It was a mostly uneventful day … as it is dreary and cold and we’ve indoors almost all day … until …
Andreea came back from feeding the chickens dinner with a chicken having difficulty breathing … wheezing (kind of like I do when I get asthma). We did a quick search and came up inconclusive … there were no other symptoms indicating severe or flock threatening illness … but Andreea displayed surprising clarity and took him to our neighbors prepared for a butchering. She came back shortly and was told that it may go away – especially since there we no other signs of illness. Meanwhile I continued to search around and found that it may be as simple as something stuck in its throat (the sack thingy where they store food) … so we poured some oil down its throat (Andreea opened its beak and I poured oil from a spoon) … it was fairly cooperative and Andreea massaged it a bit … and now its back in the barn … we’ll see tomorrow morning how he is.
Another first 🙂
All of our new books have arrived and I am again exploring diverse realms of construction looking to formulate a path towards building our house 🙂
Yesterday we finally got word that the package my sister sent from the USA arrived in Cluj and was waiting for us to come pick it up following a quick customs check. So we decided, after waking up to another dreary day to head out to the city.
The drive to the city was fairytale beautiful – everything is covered in white – still just frost no snow …. but oh so beautiful and delicate.
We picked up the box and went through another short shopping spree. This time the main theme was collecting the things Andreea would need for furnish couches for us. This included fabrics which we will fill with straw to make home-made mattresses, simple fleece blankets to cover the mattresses and and make pillow covers, 6 large pillows, 4 small pillows, buttons and a few other small sewing thingys. So now we have this huge pile of a couch-kit in the living room 🙂
We got Andreea a pair of decent non-work winter shoes and a pair of padded boots for me (the existing boots are not enough for my feet in the freezing temperatures we’ve been experiencing).
We purchased a small pine tree which will be our Christmas tree for the coming years. We are thrilled to have started a healthy (and reversed) process where a tree grows with us until it is planted outside instead of getting and throwing out a tree every year.
We also stopped on the way back and filled four large containers – two with diesel (which we use for lighting our stoves) and two with refined gasoline which runs the chainsaw.
I looked at the car as it was packed full again – this time with mostly fluffy things and I laughed. Every time we come back from the city the car is packed … and every time with a funny mixture of things … and every time I think I’ve seen it all … and then the next visit to the city we come up with another weird combination 🙂
We got a glimpse of the sun in the city (haven’t seen it in almost a week) and the sky are now crystal clear – we are hoping to be blessed with a sunny work day tomorrow 🙂
And finally, we made a stop at neighbors in the village (we brought them grapes from the city market) and we got an offer to buy a pregnant goat for a really good price … it just keeps getting better and better and funnier and funnier 🙂
I believe and have passionately shared my belief that hemp-lime construction is one of the best methods of construction available today (at least in the Romanian climate in which we live). We were planning to build with hemp-lime and our architect designed a magnificent house for us – unfortunately we could not afford to build the house so the project stopped and we are living in the slightly renovated traditional Romanian house on our property.
Building with Hemp was going to be an uphill effort. It was difficult to source materials (we finally found some hemp in neighboring Hungary) and natural hydraulic lime (NHL) is also a rarity here (we found it imported from Italy and Germany). It also seems we would have had quite a challenge mixing the hemp-lime mortar since the best suited tool (pan mixers) are not to be found here. We also had a relatively short window-of-opportunity to build since hemp-lime needs to set (~8 weeks) before the first frost appears – and it arrives early here. So despite our passion and investment in hemp we can say in retrospect that there were many cues pointing us away from it.
When we realized that there wasn’t enough money to build the designed house we started looking at ways to scale down and simplify the house so that we could build it. One of the things we explored were the foundations. Though we had relatively cheap foundations they were still a major expense in the project.
Our house is to be built on a gentle south-facing slope and the plan was to excavate so that the back of the house the excavation was about 1 meter deep. Then we would fill the entire surface with rocks – starting with large rocks (~40cm) and then adding layers of smaller and smaller rocks until we arrive at gravel and sand. On top of that there would be a concrete slab which we preferred to avoid but was required due to the green-roof planned for the house.
