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Rocket Stove Water Heater

 
                            
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So I was watching Paul's video on heating water with a rocket stove and he mentions that they recommend not teaching anyone how to heat water because of the danger of blowing yourself or your house up... That intrigued me and had me track down a system our friends at Milkwood Permaculture put together on their farm. Check it out and offer up some feedback on how they designed it and the safety of that system:

-Flickr Photo Series: http://www.flickr.com/photos/cicada/sets/72157613058564419/
-Blog Post and Diagrams: http://www.milkwood.net/content/view/80/1

Cheers,
 
Ernie Wisner
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it will work great in about two hours from lighting simple and well done. lots different then the one folks are talking about that gives instant hot water.

the one pictured needs a simple pressure relief valve. or you can just leave the lid off.
 
                            
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If you read through their blog post they mention that they get hot water in a few minutes of igniting the water heater, using a handful of Acacia twigs. They also mention the water heater has a pressure release valve built into it (most newer models do, I think) so there is no worry for explosion. From my research this system looks to be the most straight-forward and effective that I've seen.
 
Ernie Wisner
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i did read the few min bit but till i see it and the tank size i reserve the right to be skeptical.  my experience with a tank setup that way says different. they might be using something i had not thought of. as i said its a nice design either pressurized or not. I like it much better than many i have seen and done.  new tanks do come with a pressure relief valve i would suggest folks who salvage tanks,  replace that part with a new one often the old are a bit abused.

the best feature of it is no valves that can inadvertently be closed. a definite plus in a community setting.

good design and implementation.  I will be trying to get that design for the next RMH book. tests on the instant hot water are working out well so we may have both designs in the book. /ernie does the happy dance/. keep on experimenting everyone, 
 
                            
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Yeah, they also live in Australia where it's likely that with their climate water is going to heat much faster anyways. How many rocket water heaters have you built or had direct experience with (particularly in cold climates)? I am eager to construct one within in the next year here in zone 5 Michigan.

So you are the Ernie in Paul's videos I assume? I have some questions about the greenhouse you were building with the rocket mass heater in the bed... Will one fire create enough heat to keep the ambient temperature in the bed above, say, 40 degrees Fahrenheit through a night in the middle of a zone 5/6 winter? I'm really intrigued by that design and want to learn more about what sort of advantages it has on season extension.
 
Ernie Wisner
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when the bed is heated fully yes it will. think of the bed like a battery if its fully charged it will do its job till it runs out of charge.

what this means in practical terms is that you will heat the bed till its warm and maintain that warm by firing the stove for a bit each day. the temp drift in your green house will not be very much if you maintain the charge. with a couple additions to how you take care of your green house you can keep the heat up around seventy or so. the bed is radiant so low growing plants inside the zone will not even frost if the bed is outside; there is a limit of about two feet above the uncovered bed.

things like double glazing, an insulated night cover, proper siting and/or  tromb wall can allow you to pick the temp you want inside the structure. I designed the initial green house stove for growing sweet potatoes, ginger and turmeric so the soil temp was critical and had to be maintained at 80 degrees throughout the growing season.

this is probably more info then you wanted hope it helps.
 
paul wheaton
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Somebody was saying they couldn't find my rocket water heater video on these forums, so I thought I would add it:



 
Nick Ritar
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Location: Minnamurra, NSW, Australia
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We have 25 PDC students who are using the rocket stove to heat their hot showers at the moment.

I just asked the room and they estimate it takes 20 minutes of burning to get the first 5 minute hot shower then 5 to 10 minutes of burn time shower after that. They are collecting a small barrow load of sticks each day. The ambient temperature here at the moment is 16 to 25 degrees celcius, but the water is coming from a deep dam that is at around 12c.

We have a Mediteranean to cool temperate climate here with minimums as low as -12c and maximums in summer of +38c we use the shower all year round.

http://milkwood.net/2009/07/12/the_rocket_powered_shower/

Clearly there is more we could do to make it more efficient such as:

  • [li]increasing the size of the heat exchanger - a lot of hot gas escapes from the to[/li]
    [li]raising the storage tank higher than the heat exchanger[/li]
    [li]insulating the heat exchanger[/li]


  • but it works and it works a heck of a lot better than any other wood fired water heater we've tried
     
                            
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    Where did you get the water jacket?
     
    Nick Ritar
    Posts: 19
    Location: Minnamurra, NSW, Australia
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    I bought it second hand locally.. it was a simple wood fired water heater where the fire was built in the centre of the jacket.

