First rough test rocket bell heater

Hello all,
I recently purchased about 100 firebricks for a buck a piece. I got some dense heavy bricks and also the insulated lightweight bricks. I put the bricks into a j tube and no problem, it drafted good and burned pretty clean. Now I set up more bricks around the j tube trying to make a single bell. I didn't use anything to make any part of this rocket bell airtight because I'm just testing it out outside. As soon as I capped off the top of the bell around the j tube the draft dropped dramatically. My j tube was made of the light insulated firebricks. I had a gap at the bottom of the bell where a flue pipe would go. When the top is capped the smoke would seep out of all the cracks between bricks. Again this is just a j tube with a brick bell laid around it. I believe I had enough area for the smoke to flow in the bell (a couple inches on each side of j tube). I am just worried that once I build it in my basement it will do the same thing and lose the draft. I do have an 18' chimney from my basement. Would this fix the drafting problem? In the test run outside I didn't actually have any pipe in the bottom of the bell. Just a space where it would go and barely any smoke made it out down that far. Is the insulated lightweight firebrick alone enough to make a riser out of? Also, not once when I was testing my j tube did I get flames in the stack. No reburn in the j tube. Would this be caused by air leaks from not having it sealed with mortar?

Thanks
Dave

Dave Marth : If 'Luck is having a simple solution to your problem then you are very lucky indeed ! Repeat after me when the Heat riser gets covered
you must have a Vertical Chimney ! Whether you use a barrel, or cover your heat riser with bricks, or an old Heat plenum off of a forced air furnace
or a capped length of road culvert, You most immediately make up a vertical chimney, at least before you make your next Rocket Mass Heater RMH
fire !

I am going to assume that you have a new edition of '' The Book '' Rocket Mass Heaters by Ianto Evans, Cobcottage.com, If not, that
might be your next step. As an investment, "The Book'' will save you Time , Money and frustration, and when you come back here to Permies you will
know you will be using the same words to describe the size, shape and orientation of each part to itself and each other !

I am much more concerned about your choice to place your RMH down in your basement, but lets take care of some paperwork and see how that
helps! look at the space directly below your name and then L@@K at mine ! At the top of your page just under the Permies banner of the week is the
Permies Toolbox, In Your Toolbox locate the '' My Profile '' Icon and click on this will take you to a page where you can add enough information
to allow your Fellow Members to give you better answers relating to your location. Who knows, it may help you find a near neighbor with RMH or Cob
making experience !

While you are learning to navigate Your Toolbox please consider using the Search function, this will connect you to do a Google Search of the Web or
an internal search within the files of every forum topic ever posted to Permies.com.

Simply enter a brief search topic, and where it says search forum(s) select All available then just set your choice searching the Web or Permies
Membership has its privileges, you can come here 24 / 7 to use this function !

To understand Some of the problems you can incur by selecting a basement location for your Rocket Mass Heater RMH, please do a search for
'Stack effect' and for 'whole house stack effect' also take the time to check for your fellow members comments on RMHs in basements and note how
few report success with their trials !

To get the maximum efficiencies out of our RMH we need to be burning small finely split very dry wood, this works very well when the RMH is crafted
to be a fine piece of built-in furniture and is given Pride of Place in the Heart of the home. When placed within an easy arms reach of the homeowners
daily tasks having a Rocket Mass Heater is like having a healthy Bank Account into which you make small timely deposits of wood and receive regular
Dividends in the form of heat, Deep comforting, bone warming heat ! AS homeowner you quickly learn to fead and adjust your RMH by ear, tending it
with no more thought than adjusting a pair of glasses !

Having an RMH in a remote location prevents you from having the sight and sound clues that make feeding your rocket the perfectly timed work of an
instant, leaving you arriving at your rmh continually early or late, and causing you to periodically interrupt your tasks to go check on and tend your
RMH, this will quickly grow to seem endless and a true Drudges task, begrudged, and cause you to look for excuses to avoid tending your heater !

Your Rocket Mass Heater will only serve you as well as you serve it !

After your research please come back here with any more questions, many successful Rocket Mass Heaters were started by members here at permits
some of our members have extensive experience with more than their 1st rocket mass heater ! For the good of the craft !

