Bricks for the box of my cob bench

I forgot to mention, I will do it tomorrow too after I am done with cobing the burn chamber

Bacon Lee wrote:
I forgot to mention, I will do it tomorrow too after I am done with cobing the burn chamber

I would consider wrapping the final cob with a wire mesh of some kind. Hardware clothe, chicken wire, whatever I had that was cheap or laying around.

I would also tend toward making to perlite clay mix with a little too much clay, as opposed to making it with too little clay. If you use too much clay, it'll get hard and hold together, but insulate somewhat less than the optimal mixture of perlite and clay; whereas, if there is too much perlite (or too little clay, which is just a different way of saying the same thing) it will crumble, and end up laying on the bottom of the barrel's floor.

And as previously discussed, mixture ratios are only educated guesses. You just have to "feel" what is the right mix as you mix it up.

Maybe someone reading has used Lincoln 8, and can recommend a starting point. If not, my suggestion is not too wet, but with a small film of clay sticking to your hands, but still enough perlite that the "snowball" feels *not* like clay. My starting guess is a ratio around 1:6 (clay:perlite). But again, that is only a guess, and you have to adjust it according to what you feel in your own hands.

No, Erik, I insulate my heat riser with Roxul. Already bought Roxul

Bacon Lee wrote:
No, Erik, I insulate my heat riser with Roxul. Already bought Roxul

Even easier!

Allen and all, please take a look at my photos with the locking ring. If you could please let me know if I am ok doing that. I just want to make sure before I do it tomorrow

Thanks Sandy

And yes, you can offset the barrel, but not quite as much as you show. When you put the insulation on the riser you want to still have at least 1 1/2" of space between it and the barrel. With rockwool, I would aim for a minimum of 1" thick at the corners and 3" thick on the sides.

I tried to insulate the heat riser today. Oh my, it is very hard to work with Roxul. It’s a bad choice. I should have gone with perlite. This morning I insulate the burn chamber with perlite, I didn’t have a form, I made temporary unstable form around the chamber and insulate it. It took me more than an hour to insulate the burn chamber this morning and I am sure it’s good. This Roxul took me more than 3 hours, not done yet. I am not happy with it and I am very worry about it.

Here it is about Roxul:

Roxul is soft and seperated easily, worse than cotton ball. At least cotton ball interlink into each other and form a ball. Roxul are not that, Roxul is soft, seperated and not interlink into each other. With this we can’t just use wire to tired them up, because they will seperated and falling apart. We have to use the wire mess to hold them together.

Also, Roxul is puffy so now we have to put a lot of presure, press hard on them to have them compress into the heat riser. To do that which mean we have to compress the wire mess around it as well. And this is why it is not good, very hard work.

What I did was: I took wires to wrap around the wiremess on the heat riser, and then I twist the wire mess to tighten it and to compress the Roxul. The problem is the wire broken as I twist it. I had around 20 times wire broken and only 4 stay on. But then all of a sudden one of the 4 broken on it own when I didn’t even touch it. This is worry me. What if after a while the wires broken one by one, which mean I have a mess in my barrel. And I have to knock off the cob to take out the barrel to redo thing…

Look at the photos, it doesn’t look good at all. We should not go for Roxul. I am thinking of undo this insulation, buy more perlite and redo my insulation on the heat riser or I have to make cylinder around my heat riser and put this Roxul in just like we deal with perlite. That way it will be a shorterm and will not give me a mess soon. I work hard to have my rocket heater last for longer. I don’t want to have a mess after a while and have to knock things off to redo. I rather do it right. Should I make a cylinder around my heat riser and compress the Roxul in there?

"
Glen: Roxul came in sheet, I think the sheet is 3" thickness. I compress that sheet onto the heat riser. You mean 3" thickness before compress, right?

As with most types of insulation, it isn't the rockwool that is insulating, it is the air spaces caught inside of it. So compressing it reduces the R value. So try not to compress it. If you do you do, just try to do so as little as possible.
With regard to the wire mesh, that looks good.
With regard to the wire breaking, my first guess is you are just twisting it too tightly. A little trick to tighten wire like that is leave it loose enough to start a little loop, then insert a nail into that loop and use the nail to give you leverage to twist the wire loop into a circle once or more. That tightens the wire.

What is the wall beside the rocket stove made of?