    It's basically just a box in a box. the inner box has the fire in it the space between the two boxes is full of water.
     
                                
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    It is a "clam shell" so to speak and its performance while not stellar is indeed sound and positive.

    It is indeed the only type I see as a fit for the rocket design, I have no doubt it performs as described and with minor modifications it is far and beyond other designs IMHO for whatever that is worth.

    Q=u*A*td never changes, you can change the u, the a, the td and in this case they have changed A in  a big way,

    Perfect? Nope, but then again, the third law dictates chaos and a total lack of control lol.

     
    rose macaskie
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          Masonary heaters that are very similar to rocket stoves sometimes have a box of water and ovens in them that get heated up as would an oven in the clay benches that are the thermal mass of the rocket stoves.  The ovens and the box full of water are placed in inbetween the fire box and the expansion chambers otherwise called secondary combustion chambers, between the walls of the fire box and those of the secondary comnbustion chamber for example, so when these4heat up so do the ovens and so does the water.
          The more modern version of the rocket stove mass heaters or masonary stoves, rocket or otherwise, is the  AGA and there is another stove of the type,  that have ovens in them as well as an efficient cooking top and sometimes a tank of water with the ovens, so that they serve to heat water as well as to coook with.
        Google, russian stoves mennenite if you want to see an example of ovens in a mass heater. ,You will find a long article about a Rurssian stove that Carl Oehme stove mason and his prentice Guy Amyot took down and rebuilt, it is the record of an old Canadian russian stove, it is also, for those who are interested in cob, adobe, very interestinfg about how hard and how heat resistent horse manure is as a building material. agri rose macaskie.
     
     
    rose macaskie
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      I have been thinking about rocket stoves, I thought it is not only Paul Wheaton who talks of rocket stoves rather than other mass heaters, it is all permaculturists who talk about rocket stoves and not about the other types of mass heaters. It is a real pity not to read about other masonary stoves it open out the possiblities for making other versions of stoves so that there will be designs that suit everyone. Most of the principles of other mass stoves are the same as those of rocket stoves ecxept  the fires in them are not usually down draft fires, lit from above the fuel but they all burn the smoke in chambers above or to one side of the place the fuel is burning to leave a clean burn that almost does not pollute at all and the fire heats bricks or clay or stones that later generate out the heat keeping the house warm after the fire has gone out.
    It took me  awhile to read about variouse types of stoves but i am glad i did it. I would be even more glad if i had made inroads on actually making a stove as Paul Wheaton has, i want one in my house and i like feeling valid because i have done whatever it is i would like to do, not just hoped to. Rose macaske.
     
    milkwood. kirsten
    Posts: 13
    Location: Milkwood Farm, Mudgee NSW Australia
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    just an update on that rocket stove water heater at the top of this thread, 2.5 years on - still working! http://milkwood.net/2011/08/03/our-rocket-stove-water-heater-2-5-years-on/ and the original post (which has moved since the first link) http://milkwood.net/2009/07/12/the_rocket_powered_shower/

    Anyone wants to come and try it out, you're all most welcome
     
    Dale Hodgins
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    rose macaskie wrote:
      I have been thinking about rocket stoves, I thought it is not only Paul Wheaton who talks of rocket stoves rather than other mass heaters, it is all permaculturists who talk about rocket stoves and not about the other types of mass heaters. It is a real pity not to read about other masonary stoves it open out the possiblities for making other versions of stoves so that there will be designs that suit everyone. Most of the principles of other mass stoves are the same as those of rocket stoves ecxept  the fires in them are not usually down draft fires, lit from above the fuel but they all burn the smoke in chambers above or to one side of the place the fuel is burning to leave a clean burn that almost does not pollute at all and the fire heats bricks or clay or stones that later generate out the heat keeping the house warm after the fire has gone out.
    It took me  awhile to read about variouse types of stoves but i am glad i did it. I would be even more glad if i had made inroads on actually making a stove as Paul Wheaton has, i want one in my house and i like feeling valid because i have done whatever it is i would like to do, not just hoped to. Rose macaske.