With these foundations planned and in mind I first came (about a month or two ago) across two new (to me) themes: rammed-tire construction & underground houses.
Rammed tires is a method of construction where used car-tires (abundantly available is modern garbage) are packed full of dirt and stacked to create a thick monolithic wall that is its own foundations. These need to be built on undisturbed soil and no additional foundations are required. Inside they are finished with earth.
Underground houses (though they may conjure up uninviting images of war shelters) is an approach to building houses that are to some degree (many options here) surrounded by earth. Though there are numerous advantages to this the one that stands out in my mind (as we are living in a small and inefficient house that consumes loads of firewood and the work involved in it) is energy efficiency. Regardless of how you deal with the house fabric (insulation, thermal mass, etc.) when you build a house above ground and its freezing outside then you need to deal with subzero-temperatures surrounding the fabric of the house. When you build a house underground and its freezing outside then you are dealing with a relatively warmer (~10 degrees Celsius) and steady (a couple of days ago I witnessed an almost 20 degree Celsius shift in 4 or 5 hours!) surrounding. In the summer when its hot outside the earth is relatively cool so that works for you too.
So, with that in mind, I’d like to qualify my initial statement in that hemp-lime construction is one of the best methods of construction available today IF YOU ARE BUILDING ABOVE GROUND.
You can’t get far reading about rammed tires without coming across Eartships. An Earthship is a concept developed (if I am not mistaken – way back in the 70’s) by Michael Reynolds – an American architect. His vision is to create an autonomous house generating its own electricity (solar/wind) and water (rain run-off collected from the roof) all built with waste materials that mankind has generated in abundance (tires, beer-cans, wine bottles, etc.).
Ironically my first (and still leading) impression is that it is an impressive vision (amazingly elaborate and thorough) but also one that is anchored in the indulgent and abundant USA mentality (a recurring symptom in most of the “green” construction methods I have come across). Though Earthships are designed to be owner built they are still very expensive and a far cry from becoming something anyone on the planet can afford to live in.
We could not afford to build an Earthship based on the template described by Michal Reynolds and we are very well off compared to the general population of Romanian villages. So bringing Earthships into our context is quite a challenge.
Gradual Self Build
There are numerous benefits to Earthship construction compared to hemp-lime construction and though I will mention some of them there is one that outshines all of the others.
Earthships are designed to be owner built and indeed my searching and reading online seems to indicate that Earthship is one of the most popular self-build techniques for non-professional builders.
But in addition to being suitable for owner-built houses, Earthships can be built gradually. With relatively low costs we can start next year to pound tires that will make up the shell of our house. It may 2 or 3 years (unless we get help) but we can start and as we do that we can continue to develop our income stream and as funds become available invest more and more in the construction. Given that we have a temporary house to live in there is no need to wait, no rush and no pressure at all.
Earthship – Hemp Comparison
Beyond self build there are numerous points of comparison I’d like to make a note of in comparing hemp-lime build to an Earthship-like build. It should be said that what follows are things that matter to us including choices we may make that are not directly true to the core Earthship concept.