My goodness, no one give me tips about not to compress this Roxul thing. Are you sure we don't compress them? I totally compressed them llike crazy. I kinda made a pretty plum into a skinny supper model . It think I have to undo this Roxul thing, but I want to wait for others to make sure we don't compress them, my goodness

You mean the wall? That's the wall of my house. I have no idea what it makes of, but definitely not of wood. Should I put some of this Roxul by that side where the window is.

Bacon Lee wrote:
You mean the wall? That's the wall of my house. I have no idea what it makes of, but definitely not of wood. Should I put some of this Roxul by that side where the window is.

If I recall correctly, the ASTM standard for masonry heaters is a 4-inch air gap between the masonry heater and nearby structures, like the wall of your house. It is better that it is not a wood-frame wall. It just looks very close to where you've set up the hottest part of the RMH (the barrel). What is the distance between the wall and the barrel and the nearest fire brick of the fire box (feed tube, burn chamber, fire riser)?

Bacon Lee wrote:
My goodness, no one give me tips about not to compress this Roxul thing. Are you sure we don't compress them? I totally compressed them llike crazy. I kinda made a pretty plum into a skinny supper model . It think I have to undo this Roxul thing, but I want to wait for others to make sure we don't compress them, my goodness

I wouldn't worry about it too much. It is a matter of what works best, not a question of it not working when compressed. I doubt I'd redo it. Although it did look like the corners of the brick were showing through the rockwool. That's not ideal. But maybe not a terrible error, given that is where the brick is the thickest, and if that is full size brick, there is over 2-inches of fire brick at that point, measuring along the diagonal, from the opening to the outer corner. That'll take more than an hour for the heat to saturate, I expect, and if you are not burning much longer than that, I doubt it'll really make a big difference.

But see what others think.

I know, one more guy butting in with an opinion. But I believe that compressing 3" down to 1" will lower the R value but will be more than 1" puffed up. So if you stuff insulation in a 3" gap like inside a pipe around your heat riser it will be more insulated compared with 3" puffed up even though it will be less than the if the whole amount stuffed in was left loose. And your wire I'd say you either have the wrong kind or are winding it too tight. Some soft iron wire will be easy to wind on and not break.

Anyway Bacon, you're doing a very good job and i've been closely following this whole thread with interest. Keep up the good work.

Phil and Erik:

Yes, the wall is wood frame structure. If I put the barrel on, the barrel is only 3" from the wall (Unless I offset this side too then it will be 4" from the wall).

I tried to understand Phil message but I didn't really get it yet. Phil, you mean compress it will be more insulation or let it loose will be more insulation". Or you mean I should have a tube around the heat riser and stuff Roxul in it? How effective this tube stuff Roxul is compare to let the Roxul loose around wire mess with no compression?

I don't want to leave my heat riser this way, because I am afraid the wires broken soon and I have to knock out things to redo. I rather redo it now. That's why I stopped it yesterday without finish it. My concern now is What option do I have which is should fairly effective and easy for me. I still have the wiremess, should I undo this and have Roxul loose inside the wiremess with 3" straight edge and 1" at corner like Glen said? Should I do the tube and stuff Roxul in it? How effective this one compare to the other please.

Erik: The wall is 10" away from the burning tunnel and things.

Bacon Lee wrote:Erik: The wall is 10" away from the burning tunnel and things.

That seems pretty close. What are you doing to protect that wall from the heat coming off the barrel?

Erik: I already had 3" perlite around the burn chamber. Should I put Roxul by the side of my brick-wall close to the house wall?

How come Satamax, Glen, Allen, Shilo, Thomas... didn't say any thing. I want to wait for everyone's opinion before I redo my heat riser insulation. Erik, please help me with English issue. What does Phil mean? Let Roxul loose is better insulation or compress it is better insulation?

Bacon Lee wrote:

Yes, the wall is wood frame structure. If I put the barrel on, the barrel is only 3" from the wall (Unless I offset this side too then it will be 4" from the wall).

Full stop. I would not do that. I would go so far as to say this is a fire safety concern. I would suggest this become the topic of highest concern at this time. Maybe I am just misunderstanding you, and maybe what you are doing is perfectly safe. Or maybe you are planning your RMH too close to that wall. Far better to find out now.

That barrel is going to get at least 500-600 F at the top, and quite possibly 200-300 at the bottom. And this is *not* a zero-clearance installation. I think of the barrel much as I do a traditional wood burning stove. You may recall Ernie Wisner and some of the reference materials speaking to this point. When you are planning your building space, you have to think of the exposed barrel as a traditional wood burning stove, in terms of the heat it is throwing off, and how you protect building surfaces from that heat.