     
    Dale Hodgins
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          I get what Rose is saying about the similarities. When I first watched a YouTube video where someone was demonstrating their rocket stove I thought " good someone has had the sense to build a Russian fireplace out of cob and lay it on its side." All the benefits of a masonry heater without the expensive brickwork. When I mentioned the similarity I was quickly rebuked by someone who had a theological attachment to rocket stove's and their magical powers. My own rocket stove will have features of other systems including a large tank of water which is vented to the exterior thus eliminating steam pressure issues. And the exhaust furthest from the feed door will rise to the second floor like one of those Mexican chimneys made from Adobe.

         I'm adding the vertical component to ensure good draft particularly in summer when I'll use the RMH as an air conditioner. I'm also considering placing another R MH about 6 feet from a bank of south facing windows so that it can be used as a trombe wall for solar heat storage during the spring and fall when fuel-burning will be unnecessary. Doesn't matter what we call this hybrid beast. In operation it will be a rocket stove on cold winter nights, a trombe wall when only solar is needed, and an air conditioner/exhaust fan during the hottest part of the year.
     
    Fred Winsol
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    Location: Sierras
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    solar water heating is SO much easier... drainback systems... just a sliver of sun even on a cloudy is all you need.
     
    milkwood. kirsten
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    Location: Milkwood Farm, Mudgee NSW Australia
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    Me again. We just took the Milkwood rocket stove water heater apart after 3 years of service, examined it, and put it back together. working better than ever.

    Some creosote buildup in the heat exchanger and some minor adjustments to be fixed, but all in all, pretty darn happy.

    Photos etc here: http://milkwood.net/2011/10/28/rocket-stove-water-heater-redux/

    Thanks to you all for your ongoing inspiration and knowledge on this subject!
     
                            
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    Ernie Wisner wrote:
    when the bed is heated fully yes it will. think of the bed like a battery if its fully charged it will do its job till it runs out of charge.

    what this means in practical terms is that you will heat the bed till its warm and maintain that warm by firing the stove for a bit each day. the temp drift in your green house will not be very much if you maintain the charge. with a couple additions to how you take care of your green house you can keep the heat up around seventy or so. the bed is radiant so low growing plants inside the zone will not even frost if the bed is outside; there is a limit of about two feet above the uncovered bed.

    things like double glazing, an insulated night cover, proper siting and/or  tromb wall can allow you to pick the temp you want inside the structure. I designed the initial green house stove for growing sweet potatoes, ginger and turmeric so the soil temp was critical and had to be maintained at 80 degrees throughout the growing season.

    this is probably more info then you wanted hope it helps.


    I was wondering what sort of run  a rocket heater could manage to heat effectively in a greenhouse setting like that one.  Could it manage starting at one end of a lean to greenhouse and go 40 feet across the front and then about 20 feet along the west side and then out?  Or would it be better to have one on each end?  (not sure how that would work for chimneys tho)
     
    Dan Cruickshank
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    Location: Virginia
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    Looking over this design, it occurs to me that every place where heat is exchanged with the outdoors is an opportunity for improved efficiency. As two examples, consider the water jacket and the pipes to and from the water heater as locations where heat can be exchanged with the outdoors. It also occurs to me that my own water heater is a gas design (currently), and therefore has a heat exchanger internal to it to promote the most efficient exchange of heat from a gas fueled flame to the water being heated.

    So here's my idea: replace the water jacket with a gas water heater, after cutting the bottom off of the water heater to expose the burn chamber. I understand that it may be difficult to place a hefty water heater that high, but wouldn't it at least increase the efficiency?

    As an additional thought, if there were some way to heat the towel with the remains of the exhaust at the same time, this would then become a high class water heater ...
     
    Gabor Mairhofer
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    hello, i am a complete newbie, but with all intention to build a mass heater into our basement. i had in mind to use a woodstove, so i bought one a while ago, and also a 6" diameter twin water jacket (4 connector) heat exchanger plus a 200L puffer tank. the woodstove will wait, or i sell it as newer used, and i go with the rocket mass heater instead. my question for this topic, do i need to use the heat exchanger standing upright to utilize water circulation without a pump to the heat puffer tank. http://en.wikipedia.org/wiki/Thermosiphon
    i intend to lay the exchanger horizontally at ground level and the water tank standing nearby, or possibly elevated by 1 foot to help the flow. i as calculate, with upright mounted exchanger i need a few more 90 deg corner pieces for the exhaust pipe.
    thanks, gm.
     
    Wink, wink, nudge, nudge, say no more ...   2016 PDC and Appropriate Technology Course at Wheaton Labs http://richsoil.com/pdc
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