Post by minervalong on Feb 6, 2018 12:04:08 GMT -8
Hi all. New here and flummoxed by all the technical info. I don't want to presume on anyone's kindness but I don't want to re invent the wheel either so thanks for you help in advance.
I'm putting up a pair of Harbor Freight greenhouses. Going to butt them together into on 10 * 24 foot structure with a single doorway between. This will allow me to shut off half the structure during really cold weather. Mostly it will be used as a weaving room to get me out in what sun is available in the winter, start some seeds early but not to keep at growing temp during the night. So I will need heat during the day with some residual heat for the night.
I was thinking of a vertical batch box rocket with a bench. Total length would be 10 ft or less. Bench would be 3 ft tall by 2 ft wide made of regular brick with a concrete paver for topper. I had planned on the square or rectangular flue tiles for the body and riser of the rocket, within a brick box with cast iron top. There is just so much info here by such accomplished burners I'll never come up with a good idea I feel like lol. Yes, your knowledge intimidates me .
Are there plans for such a thing? Does this sound feasible? Would any surfaces get hot enough to melt the polycarbonate sheets? I'd like to include a port of some kind to help heat the chimney for good draw. Do I need to run exhaust pipe in the bench and fill it or just a hollow bench? See, so many questions without answers. That's a noob for ya I guess.
I just finished a 'simple', small, mass heater that sounds similar to what you are imagining. ('simple' relative to some of the constructions on this site.) I'll include more details at my post under "Finished and Finishing".
Mine is relatively close to my twin walled polycarbonate, and I am not too concerned about reaching dangerous temperatures. I am aware that this kind of plastic will burn like crazy when it goes, so it is always a concern.
Post by minervalong on Feb 6, 2018 13:47:50 GMT -8
Thanks Wiscojames. Mine will be on the north side of the gh, so was going to replace the poly with foamboard. I'll leave room for a space and then a sheet of concrete fireboard with radiant barrier behind the actual stove. I don't think I'll need to go that far on the backside of the bench but will leave room for it. Have to replace the roof piece with something for the chimney to run through.
If I use a cast iron cooktop on to top the stove, will that give me quick heat? or should I try to figure something that is a hybrid? I don't want too much of the heat dissipate quickly. Will an 8 inch vertical batch box system put out enough heat?
What exactly do you mean by "vertical batch" box system? The Peterberg Batch Box is normally simply referred to as either the Batch Box, Peterberg Batch Box, or simply PBB.
An 8-inch Batch Box system produces a ton of heat. At least double, if not more, of an 8-inch J-tube. My Brick Body Batch Box is virtually identical to what you're proposing, though it's a 7-inch version. I divided my bench into two bells which was wholly unnecessary and made it hard to start from cold (which you'll be doing on a regular basis). Keep the bench as a single bell.
If your primary bell (surrounding and above the riser) will be all brick, you'll need to make it double-walled with a gap between the two walls to prevent cracking. If you choose to use the "standard" barrel as the primary bell (above the riser), you can build the rest of the bell system single-skinned and won't need to do anything exotic.
Just remember that in order for a bell to work, the outlet has to be towards the bottom of the bell.
Post by minervalong on Feb 7, 2018 10:27:13 GMT -8
Thanks for replying Pinhead. I'm so new to this, my tailfeathers are still wet lol. I've looked at rocket stoves for a while, but this site is sincerely technical. I'm a hands on type learner so it takes a bit to get my head around all the info. I'm afraid I'm gonna miss that one THING that makes this work, then the hubs will say I told you so.
Could I use a barrel as the primary bell (that sits over the riser) and brick between it and the siding of the gh? Would it be more efficient as mass to use plastic drums with salt water, using a container and pipe to form a slight thermosiphon rather than brick bench?
Are there building plans somewhere for a PBB? I can follow plans, the only thing I ever wing is cooking, which I'm pretty good at lol. A wrong move here is not fixed by simple addition of a spice or something. And it's certainly not a feed it to the dogs and start over deal either.
Again, thanks so much for the help. I'm so excited to have a gh/weaving room I can sit out in during the cold weather.
Post by minervalong on Feb 7, 2018 11:44:31 GMT -8
Not rocket stoves, but plenty of fireplaying and DIY, my farmhouse was built in about 1900. I have done a bit of masonry and construction. Pretty good at some thermodynamics to maximize heat retention/retardation. I'm so glad you nixed the water idea lol, that was the hubs. There is gonna be plenty of moisture in the gh as it is.
What kind of clay? Where can I source it? I've read on some threads about using plain cat litter. I got tickled at the Eureka of finding your very own claybank.