This means ceilings, floors, and walls, as well as anything else within 4-feet of the sides of the barrel and exposed fire brick. Now there may not be any exposed fire brick when finished with the build, but there is always an opening to the feed tube, and that is treated like other fire-burning openings, such as fire places and wood burning stoves.

ASTM-E1602-3 is the standard reference for safe clearances of masonry heaters. These are different than for wood burning stoves, and open fire places. A RMH incorporates elements of each of these construction styles.

Bacon, I understand Phil as saying that pushing the rockwool together like you have done is fine. No worries with how you packed the rockwool in tight. That's the part that speaks to your installation.

He then added a theoretical observation. He also was comparing the R-value of 1-inch of unpacked insulation to 3 or 4 inches of that insulation packed into a 1-inch space. He thinks that the 3 or 4 inches of insulation packed into 1-inch of space will have a higher R-value than the unpacked 1-inch insulation; but also a lower R-value than if the 3 or 4 inches of insulation was unpacked. Maybe that is true, I do not know, and I do not recall any studies addressing that point.

Why didn't anyone else say anything about the barrel being 3-inches from a wood-framed wall?

I expect the answer is the same as in my case - I didn't realize that was what you were doing.

Off the top of my head I do not know of a safe way of putting the barrel only 3 or 4 inches away from a wood-framed wall. I think you'll end up catching that wall on fire one of these nights. I can't imagine anything else happening.

So let's talk about that wall. You say it is a wood-framed wall. That means there are wooden studs inside it, most likely 2x4s. What is the outside surface? Plaster?

Erik: When I did the wall of brick around the rocket heater, I have that wall 1/8 away from the wall. Because I was thinking when I have to break down the rocket heater and sell the house, the house is ok on it's own. Now, should I slide a metal sheet into that slot to protect the wall? Would that be good?

Erik: It is woodframe and this http://www.homedepot.com/b/Building-Materials-Drywall-Drywall-Panels/N-5yc1vZbb52

You scare me a lot Erik. Now I really thinking of knock out the whole thing and start over again one feet from the wall.

Bacon Lee wrote:
Erik: It is woodframe and this http://www.homedepot.com/b/Building-Materials-Drywall-Drywall-Panels/N-5yc1vZbb52

OK, that's your basic drywall, sheetrock, etc. It does has a fire rating, but it is *not* the kind of thing you want your wood stove pressed right up against! (And 4-inches is "pressed right up against" in this case.)

This is a serious problem. This is only my opinion, but I would not put my barrel anywhere near that close to a wood-framed wall. I think doing so is more likely to catch the wall of fire, than not. This conversation really should have started here.

You're going to need to read up on fire safety and protection for wood stoves, namely heat shielding. I think what you will discover is you need to get some metal sheeting, about 6-inches shorter than your wall height, and 29-gauge or thicker. The width needs to run along about 10 feet of your wall, which is a minimum of 4-feet past both sides of the barrel (the barrel is basically 2-feet wide, and you want heat shielding to extend beyond that by another 4-feet in each direction.

If you want to get more accuracy, you can get a four foot piece of wood or a tape measure, and mark everything within 4-feet of the outside surface of the barrel. Anything within that 4-foot radius (or 5-feet from the center of the barrel) needs to be able to withstand very high temperatures, like those thrown off by a wood burning stove.

You can make the metal heat shield look pretty by covering it with non-flammable tile, brick, plaster, etc, but none of those things add to the heat shielding characteristics of the heat shield. Only the metal does, and ONLY IF it also has an inch or more of open air space behind it (so that the metal shield is between the barrel and the air space).

Then there are details about how to hang the heat shielding. You do not put any fasteners (screws, nails, etc) directly across from the barrel, and you cover the fastener with a non-flammable thimble, or whatever it is called. I recently saw an interesting design that seems to get around this by using a U-shaped bracket screwed to the wall, and then onto that, the heat shield is fastened. See the inset illustration on page 7 of this PDF:

http://dps.alaska.gov/fire/TEB/docs/woodstovesafety.pdf

In fact, that is a pretty useful PDF for other aspects of a safe installation.

Now, if you change the location of the barrel so that it is no closer than 4-feet to any wall, you don't need to worry about heat shielding your wall.

And some of these details change by location, depending upon what your local code happens to be. Some places, for example, will say 3-feet is a safe distance instead of 4-feet. And many codes will say that if you have a proper heat shield (as described above) you may reduce those clearances by 50% (3-feet becomes 18-inches; 4-feet becomes 2-feet).

