RMH in TN

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RMH in TN

Postby wileythenord » Wed Oct 01, 2014 5:30 pm

To start an update without bumping a dead thread (see http://www.permsteading.com/viewtopic.php?f=6&t=477) I'll use this space to ask questions and post updates on my own RMH build.
Background:
We have an 864 sq ft basement that we are currently living in while we are building the house (debt free). My wife and have identified the area that we plan to build our heater, it is a space on the east wall that is approximately 9 feet wide and clear on either side for another 5-7 feet so I don't have to worry about accidental combustion. Our plan is to build sort of a Tabletop/bar instead of a bench since that current space houses a dining room table and this would allow us to put a flat top of some kind and bar stools and still use it as such. Based on calculations from Rocket Mass Heaters by Ianto Evans and Leslie Jackson that should give us roughly 5-6 ft of "bar space and 3-4 feet where the feed tube, burn tunnel and heat riser will be contained.

Some questions:
1) Would an 8" system be overkill?
2) I'm not sure if 6 feet doubled back on itself is enough to suck out all the heat from my 8" system?
3) I know the temperature should be a lot lower in the bench duct, which type of stove pipe do folks typically use? I figured I'd need black stove pipe for my "thimble" between the manifold (if thats the correct term) and the rest of the duct, but after that could I use HVAC duct or would I need to keep black stove pipe?
4) Have any of you ever attempted to cast the riser in 2 pieces (or 4 pieces) and then join it after drying on top of the cast core? Sort of like casting the riser in 30" X 4" "Bricks" and then wrapping them with rock wool, chicken wire, and perlite? Does that make sense?

Thanks guys, I'll try to keep this updated, We are probably a month and a half away from temps in the 30s F, maybe longer, but I'd like to have this thing up and going by November anyway.

PS I'm working on a drawing in sketchup, I'll post it when I'm done.

Thanks Matt, your recent foray into a PBerg batch heater is really "firing me up!"
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Re: RMH in TN

Postby thickstrings » Wed Oct 01, 2014 6:38 pm

I can take a stab at a few things Willey. 1st, I think a 8" would run you out of a 864 sq ft. room...2nd, you don't have to suck all the heat out of what you made.....you can just let it go out the exhaust. 3rd, Black pipe for the 1st part will work good. 4th, I have never tried to cast it in parts , although its been done . I think the clay you showed in the link is probably good...its red from iron in the soil....do the tests then add stuff as needed......
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Re: RMH in TN

Postby wileythenord » Wed Oct 01, 2014 6:44 pm

I wasn't sure on the size, I based it on someone elses thread that planned a 6" system for a 900 sqft space and I believe his advice was to go with 8" for that space.

This week I'm making some clay bricks and firing them in my concrete block rocket mock up I've got in the front yard to see how it handles the heat.

I really want to grab as much heat as I can though, otherwise it will lead to more firings right?
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Re: RMH in TN

Postby thickstrings » Wed Oct 01, 2014 8:34 pm

I believe a 8'' system can push 50' of bench...subtract 5' for every elbow or tee. That's not counting the chimney. As far as the firings go, a lot depends on the systems efficiency ,the materials you made it with ect. It will still take a certain amount of time running to heat your mass,6 or 8. A fellow can adjust the amount of heat that goes to the bench by covering the barrel with cob or insulating the inside of it....less immediate heat, more down stream....least that's the way I see it....maybe someone else knows more....
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Re: RMH in TN

Postby matt walker » Wed Oct 01, 2014 9:30 pm

Oh, a new build! Fun!

As for sizing, I'd go 8" if you can get the materials. You can run half loads if you don't want the full output, but the extra power is nice to have. Not to mention, you can use a wider range of fuel sizes, and the transfer surface in the mass is much larger so you can get heat into the mass quicker(I think).

That's a short run, you will have fairly high exhaust temps if you don't shed some more heat, but it will work. Put your mind to where you might stash another length of pipe/mass, or another barrel radiator, or something. Benches tend to create useable space rather than eat it up, in my experience. I also think you will be missing out if you don't have the warm place to sit, it's really freakin' fabulous. Just some thoughts, not necessary, but.....

HVAC ducting is fine.