|Foundations||Like all natural fiber based walls hemp needs to be lifted above ground level so that it does not come in contact with water that may drain past the building. In our case the green roof required a foundation that could carry and distribute the load of a roof structure, earth, plants and snow.||No foundation is required. The walls themselves are a foundational structure. The tires, when rammed with earth way over 120kg each (they have to be packed in place because they cannot be moved). In addition the tire walls are either completely immersed or bermed with earth which adds additional support (and load on the walls!).|
|Floors||Both building systems can incorporate a variety of floor systems. In both cases, in our climate, there needs to be good thermal insulation (our floors can get to be very cold) and good vapor barriers|
|Walls||Hemp-lime is a non-structural material which means that it is not load bearing. Therefore hemp-lime walls are an infill for wood framing (usually either stick framing or post and beam). There is also need for shuttering (during construction) into which the hemp-lime mortar is cast.||Used tires pile up as garbage almost everywhere in the world – so besides the effort of finding it, sorting through it and transporting the tires to your build site there are no additional costs. It’s as simple as laying them on the ground and then the (very) laborious of pounding them with dirt. As we are not in a rush … we don’t mind taking the time to pound tires.|
|Finishing||Hemp-lime walls are porous and therefore breathable walls so they require a breathable finishing (usually lime-based). On the outside, regardless of finishing, the walls need to be protected with generous eaves.||On the inside tire walls are finished using natural earth finishes they I am assuming that lime can be used as well. This finishing is actually more critical in tire walls because the wall itself is not porous or breathable – so the finishing layer needs to be (for humidity responsiveness). The finishing is a pretty thick layers because first the gaps between the tires need to be filled to achieve a smooth surface – and only then can actual finishing layers be added. As for the outside there is no finishing issue since the walls are either buried or bermed (there is however an insulation issue – see below)|
|Doors||Our hemp house had quite a few doors designed into it. In that sense it was a typical house.||The original Earthships were, except of course for the entry to the house, without internal doors. They have evolved to the point where more elaborate internal design can lead to doors – so I’d say it’s pretty much the same as a regular house (although there is the option to build with much less doors.)|
|Windows||Windows in an above ground house are a pain. They are expensive (if you want good windows). They need to be installed with careful flashing to avoid leaks of water into the house. They need to be constructed and installed with precision so that they are also air-tight. In a do-it-yourself build they can be quite troublesome.||Earthships have no side windows – all the glass is in the front wall which is all glass – it is a relatively expensive element that requires basic wood framing, double-pane glass and very good flashing. The more modern Earthships actually have two glass walls – one is the outer wall which delineates the greenhouse and corridor to rooms; the other is the internal wall which encloses the rooms which is also mostly glass because we want as much sunlight to penetrate into the rooms. I have a feeling that the Earthship is somewhat simpler in this sense then a regular house – though I think the costs maybe similar if not higher.
Earthships also incorporate skylights primarily as a ventilation but also as a light source. This is something that can be self-built so the expense can potentially be somewhat reduced compared to ready made skylights.
|Insulation||Hemp walls need no insulation – they behave wonderfully both in terms of thermal mass and insulation. They do, as mentioned above, need to protected from moisture on the outside – wet walls are not good insulators.||Originally Earthships were built without insulation under the working assumption that they should interact with the earth itself. The modern evolution of Earthships in cold climates (where the earth, though warmer then the air, is still colder then a comfortable living temperature and could therefore suck heat out of the house) include insulation – usually rigid foam insulation (not very ecological) that is installed at a distance of about 1 meter from the wall itself (the space between the insulation is filled with earth).|
|Roof||Hemp homes can be built with almost any roof system. We were planning to build a green roof. Insulation is required and again can take on many forms.||Standard Earthship roofs are designed with a primary function (besides shelter of course) of rainwater harvesting. Here too insulation is a must and can take on numerous forms though standard Earthships use rigid foam insulation. We are currently leaning toward a green roof. This will deserve a dedicated post so stay tuned 🙂|
|Space Heating||Hemp homes can be very energy efficient if they are built properly which includes: airtightness, ventilation, passive solar, etc. But my intuition tells me that they still require heating which is can be a very challenging and complicated and expensive issue. Still they are above ground houses and need to cope with the dynamics outside environment (though the hemp walls, being constantly dry, tend to this very well compared to other wall systems).||Earthship heating requirements are probably much lower even then that of Hemp:
We are continuing to study and investigate Earthships and how they can apply to us. It feels promising.
We have been blessed with a temporary house in which we can live yet it is not a house which can become a house that supports and embraces us. This house is a wonderful shelter which can make building our new house a pleasant and healthy process.
The thought that we can begin a building process next year from mostly salvaged materials and then gradually move on with construction as work progresses and more money becomes available … and maybe move into a wonderful and pleasant house in 3 or 4 years is … joyful!