Think like fire, flow like a gas, don't be the Marshmallow, As always, your comments,and questions are solicited and are Welcome ! Big AL

Insulating firebricks good

2 inch gap, a bit small in my opinion, wether it is on top or on th esides. The rough bricks make a hell of lot of friction.

When the barrel goes on top, the chimney goes up, as Allan said. Even a temporary one for testing purposes.

Be carefull with your transition between bell to flue. Usualy we say it needs to be 3 times as large as the CSA.

For your heat riser you want to keep it as hot inside as possible, thus insulating firebrick would work better in this position than hard firebrick. There might be issues of durability that would negate this, it probably depends on exactly what kind/quality of bricks you got and their condition (used already?)

The bell wants to have high mass and decent thermal conductance, thus the hard bricks would definitely be better there. Soft firebricks have low mass and low conductance.

Dave and Glenn : Last December I tried to weigh-in on what I thought I knew about where and when to use each type of Fire brick In a Forum Thread

'Fake Fire Brick'' In the Rocket Stoves Forum here at Permies.com.

Because my thinking contained some minor errors I am going to point you to Erica Wisner's answering thread/response near the end of that post.

This is a simple google search within Permies.com. Erica and Ernie Wisner are both our moderators here at the Rocket and Wood Stove forums !

It is a quite lengthy thread but worth reading to get the straight facts! Basically insulating materials need to be saved to place completely around
Dense Fire brick that make up the combustion core, included with this is the Heat Riser ! For the good of the Craft ! Big AL

I just happen to have that most excellent info. thread bookmarked:

https://permies.com/t/30551/rocket-stoves/Fake-fire-brick#299460

Byron C. : Thank you, not my proudest moment but Like I sign off- For the Good of The Craft ! Big AL

Thanks for all the responses. I am almost done with the rocket stove book now and will ask remaining questions when I'm through it.

Thanks again for your help and pointers.

Dave

Thanks for the pointer to Erica's comments, Al. Proof that nothing beats long experience So the upshot is that a purely insulated combustion zone will indeed increase early combustion efficiency, but at the cost of long-cycle effectiveness. Good things to take into account as I build my system (and plan for friends' systems).

Glenn H. : because the denser 'Firebrick' has more thermal mass, it will still be hot enough to make re-liteing a RMHs fire in a twice daily burn cycle easy.

It will also continue to thermo-syphone the last of its heat slowly to the barrel and Thermal Mass , a good thing and an end of cycle thing! A hot Heat Riser
will also make operations easier ! Also dense fire brick directly under the feed tube will last longer due to jars, scrapes, and dropped log-ends !

But- ? I missed your point/comment on Long - cycle effectiveness ? Can you clarify a little more ? for the Crafts ! Big AL

Late Note : can you make a new topic or go back to Fake fire brick ? we do not want to hi-jack Daves Topic ! A.L.

Long-cycle effectiveness = shorthand for exactly what you said

Glenn : But, but - I don't see a downside ! Big Al

Okay, I have to be more verbose... repeating more of Erica's content.
A combustion zone made of just insulating refractory will heat faster than a dense refractory combustion zone, but won't hold the heat as well at the end of the burn. Thus a dense core with insulation around it gives the best overall performance, both thermally and structurally (abrasion/erosion resistance).

I have been calling everywhere and can not get my hands on any fire clay. I called lowes and home Depot and they both don't sell it and pottery places around me don't sell it either. It's really expensive online to buy and ship it. Anyone know of a good source to buy the fire clay to make castings with?

Dave; I went to three building supply's before finding the one that had (or even knew what it was) fireclay on hand ! Keep calling around , somebody will have it. Most places wanted to sell me mortar mix. I traveled 65 miles each way and paid 18.00 a bag , not cheap but well worth it ! Later I discovered that a small building supply only 15 miles away, Stocks It ! and its 13.00 a bag ! Been buying my fireclay there ever since.

Fire clay:

Lowes doesn't call it fire clay but home depot does, according to these relevant links:

http://www.lowes.com/pd_10367-13040-10367_?productId=3110273&site=shopLocal&utm_campaign=bazaarvoice&utm_medium=SearchVoice&utm_source=AskAndAnswer&utm_content=Default

http://www.homedepot.com/p/H-C-Muddox-50-lb-Fire-Clay-100011882/100321936#.UoMGgPnXTrI

Home depot had it on line ,but only sell it back east !!! wouldn't put any on a truck to sandpoint. I didn't have any luck with loews either. The building supplys that did have it were carrying it for local stone masons.