If your local code follows the ASTM standard, then the masonry parts (like the bench, for example) can be as close as 4-inches from that stud, wood-framed wall. And some people have filled in that space with perlite-clay insulation, instead of leaving it open. It depends upon your local code if you can do that. If I recall correctly, you do not have a local code you have to follow, is that right? Or am I confusing this with another thread?

Bottom line?

Heat shield the wall. Then you will still have to move your fire box (all the fire brick) so that the surface of the exposed barrel is either 18" or 24" away from the metal of the heat shield (or the surface of the decorative material you use to cover that metal, the brick or tile, etc). But go by your local code for the details.

If you can get by with an 18" distance, then the center of the barrel needs to be at least another 12" farther from the wall (or 30" which is 2-1/2-feet). If 24", then at least 36" (3-feet). Personally, I am more comfortable with closer to 36" even with heat shielding. And standing 4-feet away does seem to be sufficiently far away from the barrel to be safe from catching things on fire, like books, shelves, TVs, and what not.

But when it comes to burning my house down, I really try to be a little on the paranoid side. You can be too safe, and never burn your house down, ever. Or you can be not safe enough and eventually burn your house down.

Bacon Lee wrote:
You scare me a lot Erik. Now I really thinking of knock out the whole thing and start over again one feet from the wall.

Unless I am completely misunderstanding you, and the picture of that wall which you tell me is wood-stud-framed wall, I think you should be scared.

On the bright side, you are finding out now, when really not very much work has been done (I know it seems otherwise, but compared to having completely built this thing, and THEN finding out you need to move it, or move that wall, looking at it this way, you've not done much of the work needed to complete the job). So that's good.

And finding out *before* you burn your house down is *really* good news!

However, you need to move it farther than that. I'd say at least two feet (three would be better) if you use heat shielding on that wall. If you do *not* use heat shielding on that wall, then the center of that barrel will need to be 5-feet away from the nearest wood-frame wall. Just remember that the barrel is basically 2-feet wide, and that's a radius of 1-foot, so add 1-foot (12") to whatever distance you decide is a safe distance for the barrel to be to that wood-framed wall (or the face of the heat shielding).

And the bench part may be fine as it is. I don't actually recall how close that is to the wall, or if it even runs along side the wall. But it is easier to protect the wall from the heat in the bench, because the heat in the bench is going to be so much less than that of the barrel. The barrel is the biggest concern, in terms of heat and clearance to nearby objects and building structures.

Mine is a little too close to the wall. If I knock it down and redo it further away from the wall, should that be ok, right? That video the Winser made a rocket heater during their honeymoon, that heater is running along the wall too, is close to the wall too, but they didn't do heat shield. But my top is NOT 4 feet from the celeing with exposed wood frame. My green house is only 7 feet high, and the barrel alone already 3 feet. I think the top of barrel is only 3 feet away from the wood frame celeing.

Bacon Lee wrote:

Mine is a little too close to the wall. If I knock it down and redo it further away from the wall, should that be ok, right? That video the Winser made a rocket heater during their honeymoon, that heater is running along the wall too, is close to the wall too, but they didn't do heat shield. But my top is NOT 4 feet from the celeing with exposed wood frame. My green house is only 7 feet high, and the barrel alone already 3 feet. I think the top of barrel is only 3 feet away from the wood frame celeing.

Sounds like you will need a similar heat shield on your ceiling too.

I just flipped through "The Book" looking for fire safety information. And I can see how you came to set up your stove the way you have.

I did not find clearances discussed in that book! Of course, for Evans, this was not much of a concern, because he was building this inside a COB HOUSE. And dirt doesn't burn all that well heheh. But more that this, the book is filled with pictures of people building their RMH which are obviously far, far closer to their walls than I am suggesting.

But I cannot speak to what others decide to do. All I can say, is that *I* am not going to suggest it is safe to build a RMH (especially the very hot barrel) closer than code specifies for a wood burning stove, to a wall or ceiling or floor. Same applies to furnishings and other objects we carry into our homes.

Why the Wisner's made their cabin build as they did, is a very good question. But I'll leave that as a point for either Ernie or Erica to address.

I know elsewhere Ernie used the number 125 F as what he felt was a safe temperature for a wooden floor under a RHM. I would have to say the same for a wall or ceiling. The lowest temperature I have been able to find that caused a problem in a wall was 170 F, and caused by a hot water pipe. But using 125 F adds a measure of extra safety, and that is a good thing when it comes to whether or not one is going to burn their house down.