I would cast the riser by following the way I do it in my cast riser video, you can lift it up and move it around easily if/when you need to get in there and make changes. You will make yourself a whole lot of work by doing it in parts, and it will almost certainly crack and fall apart if/when you try to move it. On the other hand, new ways of doing things are cool, so if you are inclined to go for it, keep us posted.
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Re: RMH in TN

Postby wileythenord » Thu Oct 02, 2014 11:33 am

matt walker wrote:As for sizing, I'd go 8" if you can get the materials. You can run half loads if you don't want the full output, but the extra power is nice to have. Not to mention, you can use a wider range of fuel sizes, and the transfer surface in the mass is much larger so you can get heat into the mass quicker(I think).

Materials won't be a problem, I have access to all the straw, clay and rock I can stand and sawdust for that matter
Image

matt walker wrote:That's a short run, you will have fairly high exhaust temps if you don't shed some more heat, but it will work. Put your mind to where you might stash another length of pipe/mass, or another barrel radiator, or something. Benches tend to create useable space rather than eat it up, in my experience. I also think you will be missing out if you don't have the warm place to sit, it's really freakin' fabulous. Just some thoughts, not necessary, but.....

hmm, if I build it 40" tall and 4 feet wide I have lots of room, I'm just concerned about the extra turns. But after going back and looking at your build I think I'm fearing turns more than I should, you have several doublebacks in your bench and look like you span more distance than I'm talking here.

matt walker wrote:I would cast the riser by following the way I do it in my cast riser video, you can lift it up and move it around easily if/when you need to get in there and make changes. You will make yourself a whole lot of work by doing it in parts, and it will almost certainly crack and fall apart if/when you try to move it. On the other hand, new ways of doing things are cool, so if you are inclined to go for it, keep us posted.

I'm not interested in reinventing the wheel just yet!

Here is my initial sketchup, but I think i'll go back and add some extra ducting and lower the core and barrel. The bar is 40" tall, that back wall is 9ft wide, ceiling height is 7.5 feet. My picture is rough, you have to imagine a 3rd dimension, the top duct would be exiting behind the barrel and going up the wall. BTW my walls are 8"block walls poured full of concrete, should I be worried putting this system against it? I don't know if I could count it as mass or not, but after the bench comes up to temp I'm sure that wall would start to soak it up as well.

Image
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Re: RMH in TN

Postby matt walker » Thu Oct 02, 2014 3:30 pm

Looks good. Don't worry about the block wall, that will be fine. My materials comment was more about the flue pipe, 6" is common and inexpensive. 8" can be hard to find and expensive. Don't sweat the corners in a system that short, you could do spirals and it would draw fine. I think the 5' for corners is inaccurate at best, although it's useful to give newbies some sort of guidelines. I would say start with what you have drawn(plus the additional flue you mention above) but install some T's as cleanouts at a point where you could potentially add a bench in down the road if(when) you end up loving the thing and wanting more.
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Re: RMH in TN

Postby ByronC » Fri Oct 03, 2014 1:33 pm

Nice plan. I'll be starting my 8" RMH build soon, which is going indoors in an above grade cabin that sits on a short block foundation with 32" high crawlspace underneath. My plan is to first build a raised concrete and block foundation for the RMH base. I've been thinking about constructing it in such a way that the bottom of the 8" J-burner will be close to the actual floor level, to help keep my barrel's top "cooking" surface as low as practical.

Anyway, from your drawing, are you going to have the J-burner and barrel that high off the floor? 55 gallon barrel? Maybe you've got sufficient ceiling height for the clearance needed to be able to get the barrel on/off the heat riser etc?
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Re: RMH in TN

Postby wileythenord » Mon Oct 06, 2014 12:05 pm

Originally I had planned for it to be elevated, but now that you guys are talking to me about it I think I'll put it on the floor and add another run of ducting to increase my heat absorption. Hopefully I can modify my drawing today and get it posted back.

I started sourcing some materials this weekend. I'm having a tough time locating Perlite, is horticultral perlite acceptable? Its pretty coarse, but I can buy it in a 4 cuft bag for $25 at a (somewhat) local nursery.

After putting some balls of my clay in the fire I believe it will work just fine. Is fiberglass the common binder used for cores?
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Re: RMH in TN

Postby matt walker » Mon Oct 06, 2014 3:46 pm

Yeah, I like the coarse horticultural perlite better. It does suck up some water, but you will drive that out of it and the large size means larger air space so better insulated. At least, that's my theory. I do use fiberglass, refractory suppliers recommend stainless needles which in practice look more like stainless bobby pins. If you use fiberglass the trick is to not use too much, you don't want any large, dry sections of it in there. Just fine hairs evenly distributed.
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