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Dragon Heaters Castle Build Exhaust flow  RSS feed

 
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I was at the Dragon Heaters website today and was looking at the Castle Build model. I like it a lot but I am confused about the exhaust flow. They show is rising and settling in each bell and as I understand the drawing, the bell or cover over the main heat riser does not have falling exhaust gasses around it?. Has anyone looked at this? I really like the rocketmass stove idea but do not have room for the bench, but something like this would work, I just am a bit confused with the exhaust flow.

Thanks

Kevin
 
Posts: 243
Location: near Houston, TX; zone 8b
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Kevin,

You are correct in thinking that the exhaust does not fall down around the heat riser. In fact, the space around the heat riser is insulated with loose perlite. The exhaust is routed through the stacks of chimney flue liners and warms them up. Each stack of chimney flue liners function as a bell (as opposed to the flue which is what warms a bench in the traditional rocket heater). With a chimney it has great draft; it doesn't need the cooling effect of a metal barrel. If you check our blogs, you can read our efficiency and emissions numbers which are excellent. We also have an explanation of Bells vs. Flues.

Cutting and stacking the flues for this build will require about a day with 2 people. Then, if you want to cover it with stone, it will take another day. Complete instructions are provided with the DIY kit and you don't have to build it outside first.

I am a partner in Dragon Heaters.
 
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Kevin,
I got to play with one of these at the Mother Earth News Fair in PA in September. The standard RHM surrounds the insulated riser with a 50 gallon drum which acts as a radiant surface to heat the room up quickly while adding a bit to the thrust of the exhaust because the (relatively) cooled gas wants to drop. The "castle build" uses stacked ceramic chimney flues instead of the 50 gallon drum which means not enough room for sufficient insulation on the riser AND the falling gas flow thing to happen concentrically (there are other benefits to using ceramic flues that I will go into in a bit).

So at this point where a typical RMH exhaust goes down and then out through a stovepipe embedded in a thermal mass bench, the Castle takes a page from the Masonry Heater playbook and instead the super insulated heat riser dumps into the "bell" next to it about half way up. The exhaust flow pattern in a bell is still down and out, but in the hollow "bells" the exhaust loses its direct momentum and the hottest gas rises to the top and pressure pushes the coolest gas out the exit into the next bell where it happens again, then the much-cooled gas is pushed/drawn out a standard drafting chimney at the base of the last bell.

Each tower of double-thick chimney flues covered in cob or stone facing constitutes a significant thermal mass and and also an efficient, smaller footprint radiator to store and slowly release the heat from the hot gasses within without being uncomfortably hot at the base where people would most likely come in direct contact with it. The use of ceramic flues instead of metal stove pipe & drum also has the benefit of making this RMH legally a Masonry Heater instead of a non-code-approved woodstove. I want to build one of these myself but I'm busy building portable units for a greenhouse client and a client who lives in a school bus, so wifey says I have to wait until spring to put a hole in her living room floor for the foundation of my "Castle".
--Chris
 
Kevin McCune
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Thanks Guys, I missed that there was a blog, the drafting info is what I was concerned about. Now for the floor loading.. I could put it in the basement, but I think its a very attractive design and people should see it.
Kevin
 
Chris McClellan
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At 1200ish lbs its a lot lighter than a properly sized cob bench mass but still something to pay attention to supporting properly.
 
Kevin McCune
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The 6 inch system is listed at approximately 1800 lbs. and has usable heat that should heat my house in the late spring, early fall and help out a bit in the dead of winter. The 4 inch one is just too small for my location. I would like the 8" one but thats 3000lbs. I don't know maybe I should just bit the bullet and build the 8" one in the basement. That would force me to evict my daughter back up to her room, but I would get my office back!


Kevin
 
Chris McClellan
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Sounds like a win-win for you.
 
Cindy Mathieu
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Location: near Houston, TX; zone 8b
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We just (this morning) posted a blog of a new design for the 8" using steel drums as a bell. It has excellent efficiency and stores the heat in fireclay bricks. However, it is 9' tall (3 55 gal drums), so it may not work in your basement.

Later this week, we will have some information about an 8" castle build with a bench and an oven. It is partially completed on the demo slab. If you place the chimney flue liners on a hearth pad, the weight will be spread out sufficiently that it is not beyond the capacity of ordinary construction. Since heat rises and the burn tunnel is on legs with insulation all around it, the bottom of our builds don't get very warm.
 
Kevin McCune
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To which system are you referring, in regards to the hearth pad?


Kevin
 
Cindy Mathieu
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Location: near Houston, TX; zone 8b
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Kevin,

I need to backtrack a little bit and not promise anything about the capacity of your floor. You would need to check with a contractor or structural engineer to be sure.

We have a pretty good weight estimate on the 6" castle. At this point, we don't have weight estimate on the 8" because the build isn't tested yet. The walls of the 24" x 24" flue liners are substantially thicker than the 18" x 18" ones we use in the 6". Consequently, the total of it will probably be heavier and it will definitely have a larger footprint than the 6".

Stay tuned,

Cindy
 
Kevin McCune
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Don't worry I am checking into the floor. Problem is its a w truss and the calculations are not as straight forward as a beam floor.
I most likley will not do anything till spring after I see what tax season will do to me. Kids moving in and out, college, adding and subtracting dependence...

Kevin
 
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Location: Kansas Zone 6a
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That is the weight of a waterbed or large gunsafe. You can't just put it in the middle of the room willy nilly, but we are not talking monster footers and floating concrete columns like a masonry heater.

There are ways to increase the load bearing ability of trusses by sandwiching plywood on each side (creating a box beam) but I don't know the specifics.
 
Kevin McCune
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3000 lbs works out to ~ 250 lbs per sqr ft. The corner that I want to put it in is over the office (daughters claimed bedroom area). That corner of the office has a diagonal wall. About 40-50% of the weight would be on the unheated side. This I can brace at will. The rest of it will be over the heated side where bracing would be undooable. But the diagonal wall with a hearth pad may do the trick. Lots of time to figure it out.

Kevin
 
Kevin McCune
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Cindy,
I was just at your website again, it looks like I you have been building! Can you give me a short explanation of the 8" castle build system, I envisioned it looking like the 6" set up.
I like the plenum to connect the flue pipe in the new 4" pics. Would it cause any problems to build it a little higher and run the pipe straight out the wall? To a 3 story chimney?

TIA

Kevin
 
Cindy Mathieu
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Location: near Houston, TX; zone 8b
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The 8" castle which we built is actually one big chamber. We used 24" x 24" chimney flue liners to create a 24" x 36" rectangle. We also lined the top of it with fireclay bricks to absorb some of the heat. The bench is the trickiest masonry element, but we had requests for a bench. The bench and the oven are optional. We tried it without the fireclay bricks and the bench got too hot to sit on. So, we are still testing.

You want the exhaust to come from the lowest point of the bell, so that only the coolest gases leave the building. The bell system has plenty of draft, so you can probably get the exhaust to your chimney running it out of the lowest part. Does this answer your question?
 
Kevin McCune
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Ok a bench.. that explains it. I couldn't figure out what it was. That and the oven are good ideas. As for the flew pipe, my idea was to do just like you did on the new 4 inch pic, but build it higher and exit out the side. So it would be exiting the bell at the bottom, but then going up for 4 or so feet and then going sideways through the wall. The wall it will be going through is into the "furnace room" where the chimney is located. I just didn't want to run it along the floor in there. Like I said I'm not doing anything until after tax day so it has time to evolve!




Thanks for the info!


Kevin
 
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