This is what our world looks like this morning. Today is the best visibility we’ve had in 4 days!
3 days of freezing fog … no glimpse of sky or sun … today was better visibility … I could vaguely see the line of the hill.
I’ve been mostly indoors reading, writing, eating, drinking. When it’s this cold, just keeping the house warm is an ongoing task.
It’s beautiful outside – everything is … not blanketed (there hasn’t been snow yet … probably will be this week) … but outlined with white … all ice that has formed and accumulated. It’s such a new palette for me, especially being so close to it … living in it instead of visiting it.
The freezing cold is an issue if I want to go out and do some work. If there is sunshine then there is a 4 or 5 hour window of work. If there isn’t then there are maybe 2 or 3 hours of limited work (wood chopping). I still have quite a bit of woodworking I want to get done … I don’t know how I’ll manage that.
Andreea had an excellent time teaching her first course here in Romania … it should be coming to an end as I write these words. She should be back home tomorrow. Depending on registration she maybe going away mid-December to teach the course again to a group in Brasov and then again in February in Bucharest. I am sooooo proud of her … after so many years of failed attempts to make connections and contribute … finally it’s happening for her, for us.
Folding up here (living room) and moving to the bedroom where I am keeping the fire going. Going to draw another revision of ideas/plans for our future house.
If you are reading this and interested in the technical aspect of Rocket stoves you may want to scroll down to the last part of the post where there is a description of what we actually built. But first, I do will indulge in some personal reflection about rocket stoves.
What is a Rocket Stove?
If you’ve never heard about rocket stoves, though I’ve mentioned them before, this short video is the place to start. This video drew me out of the theoretical reading and into action – anyone can experience the wonder of rocket stoves by recreating what is demonstrated in it:
A rocket stove mass heater is a more elaborate stove built around this concept … it is simple to build, efficiently burns wood – the rocket part (more then most existing stoves) and equally effectively stores and radiates the generated heat – the mass part.
To learn more you may want to:
- Get an introduction at Paul Wheaton’s summary page on rocket stove mass heaters
- Learn to build one with the one and only rocket stove book
- Visit the rocket stove forum (lots of hands on information and helpful people)
- Of course you can and should search the Internet and find plenty of information about them.
However if you want to build one I strongly suggest you get the book – there are a few core details that you have to get right – once you get those down you can play around with it a lot. Though there is plenty of freely available information you will be hard-pressed to find all these core details without the book – at least that’s been my experience.
On to our personal rocket story
A Screeching Halt
Last year, as we were in the process of purchasing the land we currently live on, we were also working closely with our friend and architect on designing our hemp-built house (much more on that in coming posts). He designed a beautiful (and functional!) house, but the more beautiful it got to be the more I began to question its economic feasibility = I didn’t think we would be able to afford to build it. We were really committed to the process and invested much effort and resources in pursuing it (including a visit I have yet to write about to the UK to consult with an architect experienced in hemp construction).
As we were working on our rocket stove it was Andreea who insightfully recognized the point at which our beautiful house came to a screeching halt. We were doing some financial planning and were inquiring with our architect for some input on the house systems. We were sitting in his office discussing options for a house heating system – seeking a rough budget to plug into our calculations (which were already looking grim). He picked up his phone and called a fellow engineer. The conversation resulted in a mind-blowing figure ouf 15,000 euro (half of our target construction budget). We realized that something was not right – we felt that the architect and the engineer lost touch with us and our wishes. Further inquiry into the subject brought the figures down to 7,000 euro – still a lot of money and out of our budget.
Though the project continued to move forward and is still alive though dormant today, from that point on it was winding down. Our wish to have a comfortable and warm home, it seemed, could not be fulfilled within the budget we had.
Preparing for Winter
By the time we moved out it became painfully (at the time) clear that we would not be building a new house this year and that we would probably be spending a few years in the existing traditional Romanian village (cob) house. So, we began a long and ongoing (though definitely coming to a first end) effort to fix it up.