I am willing to spend a little money. I had already decided on using the new riser and at the dragon page they sell it in 1x2 ft rectangles so will source that there. Do I need to build it of firebrick or will regular brick do? I'd have to buy firebrick but can source old regular brick.
Can this be built short? Like max of 4 ft high? I'm thinking the heat rising from a six foot or better drum top would be too much for the polycarb roof panels.
The clay doesn't have to be pure, though the less "dirt" mixed in, the better. You'll need a lot so I wouldn't even try to build a RMH if I had to buy it. Just dig it up out of the ground.
I'm somewhat confused about what you're saying about the riser. Are you talking about buying the 1x2 ceramic fiber boards from Dragon Heaters? If so, the material will work on its own as a riser. You definitely don't want "regular" dense brick inside the riser. You could build a brick "form" around the outside of ceramic fiber board if you wanted to but it won't really help much at all.
For the body of the stove, you can use either firebrick or red dense brick. Firebrick will perform better (hold a little more heat in the firebox) but both will do. I've used red brick in both of my long-use Batch Boxes and haven't seen any disadvantage as long as the dimensions of the firebox are kosher.
Building the entire thing 4' high would be tough; you need a 1-foot gap between the top of the heat riser and the barrel so that would make the firebox and riser 3' tall max which would be pretty cramped (especially if you plan on going with an 8-inch firebox). Even a 6-inch PBB would be tough to stuff in a 4-foot space; the riser, itself in a 6-inch system is 57" tall. You could cut that down to 3' and fit it into a 4-foot-tall barrel if you put the firebox on the ground. It can be a pain to load that way but it's doable.
Quick question, does it matter at what height the flue goes into the bell? I know it needs to be low on the riser cover, but how low into the bell?
Generally you want:
1 - as low as possible, while still being higher than the exit (see #3 for more detail)
2 - as slow a flow as possible to avoid creating turbulence
3 - no direct path between the entrance and the exit (otherwise the momentum of the gases can carry them directly from entrance to exit before the gases have a chance to stratify)
I have a dead-end bell where the entrance is a standard metal tee with the bottom lip exhausting about 6" above the floor, pointed directly at the far end of the bell (7' long). The exit is directly beside it, an insulated piece of straight flue elevated 3.5" from the floor. Ideally it would be a bit higher, but I don't seem to have any flow problems (I feed it with a standard box stove with a tall chimney/ lots of draft).
Since I am building a 6" J tube heater in a greenhouse I thought I could just tag onto this thread. I mentioned before that all the information I had prior to joining here came from You-tube and the Wisner book. In the book they indicated that a cob mix might be less than ideal in a greenhouse because of the already damp environment. Wouldn't the heat from the ducts in the bench dry out the cob regardless of outside humidity? Also I have lots of clay and also pure sand on my property. How much difference may there be in the heat storage capacity between the cob and just sand? Filling the bench with sand would definitely be a lot easier.
Hi Minervalong. From the sounds of it, you might find value in spending some time in the reference library. The amount of info on this site can be daunting at first, but gradually the common principles come clear. Beyond that, the folks on this forum are most willing to help you out.
There is an old permaculture saying: better to do protracted and thoughtful observation rather than protracted and thoughtless labour.
One important piece of design/build I'll mention here is: anywhere you are transitioning, turning a corner in the gas path, you had best open the cross-sectional area (CSA) of the channel to at least 150%. This will reduce turbulence and eliminate constriction. Also, if you bell entrance port is at the same end of the bench as your exit port into chimney... heat distribution to the far end might not be very good. Better to run a flue within the bell (even just a 6" steel pipe) to the far end and then let the gasses work their way back to the exit.
How much difference may there be in the heat storage capacity between the cob and just sand? Filling the bench with sand would definitely be a lot easier.
It would be easier... but the material in the bench is intended to extract heat from the flue gases and conduct it to the surface of the bench. The most insulating material is air (air trapped in a matrix of other material, be it glassfibre, polystyrene, straw or sand).
Experiment: How much air in there in a glass of sand? Fill a glass with sand to the top. Fill another glass of the same size with water. Slowly pour water into the sand glass until it is about to overflow. How much water was used from the water glass? It is trickier to make the same experiment with a glass of cob...
Now think of the cob where there are clay particles (smaller than sand particles) filling the space between the sand in the mix. There will be less air in the cob so less insulation and more conduction. How much of a difference will be dependent on the % of clay in the mix.
If it is worth the extra effort to have greater heat absorption & conduction only you can decide.
Good example and since I have a large amount of mostly clay soil right outside the greenhouse I will go that way to fill the bench in the greenhouse. I assume that the cob eventually dries. Is it advisable to run the heater without the top of the bench being capped so that the moisture in the cob can escape and then cap it later?
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deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
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