My first build, for example, I was seeing temperatures rising toward 150 F near my wooden deck upon which my rocket stove was built. That was far too close to 170 F for my comfort, so I tore it all down to the floor of the burn chamber, and then made that the floor of an air gap I installed below the new floor of the burn chamber. (I think I have previously mentioned this.) I have not gotten over 100 F since the rebuild. In fact, I have yet to reach 90 F, but I may on colder days when I burn two or more times a day, especially if I have to do that several days in a row.

My point is, watching your actual temperatures during operation is very important, especially during the first few months of operation.

I really do not want my ceiling to reach 100 F. I do think 125 F has to be safe, after all, summer time heat can rise higher, and certainly does in the attic.

In any event, be careful. You can with minimal effort knock down part of the brick surrounding wall, and then move the location of the fire brick (and therefore the barrel too, of course) so that you have safe clearance. And if you use that extra space created as your manifold, you may not even have to change any part of the bench and its duct work.

Bacon Lee wrote:

But my top is NOT 4 feet from the celeing with exposed wood frame. My green house is only 7 feet high, and the barrel alone already 3 feet. I think the top of barrel is only 3 feet away from the wood frame celeing.

And above the supporting exposed wood is the plastic roof of the green house?

I'm thinking I'd just screw a heat shield to the exposed wood framing (as shown on page 7 of that wood stove safety PDF - the brackets are attached to the exposed wood frame, and then the shield is attached to those brackets). A 4x4 foot metal shield (centered above the center of the barrel) ought to be sufficient, and surely anything larger would be as well. Some folks have used corrugated roofing panels for their heat shielding.

Just keep your stove as low as is safe and practical.

And if you are moving the stove anyway, you can reconsider how to best protect the concrete floor too. A number of ideas were discussed a few days ago. That might be worth reviewing before your next build.

My goodness, Erik, reading all the works I have to do in your post already made me exhausted. I don't even know how to do a lot of thing which you address. If I buy airplane ticket for you, would you want to go to California to help me with this? I will have a travel log for you to stay too. But you get no pay, this call "helping each other out"

Bacon Lee wrote:
My goodness, Erik, reading all the works I have to do in your post already made me exhausted. I don't even know how to do a lot of thing which you address. If I buy airplane ticket for you, would you want to go to California to help me with this? I will have a travel log for you to stay too. But you get no pay, this call "helping each other out"

Sadly, I am still a wage slave. I do not presently have the financial freedom to take the time off work. But maybe one of the others would be able to?

But, I think the only new thing, is learning to install the heat shield. That's relatively straight forward. 29-gauge metal (or thicker), and some brackets. Fasten them to the wall. (Page 7 of that PDF provides an illustration.)

The only other new stuff, is knowing how far to space the barrel from the wall and ceiling. I'll attach a few jpegs I found somewhere (I've forgotten where)...

...and here's a couple on the spacers...

Everyone else is busy. They don't even have time to give advise, how do they have time to help me. I will check with the Winser to go down here in CA to help me. I wonder how much they will charge me and see if I have money to pay.

The table showing how much you can reduce the spacing, boils down to two variables:

1. Do you have a non-combustable covering material?

2. Is there a metal heat shield?


If there is a tile or brick shield, and it has at least a 7/8" air gap behind it, you can reduce the clearance by 50% (or half).

If there is a metal shield, and it has at least a 7/8" air gap behind it, you can reduce the clearance by 67% (or two-thirds).

In other words, it doesn't matter if the metal shield has a tile or brick facing. Brick or tile by itself reducing the safety clearance by half. And a metal shield reduces the safety clearance by 2/3, no matter whether it is also faced in tile or brick.

EDIT:

The above is for walls. Ceilings the reduction is less, basically because heat rises

Either 50% of 33% reduction of clearance, which is recommended as 5-feet (60-inches), so most of us, according to this piece of code (and it can vary from one county to the next), will need heat shielding on our ceilings. The metal shield is the easiest to make. And it will reduce ceiling safety clearance by 50%, so that 60-inches (5-feet) becomes 30-inches (2-1/2 feet).

Bacon Lee wrote:
Everyone else is busy. They don't even have time to give advise, how do they have time to help me. I will check with the Winser to go down here in CA to help me. I wonder how much they will charge me and see if I have money to pay.

http://www.ernieanderica.info/arrange-a-workshop

Back to square one, very sad!

Oh, I don't know. Better than burning your place down! Now's the time to catch critical errors, the sooner the better.