The house has a small hall, a small pantry (we converted into a bathroom) and two rooms. One room has a traditional Romanian wood-stove (the other had nothing). We had lots of plans to do lots of things. Though we did lots of the things, many were not in the plans and most of the plans did not reach execution. Our plans did not include building a rocket stove this year. They did include buying a second stove and a third wood-burning boiler.
Then, we discovered the (above mentioned) 16 brick video, we purchased some firebricks and tried it out … and it worked fantastically. We used it quite a lot for cooking outside.
At one point, just for the fun of it, I even built up around it and simulated a rough rocket stove . I used the parts of an old wood-boiler for the heat riser:
Seeing the horizontal burn for the first time was a magical experience:
And then when I placed a barrel on top, it got really warm really fast:
Then came the two+ weeks of non-stop cooking during which we made loads of winter preservations. We were practically living next to the small rocket stove outside. Then when we moved indoors in the evenings to escape the cold and complete the jar preservations we would light the wood stove. It was painful to see how much wood this stove consumed (and continues to consume) compared to the 16 brick rocket stove outside. Everyday I would have words of awe about the outside rocket stove and complain about the wood-greedy stove inside.
Slowly I gathered the courage to suggest we try building a rocket stove instead of buying another wood-guzzling metal stove. And so it began … from here on it’s going to get a bit technical.
There were a few constraints shaping this project for us:
- Timing – we had already finished putting in wooden floors including a corner of ceramic tiles in each room to house a stove. We did not feel inclined into removing parts of the floor to install a cob-bench (the mass part of the rocket where heat is stored) and we were not keen into working with cob as it takes time and experimentation … and we already had quite a bit on our plate. So we were going to build a stove without thermal mass … making it’s heating efficiency questionable.
- Barrel – This is going to be a recurring theme here at Bhudeva – but finding used/2nd hand anything is much more difficult here in Romania then in the USA, UK or other western countries. This is especially true in villages where everything is used, reused and used again, often beyond the point of efficiency or even safety. A key element in the rocket stove is a metal barrel – and for many weeks (which delayed the project) we couldn’t find one. We finally decided to build a rocket stove with “firebrick chamber with a top metal plate” instead of a barrel (we have since found and purchased one used barrel and have a few more lined up … we will keep them stored for future needs).
- Insulation We also could not locate (at reasonable prices) any of the suggested insulation materials for the internal combustion chamber – we ended up using wood-ashes – they may not offer the same level of insulation and they may settle over time but this is what we had available to us.
- Size – the actual stove – where all the burning takes place is a systemically and purposefully twisted path which, from a certain point early in the path (the horizontal burn chamber) must not become narrower. This is to prevent smoke and dangerous gases from returning into the room – the stove generates a powerful draft and nothing must impeded that flow. The traditional Romanian stove configuration is for a 12cm chimney flue – which is also the size of the chimneys usually built into the walls. Since we did not want to make a new opening in the wall for a chimney we had to adapt to that limitation. This is when rocket stoves designs are suggested for either 15 cm (6 inch) or 20 cm (8 inch). This meant a smaller scale and tighter design and indeed everything was scaled down accordingly. However, in retrospect, given that we built a spacious “brick barrel” as thermal mass – which slows the flow of gases before they exit, I believe we could have gone with a larger dimension in the stove with the limited 12 cm exit flue.
Like most of the good recommendations in the book, building a model of the stove is an important stage of work – and, as recommended, it should be done on a level surface (I tried to cut this corner and it was a waste of time). To that I would add that it should be built somewhere where you can (a) work on it over a period of time; (b) light it; (c) keep it out of the rain or other wet elements. I built our model in a corner of our barn which answered to all of these criteria – and luckily so because we went through quite a few iterations.
I actually used such images to document my progress of the layers (both as I built them up and took them apart) in building the actual stove in place. There were many small details and the images unburdened my memory and were very useful in actual construction. I spread construction sand on the floor to level it. This is the first floor level model (it changed later in the process) … it is designed to raise the rocket off the floor and create ash collection both under the feed chamber (right) and at the exit flue (left).
