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Rocket-Waterheater very simple to build  RSS feed

 
Konstantin Kirsch
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Location: Middle of Germany
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Hi, some days ago I got the idea to design a rocket heater to get very simple hot water. The thing is at the usual barrel construction, that the gases get colder on passing the barrel, so they get heavier and the draft gets stronger. On the one side, the heat riser has to be insulated and has to have a significant height to get good draft. On the other side: If you cool the down going gases better, than you get a better draft.

The first idea was to construct a barrel with water on the outside. But it was to difficult for me to construct. The new idea is to use hot water boilers, fired by wood. In Germany, we call it "Badeofen". Make a google picture search with this word and you know what I mean. In englisch I found the google words: "water heater wood" which showes quite good results.

Usualy these water heaters are fired just under the cold water. Thats crasy. It's nearly that crasy as to make the fire just in the water (http://snorkel.com/hot-tub-info/snorkel-and-scuba-stoves.php) The fire has no time and space to burn hot and good. So my first Idea was to build a "J" with a insulated heat riser just beside the "Badeofen" and then let the hot gases go down in the waterheater. Then the hottest gases meets the hottest water and make it more hot. A little bit more down, the warm gases meets the cold water and heat it up. Sure, ther will be condensate at the bottom of the water heater, but you only had to let this water flow outside the house.

Than I thought: Just take two of the "Badeofen" and put water only in the second. In the first, just cut of the top and fill in fireproof insulation (vermiculite).
Than you even don't have to build a "J". You just can use the original firebox to make the fire.

If you like you can make a bench out of clay after the water heater to get a Rocket-MASS-Heater. The waterheater is without pressure, so be aware, that the hot water will drop out on getting warmer.
I just believe, that it might me very nice to have such combination of two "Badeofen" just beside a bathtub.

I don't have build it yet, but I want to share the idea.
See the attached picture for better understanding.
entwurf2.jpg
[Thumbnail for entwurf2.jpg]
rocket-heater made from two "Badeofen"
 
Peter van den Berg
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Hi Konstantin,
Your idea has got one fundamental flaw: it isn't a rocket stove, just the same firechamber as the Badeofen. In order to get the good combustion the flames has to go sideways, that's the reason why it is such a good combustor. By doing that, it will cause a vigorous turbulence which is indispensable for a thorough mixing of combustibles and air.
In short: following your idea the water will get hot, yes, but the combustion wouldn't be any better than the Badeofen in the first place.
 
Konstantin Kirsch
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Hi Peter,

As I wrote im my text, you could build a usual RMH-"J" with a heatriser and combine it with a "Badeofen" instead of a barrel. It's also easy to build a horizontal "J" under the first "Badeofen".

I believe, that the combustion is better if the fire is burning in insulated heatriser and not direct under cold water.

Konstantin
rocket-water-heater2.jpg
[Thumbnail for rocket-water-heater2.jpg]
 
Satamax Antone
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Konstantin, i don't know about germany.

But in France we used to have thoses hot water heater tanks, to use in the conjunction with a heating system. They used to have a water jacket and the hot water tank inside. So hot water from the radiators didn't mix with the hot water for washing. Often made of two tanks welded inside each other. And insulation outside.

Like the type K here: http://www.wefa-service.com/ballon_mixte_k__kr.html

They're not made like this much anymore. But you can find some in places. Look for old water heaters in skips and dump yards.

 
Konstantin Kirsch
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Hi,

my main thought of using the "Badeofen" is to use the coldness of the water to optimise the draft in the system. The usuall barrel does the job. But if you use water you cool better, so the draft gets better.
To get warm water is a nice side effect.

Konstantin
 
Satamax Antone
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Konstantin, i have understood this.

What i'm trying to explain, is that there is, out there double layer water heaters, which can be cut at the bottom to form a barrel with a water jacket. Last one i have cut had a 1 1/2 inch gap between the two barrels. You would just have to weld the bottom of the water jacket, and be done with a nice barrel with water cooling
 
Konstantin Kirsch
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Satamax Antone wrote:
What i'm trying to explain, is that there is, out there double layer water heaters, which can be cut at the bottom to form a barrel with a water jacket. Last one i have cut had a 1 1/2 inch gap between the two barrels. You would just have to weld the bottom of the water jacket, and be done with a nice barrel with water cooling


Now I got you!
I see that I'm not enough out there at the scrap yards...
 
Konstantin Kirsch
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I just found a drawing from Kirk Mobert which goes in the direction what I want to explain:
http://www.permies.com/forums/posts/preList/6199/60253#60253



The cold water is in the downstream of the hot gases and helpes the draft.

I think its much more easy to use a "Badeofen" instead of building a bell with watertank inside.

Its also possible to use a dragonheater core for good combustion, build the heatriser with some clay/adobe around the vermiculite riser and connect this to the "Badeofen".
rocket-water-heater3.jpg
[Thumbnail for rocket-water-heater3.jpg]
 
Satamax Antone
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Konstantin, that updraft downdraft arangement has been tried before. There's little to no gain to be had draftwise, as i've read. I can't remember where. But the point was that hot gases expand in the heat riser and at it's top, and find a bigger volume at the top of the barrel to quickly cool in contact of the barel top and upper sides. Then contract even more on their way down.

Here you have no increase in volume.

This two tank arangement, with the outer layer being water, to me; would seem more promising.

http://donkey32.proboards.com/post/2612/thread

 
Konstantin Kirsch
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My concern is more the weight of the gases and not the volume. From a firestove specialist I heard that the gases which go to the chimney gets cooler and so the volume gets smaller and so its right to make the diameter of the stovepipe slowly smaler. As I tried this I found that with RMH its better if the diameter stays the same or better gets bigger on the way.

I think its worth a try.

Konstantin
 
Satamax Antone
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Prety much what i was trying to explain.

http://www.permies.com/forums/posts/list/28282#282329

 
I agree. Here's the link: http://richsoil.com/wood-heat.jsp
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