I think I figured out what to do about my clay situation. I found cat litter that is 100 percent dried clay. I believe that will be good enough to substitute for fire clay if I mix with perlite and fiberglass and some high temp mortar mix. What I was wondering is if I make the whole combustion chamber and riser out of bricks, then spread a 1 inch layer of the clay perlite mix on all the internal surfaces of the setup, would that be as good as using vermiculite board or insulating fire brick? Would the clay break off the brick surfaces after it heats and cools? I hope this works since it seems way easier than making a form to make a casting. I am going to try the batch box version.

My other option was build the whole burn chamber and riser out of vermiculite board.

What sounds better to use guys?

Dave, stay with tried and true setups.

Firebrick splits are cheap enough. You hold theses in the proper shape one way or another, then insulate with "rockwool" on the outside. That is a sure way to make it work.

I only have a few insulated firebrick and then I have about 140 heavy dense firebrick that measure 6x9x2. My fear is if I just use heavy firebrick it will take too long to get hot enough to reburn everything. The insulated firebrick is pretty expensive that I've seen. Has anyone had luck with the dense firebrick for fire box and riser with insulation on outside?

Like I said my only concern is time it will take to get up to temperature.

Thanks again

Glenn : Sorry I was reading your comment about long-cycle effectiveness as a negative, you have made it perfectly clear that that error was all in my head !

Dave : Not a problem, any unburned gases will be vented outside to the environment by the rockets strong draft ! At 600 degrees,( less than the temperature
of a lit cigarette) you will already be burning the middle range of wood gases, the ones that make creosote, and they will burn at a rate hot enough to burn
everything !

Remember Time, Temperature and Turbulence, From the start of the book ! Before things get really hot you have time for the turbulence to take up the slack !

"Has anyone had luck with the dense firebrick for fire box and riser with insulation on outside? "

That is the standard recommended method. Splits (which are 1 1/4" thick) would give less mass and quicker heating by a bit, but probably not enough to be worth buying if you already have a stock of 2" thick ones. You could do the perlite/clay insulating wrap for areas where you do not have enough insulating brick.

Dave, heavy dense firebricks is what was used at the begining of rocket mass heaters, and then the insulation was lousy! And they worked, may be not testo sniffing performance, but well enough.

What i would advise, is to make the firebox (are you going batch or J? ) with the bricks on their edge. And the same for the heat riser. Carving lips and holding theses with wire and packed insulation into a metal pipe is my prefered method. Cheap, no skill way.

My latest way, for cheap and easy is flue elements. But i live on the italian border, and not everybody can find that stuff.

http://donkey32.proboards.com/post/11503/thread

Dave M. : Sorry, sorry sorry ! I just now noticed that you are considering trying to use kitty liter for your clay ! This stuff is a very poor grade of clay
and should not be used, I do not know of anyone who has tried kitty liter and is happy with it ! In fact I challenge any one here at Permies to tell me
that they used kitty litter and found a way to keep the cob made from it from cracking and turning back to dust , -that tracked all over !

Again I just now noticed your comment, and I am positive you will be dissatisfied with the result ! For the Good of the Crafts ! Big AL

Satamax,
Not sure what you meant by this paragraph.


"Dave, heavy dense firebricks is what was used at the begining of rocket mass heaters, and then the insulation was lousy! And they worked, may be not testo sniffing performance, but well enough."

What do you mean the insulation was lousy?

And Big Al, no problem, glad you caught that though. I may just drop the whole burn box in another box of perlite. I'll still brainstorm insulating the riser firebricks.

Dave Marth : the cheapest and easiest way to wrap insulation around the outside of the Heat riser is to use Rockwool, sold under various names at Lowes,
or Home Depot and use chicken wire or hardware cloth to hold it in place no worries 2 - 3 heating seasons ! big AL

dave marth wrote:Satamax,
Not sure what you meant by this paragraph.


"Dave, heavy dense firebricks is what was used at the begining of rocket mass heaters, and then the insulation was lousy! And they worked, may be not testo sniffing performance, but well enough."

What do you mean the insulation was lousy?

And Big Al, no problem, glad you caught that though. I may just drop the whole burn box in another box of perlite. I'll still brainstorm insulating the riser firebricks.