On top of that came the “floor” of the rocket itself – intentionally adding more depth to the ash collection chambers.
Then of course the burn tunnel
… and off we go – and you can already see the fire climbing up the feed chamber (the feed tunnel is not yet built up):
The model worked OK. The biggest problem, and one that carried over to the actual stove was the fire crawling up the sticks and out of the feed chamber. I now believe that the cause of this was that the feed-chamber and ash-clean-out beneath it were not sealed properly. So the stove instead of sucking air down from the top of the feed chamber was now also sucking air up from below which both lowered the intensity of the down-draft AND provided an alternate up-draft.
Also, if you decide to build something not quite by the book be prepared to take risks – as not everything can be tested (simply) in the model:
- When I built the model I realized that I could not seal the brick chamber nor the top metal plate to the bricks. This meant that we could not assess how effective the generated heat would be contained and radiated from the stove.
- Though the top metal plate (can be used for cooking) heated up rapidly it had a surprise for us in the actual stove. The heat generated by the rocket is so high that the metal (5mm thick) warps … the corners fold out creating stress on the cob that seals the plate to the brick structure beneath it. The cob has cracked numerous times (and let out poisonous gases) and we have had to reseal it (simply applying another coat of clay-slip)… it looks like we have reached the point where it is properly sealed – though only time will tell – we check it regularly.
The following images depict the actual stove in construction. First a simulation of the base layer to get its position in the corner. Next time I would try to leave more space between the rocket and the walls to make it easier to access and install the chimney parts – it was a struggle.
Then a little messier with the clay-sand mortar to keep things in place:
In the middle layer (top image) I installed a metal grail to support the feed chamber and let the ashes fall – I notched (with a grinder masonry disc) three parts of brick to support the grail itself:
Then a metal heat riser (used pipe cut to size at a metals shop in Cluj) went on:
and over that went a piece of sheet-metal tied into a roll and then filled with wood ash
Starting to look like a rocket stove
Here the heat riser is sealed with the clay-sand mortar mix
Here you can see that the heat riser is positioned away from the center of the brick box. One reason is that I assumed that the brick-barrel would behave like a steel barrel does and that the wider space would heat up more/faster then the narrow space – so in this case the wide space facing into the room. The space from the other (left hand side) wall is determined by the location of the ash-pit and exit flue (in the dark area at bottom left of the image). Though I don’t know if this actual works – I preferred to have the gases “linger” in the box rather then get pushed out by making the space near the exit flue narrow.
The almost finished stove with a completed brick chamber (I decided to use refractory cement which has adhesive function for the brick chamber instead of the sand-clay mortar which has no adhesive function it simply keeps the bricks from moving and when fired solidifies into a brick-like material) and metal top still undecided feed chamber, a temporary chimney leading out the door and to the hall, a small pot of water heating up and Andreea checking something out (and providing you with some sense of scale).
We still had smoke-back and fire climbing up the feed chamber … which frustrated me greatly … until Andreea intervened with a bit of feminine surrender and wisdom and suggested we let go of the vertical feed and go with a front feed … which not only worked but demonstrated that the stove had excellent draft with absolutely no smoke-back. Here you can see a fully loaded feed with fire swirling into the stove and absolutely no smoke coming out:
Then Andreea took over the clay plastering. It failed miserable the first few times – the plaster cracked and fell of in chunks.
The third time she (1) added hemp fibers and some acrylic construction glue; (2) wet the bricks thoroughly before applying the plaster; (3) applied it in thin layers and worked it in thoroughly with a wet sponge; (4) continued to moisten and add clay slip as the stove was heated up gradually over the next two days.
The chimney winds through 3 corner bends (poor planning?) so it was a bitch to install … but we now have a great looking and working kind-of-rocket-stove in the bedroom.
Before I talk about the stoves heating performance I’d like to talk about it’s other values – at least those that are important to us.
