. Seriously efficiently– which is important to us for several reasons not the least of which is that we live on the prairie. There are lots of systems that make this claim but I have never seen anything like the rocket stove. When we were in Oregon, one of our projects was a rocket water heater. When we fired up the system to test it we were encouraged to go around to the exterior of the building and put our faces close to the exhaust. (I know, I know- apparently I’ll do anything for a lentil burger.) I was utterly amazed when instead of a face full of smoke, I was greeted by a cool steam. The wood was burning so efficiently, and the system using all of the heat, that there was nothing but a light steam by the time it reached the outdoors. This is the promise of a rocket mass heater.

That’s the other very important feature of the rocket mass heater- efficient use of heat. When you think of a traditional forced air system, or even a regular wood burning stove, it’s clear to see that a lot of heat is wasted. The mass heater, on the other hand, stores the heat for slow release in easy to build, dirt cheap furniture. Excuse the bad pun. The heat travels down a course built into the furniture (in our case, a combination couch/day bed) transferring its heat to the cob that encases it and slowly releasing it. Essentially, the chimney is inside of the furniture exiting only when it has had a sufficient run to use up the heat. For example, a standard 6” system would have a run of about 30’ and be enclosed in about 3 tons of material.

When you hear talk of rocket mass heaters, you’ll hear frequent mention of the combustion unit and the thermal battery. The combustion unit is roughly J-shaped, and is made up of the feed tube, the burn tunnel, and the heat riser. Measured precisely, and with good mortar and insulation, the combustion unit burns fuel very efficiently and draws well. The thermal battery, as mentioned, is in the furniture itself (or the floor, though it’s not a recommended first time project) in which the heat is stored.

It’s important not just to get the measurement of the combustion unit right, but to carefully consider the run. You don’t want to place the pipes too low into the furniture (or maybe you do, for a much slower bleed and perhaps warming the floor in front of the bench) but you don’t want to go to high and risk a burning hot surface. About 6” from the top of your bench is recommended for a nicely toasted bum. Your initial run will be the warmest, with every length doubled back running slightly cooler- assuming that you’re doubling your run (we may be tripling ours).

You’ll also want to insulate underneath the combustion unit and behind your bench (couch, daybed…) if it sits against a wall. No sense bleeding good heat into the wall. Vermiculite (industrial, not agricultural), perlite, or pumice are all good materials. Use your imagination but avoid anything that may off gas, like foams.

For all of this you’ll need only the most basic materials. Bricks (which you can reuse or make), clay soil, sand, straw, urbanite or rocks (for heat storage) and a couple of barrels and stove pipe, or metal duct. The size of your barrels will vary between 15 gallons for the feed tube, and 30-55 gallon for the heat exchanger- depending on your specific design. Most, if not all, of your supplies can be found and reused.

If I’ve made it sound complicated- it isn’t, but there is some patience and tinkering required. You can’t (or rather shouldn’t) just throw your system together and encase it in cob. You build the system, and fire it. Check it for leaks, or a weak draw, or any other issues, rework your design and fire it again until you have a leak-free system that draws well and burns efficiently. You’ll know it draws well because it actually sounds like a rocket. I’m sure I’ll eventually tire of the sound when it first catches but I’m still just amazed every time that I hear one start. You’ll also want to decide how much radiant heat you want as that will decide how much of the barrel to leave exposed. Myself, I’d like to boil water for tea on top of the heater, so I’ll need to position the heat riser to within 2” of the barrel to create a hot spot.

Once your design is perfected, you’re ready to encase the entire thing in cob and wait for your new furniture to set. (It’s a good idea to test it once again, before your furniture is rock hard.) If you’re a patient person, you’ll have a mass heater that will last you for years. If you try and rush this, you will regret it- it’s not as easy as throwing out an old couch.

Now, having said that it’s efficient and simple to build- I’m not going to go through the entire process on this blog, nor could I without writing a book-length piece. Pick up the actual book- “Rocket Mass Heaters” by Ianto Evans and Leslie Jackson- it’s well worth it. You can buy it in book stores but for the (small) profit to go directly to the authors, you can order it at http://www.cobcottage.com/products . The book will walk you through the main components of the system, layout, calculations and exact measurements. And, apart from the fact that you won’t be able to build a mass heater based on my brief overview, the book also provides alternative models and adaptations, including a rocket hot tub, a Guatemalan cook stove, and an ingenious little coffee rocket.