Well, plain cob isn't the best insulation ever to make a rocket core. Daub is a bit better. Then came in the perlite and vermiculite mixes. Now some use stuff like kaowool. Even cast riser out of kaowool and clay slip, or another binder, then surounded by more kaowool. I like rockwool myself. As it's real common in france, cheap, and can be found in skips

I can't find fire clay ANYWHERE for a reasonable price. Pottery store near me said they sell one pound bags for too much money. I live in eastern pennsylvania. Anyone know where to get it around there? Or is there an alternative recipe for making a casting of the riser excluding store bought castable refractory?

May be ask dem!

http://www.houzz.com/pro/shedddesigns/john-shedd-designs

http://www.houzz.com/pro/moveout/clay-born-pottery



Or buy tube?

http://superiorclay.com/fireplace-firebox-design/clay-flue-liners/

I heard terracotta chimney liner can Crack easily with the heat. How about the recipe of 4:1 perlite to furnace cement? Anyone ever try that formula?

dave marth wrote:I heard terracotta chimney liner can Crack easily with the heat. How about the recipe of 4:1 perlite to furnace cement? Anyone ever try that formula?

Clay flue liners work for me. Crack once, and then that's it! Tho, the landini ones i get are made with chamotte, and now out of production.

http://www.theceramicshop.com/store/search.asp

I think I finally found fire clay near me for a lot of money though. Anyway there are so many kinds and I'm not sure which one, they have high fire, low fire and other kinds. Can anyone suggest a product from that site to me? Also, does anyone know the volume of 50lbs of fire clay? I'm trying to find out how much material I need for the volume of a heat riser mold.

My riser I will make will be 8 inch inside diameter and three inches thick of fire clay perlite recipe.

Dave M. They should ether have lincoln 60 or know its equivalency ! Sorry I Cant help on the volume as We have good local clay ! Big AL

If I buy big hunk of wet potters clay would that be just as well? Is there a certain type I Should look for? I'm striking out everywhere. Otherwise can you recommend a recipe leaving out clay?

Ready made potters clay will work just fine, once it is softened up for making cob (i.e. combining with masons sand).

At the source for potters clay, you might ask them about buying it in bagged powder form so you can mix up your own. I find mixing my own easier (less time consuming) than softening "ready to use" wet potters clay.

I JUST FOUND A FIRE CLAY SUPPLIER!! BEST DAY EVER!

But it's $22/50lb.

O well at least I found it

And they are only 15 minutes away

If I cast a riser 50" tall 3 inches thick would it be strong enough to support itself or does that seem to large for a casting? Should I cast it in a couple sections then join later or would that make it more brittle?

Dave; I cast my 8" riser using a fireclay/perlite mix , with a 16 gal grease barrel as the outer form and a section of 8" cardboard concrete form as the inner form. The inner form burns off with the first fire leaving a smooth bore 3" thick insulated riser. I used one bag (50#) of fireclay , a small amount of powdered refractory and added perlite & water to get the right consistency . Your going for the insulative value with this mix so you gain a lot of your volume with the perlite. I would buy 2 bags of fireclay & one 4' bag of perlite and you will have more than enough. As far as finding a building supply that has fireclay, you may need to expand your search area. Living out west i think in terms of how many hours drive to get what i want , for me thats one hour to the nearest stop light and over 2 hours to any bigger city . You mentioned eastern penn. as your location , there has to be some hiding not to far from you , lancaster ? Philly ? keep calling, looking on line did not work at all for me. Ask for lincoln 60 fireclay its the most common ,although there are other names , at the most, it should cost $10 -20 a 50# bag / perlite runs around $20 a 4 cubic foot bag at a nursery/landscaping supply.

Dave; Congrats you found it ! No 50" is not to tall if your using a barrel as your outer form . Mine is 45" tall and extends above the outer barrel, but with the inner form in place you taper your chimney as it comes up. At the top mine is maybe 1.5" thick. After using my perlite mix to the top , I mixed up straight fireclay and sand to seal / coat the exposed perlite mix.

Thanks for your replies. Very helpful, everyone. Does It seem to risky to build an 8 inch system batch box rocket bell heater with a 6 inch 18' vertical insulated flu? Is there a formula I could figure out for the max exhaust temperature to run from 8 inch to 6?