- Independence – with no past experience in stoves or any of the specific disciplines involved in creating this stove and with no access to people with past experience we managed to build this by ourselves. It can be built fairly quickly (it takes more time to gather materials then to actually build it).
- Efficient and Ecological – when the stove is first fired up some smoke comes out the chimney … but once the heat riser gets hot (very hot) there is no smoke – the stove performs a full and clean burn of the wood. Not only does it fully utilize the energy embodied in the wood (every time you see smoke coming from a chimney imagine waster dollars – all of that is wasted energy) – but it is also ecological since it releases very little pollution (compared to most regular wood stoves). If you were to buy an industrially made central wood heating stove you would pay a heavy premium for “re-gasification” – which is essentially the burning of the gases release when the wood initially burns. With the rocket stove this is an inherent and simply to achieve function (the insulated heat riser gets too temperatures high enough to burn the gases).
- Beautiful – you can shape and mold it and make it your own … which ends up uniquely individual and special.
- Sustained warmth – the thermal mass (in our case the “brick barrel”) contains all of that efficiently generated heat and slowly releases it into the space instead of letting it escape out the chimney.
It works great. Though we purchased a lot of wood we did not have time or do enough to dry it properly. Fortunately we also have a huge pile of junk wood that we collected from all over the place – that wood, after we cut it to size, is very dry and perfect for the stove. In a regular stove it may be desirable for wood to burn “not too fast” because heat is present only when there are flames (once the flames go out the stove and usually the space, unless it is superbly insulated begin to cool). In a rocket stove it is best to have a fast and efficient burn – the heat is stored in the mass and then released. We are currently lighting it with a few batches of dry wood and then some of the partly dry wood in usually larger chunks of wood. If we were to use only dry wood the stove would probably get really hot (too hot to touch) in 2 or 3 hours. As we are currently running it it takes 4 or 5 hours.
It uses much less wood then the regular wood stove (I can’t say how much as we are not yet setup for measuring and comparing. But more importantly it’s effect on the room is very different. Since we don’t have a radiant barrel (only the small top surface radiates heat immediately into the space) it takes time to warm the space – the other wood stove warms the space rather quickly. But once its warm the space will say warm much longer (again I don’t have measurements for comparison) … but we usually feed the stove one last time at around 10pm and at 7am the room is not cold (though not warm). With the regular stove the room cools drastically in an hour or two – once the fire is out the room begins to cool!
The heat has a different quality in the rocket stove room – it’s hard to put in words. It is a softer, deeper and rounder warmth then the regular wood stove.
It can be used for cooking – doing so requires using either very dry wood (which burns fast and releases a lot of heat) or patience (it is generally slower heating then the wood stove where fire almost directly heats the pots.
Until recently we have had to deal with the metal warping problem. It strains the corners of the cob that join the metal plate to the brick box to the point that cracks appeared and smoke/gas escaped into the room. It has been easy to fix – adding a clay slip – but has required constant attention. Time will tell if this is going to be an ongoing issue or one that we have resolved.
I would have been happy to make it bigger (see above mentioned constraint 4) and to get the vertical feed working properly. But we didn’t have time … it as getting too cold in the room and we still had plenty of work to do to prepare for the winter. The result is a stove that needs to be fed every 20 or so minutes … but that is a small inconvenience we are happy to accommodate.
We are very happy with the stove. It came to life just as the room was becoming unbearably cold. Creating it was a hugely empowering experience. We are very much looking forward to experimenting with it more and eventually incorporating simple rocket stoves we can build and maintain with our hand instead of complicated systems that cost many thousands of euros and place us at the mercy of technicians and engineers and companies.
We had plans to build a second rocket with an integrated baking stove and a thermal mass bench (wood framed!) stove to replace the existing wood-stove, but time did not allow for it. Next year 🙂
It’s been a frozen two days, it’s dark outside and cold is beginning to set – a good time to go and light the rocket so the bedroom will be nice and warm 🙂