As a prelude to building a mass heater, try your hand at a pocket rocket- a very simple rocket stove. It is really easy to build and throws an amazing amount of heat, but most importantly it will get you started, build your confidence and have you well on your way of being as hooked on these wonderful heating systems as we are! I’ll provide full details and pictures so that you can build your own pocket rocket in my next blog.

The combustion unit of the water heater

The combustion unit of a mass heater

Note the clean-out

Super cozy rocket mass heater, Cob Cottage, OR

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It seems we’re always racing time, or the weather, or some other factor completely outside of our sphere of influence. It’s a typical October in Alberta, which means we’ve had our first (second and third) snowfall. It hasn’t snowed in a few days now but we haven’t hit above freezing temperatures either and the acreage looks like a veritable winter wonderland. It’s beautiful really, but not entirely conducive to outdoor work- at least not until we’ve more fully acclimatized.

We’ve just about finished plastering the buildings for winter. A few half decent days and we should be done. And we need to get some above freezing weather (forecast for next week) to finish the last row of bags at the front entrance. Other than that, we need to finish temporarily roofing the structures and fit the windows so that we can work indoors through the winter.

We have plans for a rocket mass heater in the living room, as well as a greenhouse sunspace, and have cabinets to build, a bathtub to form, and pipes for greywater reuse to lay out. We’ll also need a part wall in the kitchen. I’m sure there’s more that I’m forgetting. One of these days I’ll get around to writing out a handy ‘to-do’ list but in the meantime…

We also have plenty of outdoor work to complete, including moving tons of earth (quite literally) to build up the garden around the kitchen and living room areas. Because of the sheer mass of the buildings, and the materials we’re using (primarily the earth beneath our feet), the zone immediately around the building on the south side will be different than elsewhere on the property and we hope to be able to grow plants that would not otherwise do well on the property. The ‘surround garden’ will also further shelter the building from some of our more extreme temperatures.

Add to which there are the day to day tasks and preparing for winter- clean up (long overdue), preparing the garage and shop for indoor work, reorganizing materials, covering the last of the raised bed gardens, and so on. (And this doesn’t even speak to the commitments that we have off the property…) It could be overwhelming but strangely it’s not. I think I’ve finally found my ground in this pioneer lifestyle and have come to appreciate the work, even the sheer amount of it. Maybe it’s because I can’t think of another time in my life when the work that I was doing felt so right. And maybe it’s partly due to the fact that my body has had time to heal from the abuse heaped upon it during the building season. Either way, I’m feeling good about it.

Section of kitchen still to be plastered

West side view

Southwest view

Southeast view, from front

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this is the site, dug to foundation level with trenching started

We broke ground the second week of March. It’s been, well… It’s been real. Don’t get me wrong- it’s exciting- but digging has been hard going, what with a small hill to move and enough rocks to build yet another hill. We finally hit foundation level last week though, and really that’s not all that long considering there’s just been the two of us, a couple of shovels, and a pickaxe. 

We’re on to trenching, and if digging was a chore before I don’t even know how to describe it now. The ground is ridiculously hard and weather has not been cooperating. We had several days of weather warnings in the last week, with winds ranging from 60 km to 100 km/hr. And snow- plenty of snow. Thankfully it melted fairly quickly but they’re forecasting another 20 cm will fall in the next 24 hours. 

I’m finding some days (like today) a little discouraging. Hard to find the motivation when you can only scrape the earth bit by bit into a wheelbarrow. It makes for a long day when the progress is so slow. But I remain determined, and committed, so an off day here or there won’t throw me off for long. Shane, in the meantime, is focusing his efforts on our rocket stoves. We’ll require three in total- one for mass heating, one for water heating, and one for cooking. All variations on the basic model that will have to be built and tested prior to the actual build- so he’s got his work cut out for him. When I start to feel badly about all the digging I’m doing, I remind myself I could be stuck with the heating systems which seem- to me- to be a worse assignment. 

So that’s where we’re at. Sorry so long between updates. It’s a busy time. For those of you interested in steadier (albeit short) updates and the opportunity to interact with other natural builders, please see our Facebook page and sign up. The address is http://www.facebook.com/pages/New-Brigden-Alberta/Canadian-Dirtbags/128912733998?ref=mf

A clearer view of the rubble trench

And so digging was delayed for a couple of days...



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I love living in Canada, wouldn’t trade it for anything. Oh I enjoy traveling, for sure, and could spend months on end in Mexico alone but I always look forward to coming home. At least now that we’ve abandoned city life. It does, however, present its share of problems for natural and conventional builders alike- namely climate.

Here on the prairies our temperature ranges from as low as -50 C to as high as +38 C or so. The heat I can handle, and a few well-placed vents and windows with overhangs will go a long way towards keeping a house comfortable on those long summer nights. Cold on the other hand- now that can be a problem. Having said that, a good plan and some common sense go a long way.

Currently, we live in what (by conventional standards) is considered a quite comfortable home. We have three bedrooms, two bathrooms, large kitchen, living and laundry areas, a sunroom, and a full basement with attached garage. There are lots of large windows for light and expansive views. Sounds wonderful, right? Well, in summer it’s not too bad (save for those ridiculously hot days when it’s clear no one was thinking of a cross breeze during design). In winter, it’s an entirely different story.

There are entirely too many windows in this home. The windows on the north and west sides do nothing to contribute to comfort, they are an aesthetic addition. We lose a tremendous amount of heat through our windows in winter, which brings us to heating… Forced air heating has got to be one of the most impractical inventions ever conceived. Not only does it make me sick, gasping for air after a ‘good’ night’s sleep, it’s so temporary it has to run all the time to maintain a steady temperature. And still I’m not warm. Traditional heating is inefficient, unhealthy and irresponsible. Add to which it keeps us tied to the grid, so tied to traditional work to pay for the ‘luxury’.

So what does a natural builder do to combat these issues? Well, for starters, we build small. I’m far from the view that a person can live comfortably in a single room home like some natural builders would suggest- at least not this person. But I do believe a large amount of space is wasted. Our demonstration home will be small relative to traditional housing and maximize the use the space with storage built into the structure itself, underneath and behind furniture, and overhead. Additionally, we will simply have to adjust to the fact that we can no longer house the junk that we’ve accumulated over the years, nor can we afford to continue to collect it. (Stay tuned for my “Lament for Shoe Storage”; I’m a work in progress.)

Secondly, we will orient our building solar south and strategically place our windows. By orienting our building south, we maximize our solar gain. Windows will be expansive on the south side only, with smaller windows to the east, a much smaller window to the west (where the only solar gain would be in the summer, when heat is already at times unbearable), and none on the north side. The main living area, which all of the additional rooms will connect to, will be partitioned to include a small south facing greenhouse. The greenhouse will provide not only additional food, but (because it is double glassed) provide considerable heat (in the form of solar gain) to the living area.

Thirdly, we will build heavy. There’s no sense in planning around solar gain if there’s nothing to absorb the heat. Heavy clay-sand walls and thick earthen floors and plasters absorb heat quite nicely, and are slow to release it. And this is where heat matters most, in the areas that a person has contact with, not the air as it drifts by. I’m reminded of this now, as I sit next to the heating vent and warm air is hitting the side of my body but I don’t dare yet put my feet on the floor.

On the subject of mass, we’ll build “rocket mass heaters” into the design. If you haven’t yet heard of these, see the pictorial below, or get a copy of the book from Ianto Evans if you intend to build your own. They borrow on the efficiency of rocket stoves and take it to the next level. Basically, it is an extremely efficient wood burning ‘stove’ with a long run of venting built right into the (cob) furniture. It requires ridiculously little fuel and (because mass retains heat so nicely) provides an exceedingly cozy sitting area. And, because of the genius design, it burns clean. I don’t blame you if you’re hesitant to believe these claims (I was) but build yourself a very basic rocket stove for all the proof you’ll need.

Finally- we’ll insulate the heck out our building. As our intention is to build as naturally and cheaply as possible- and use recycled materials wherever we can- we’re going with papercrete. The entire building will receive a papercrete plaster about 8” thick, topped with lime. Additionally, the sub-floor will be made of papercrete. (*Note: there are some problems associated with papercrete and mold in humid conditions but we happen to live in a drought area. I wouldn’t suggest papercrete as a sub-floor in damp environments.) The R value of papercrete is cited ~2.5 per inch, dependant on the mix (the higher the paper content, the higher the R value), so at 8” thick will more than provide for our needs.

So that’s the plan for surviving the Canadian winter, and I dare say we’ll do so more comfortably (efficiently and cheaply) than we currently do.

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Barrel for the rocket stove

top of barrel, with holes for connecting pipe

rocket stove inside of dome

inside of dome

lit with Caragana branches


rocket water heater at Cob Cottage

Fuel feed for water heater


New water heater being built at Cob Cottage, OR

rocket water heater


Rocket mass heater, Cob Cottage, OR


very cosy mass heater bench

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