Brick heat riser

Hi everyone! Have a question about a brick heat riser. Can I use ordinary brick or even pavers, using refractory mortar, then wrapped in rock wool? I was just reading the thread on using firebrick. I would prefer to use FB but my wife might kick me out of the house per the cost. I have access to regular bricks AND landscape pavers for free. Will these disintegrate?

Robert Hohulin wrote:Hi everyone! Have a question about a brick heat riser. Can I use ordinary brick or even pavers, using refractory mortar, then wrapped in rock wool? I was just reading the thread on using firebrick. I would prefer to use FB but my wife might kick me out of the house per the cost. I have access to regular bricks AND landscape pavers for free. Will these disintegrate?

Regular bricks will disintegrate! After a while. Pavers might explode.

Check this type of construction, it's cheap!



You can also use cob, clay with ashes, straw, manure, wood dust or chips etc!

Landscape pavers and bricks can be used for the mass.

Robert; Consider making a cast riser, using fireclay & perlite. Matt walker has a youtube page (broaudio "cast core part 2") there you will find instructions on using a 16 gal grease barrel as an outer form and a cardboard concrete form (sonitube) as an inner form .Mine is on its second season and its as good as the day I poured it !

Thanks for the heads up! Little disappointing though, having the free material and all. I was looking for the cheap route, but I'd rather not rebuild the riser for quite some time. I cast my combustion unit per Matt Walkers method with some tweeking. Instead of using the backer board for the form, I used osb, then built the outside form. I used 2:1:1 refractory/clay/vermiculite and professional grade fiber glass in a wet pour. I let it cure for 36 hours under a heat blanket and fired it up. It came out beautifully - not one crack. I even accidentally dropped it about 5 inches when doing the final placement - still no cracks. The downside is - refractory is EXPENSIVE. I'm lucky my wife didn't make me sleep in the barn next to it. Anyway, I went way over budget - hence the question. On a side note, I have 300 pounds of stoneware clay w/no grog or sand #480 that I got for free. Can I mix my own cob with this stuff? Thanks for the timely help!

Stoneware clay (or any potter's clay) will make superior cob. As you say it has no grog, you will definitely need to add sand. Get some mason's sand, probably 2-3 times as much as you have clay, or more. Do a bunch of test mixes to see what proportions work best.

By the way, it's kind of a moot point now, but you used way more of the expensive castable refractory for your core than you needed. It is recommended to use around 1 1/2" thickness. You can then surround it with several inches of cheap perlite-clay mix for superinsulation.

Thanks for the info, Glen! It was a valuable ( and expensive) lesson learned. The primary reason I I used more refractory was strength, but also because there's only 1 place in my area to get powdered clay and they rarely have it. I bought their only bag. I ordered the other online. Reasonable price, but by time I had it shipped, it was as expensive as refractory. It was only after I poured did I find the free clay. Won't make that mistake again! Thanks again for the help!

Quick question. Getting ready to cast my riser. Have my 16 gal. drum and an 8" sonotube and all the clay I'll need. Can anyone tell me about how much mix I'll need to do it all at once so I can have it ready to go? And do I cast it off to the side or on the core? Thanks for any help!

Robert; I cast mine to the side as its easier to pack your mixture in with it sitting on the floor. As far as how much mix, I recall using one bag of fireclay and maybe 1/2 of a 4 cubic ' bag of perlite. It has been two years ago now since i cast mine and I had extra clay & perlite on hand so I may have used more. One thing I recommend is leave your sonotube way long and cut it back only after you have the riser in place and the 55 gal barrel in place, This way you can compensate for working with a ruler & paper and working with cob ! I ended up taping a 10" section of sonotube to my original to gain the extra height that my riser needed to get a 2-2 1/2" gap at the top. Also I switched my mixture at the very top and went with more fireclay + sand & only a small amount of perlite.

Thanks Thomas for the info. One other question. Did you leave the 16 gal drum on permanently when you installed the riser? The drum I have is an oil barrel that is brand new from an oil change company. It has the "rings" like a 55 gal. drum. I doubt I'd be able to remove it. I'll wrap the barrel with rock wool. Do you think that affect performance or eventually damage the riser? Thanks again!

Robert; You don't need to do anything to the barrel other than burn off the paint before you cast it. I believe that I used my oxy/acd torch on flame thrower and burned the paint off quickly with it. I built a trash wood fire in my 55 barrel to burn the paint on it. No insulation is needed as your casting is the insulated part of the riser, the barrel is just a form. One nice thing about the barrel is its ability to be lifted off in the need of a rebuild of your core. I rebuilt my core this summer, and was able to lift off the riser,place it aside and the just set it back on the new core when ready... try that with any other riser!

I finally got the riser cast! So far it looks nice - let's see how we'll it performs. Will let it set overnight under a low heat blanket to firm up then place it tomorrow as long as my neighbor is available to help me move it. I actually went with with an 8" duct instead of the sonotube because of having to fire it up inside.

Robert; Looks really good ! Nothing wrong with a metal inner form. Could be the pictures, but it looked like your barrel has paint on it still ? Your build is looking great ! keep the pictures coming !

Sharp eye! Just a little at the bottom. Going to get it with a wire wheel now that the barrel has some "ballast". Thanks for the compliment! I hope it performs well too. Will keep pics coming. It means a lot to hear that from someone with experience!

Woo hoo! Finally placed the riser! I let cure under a heat blanket till this afternoon. Then finished cobbing the back half of the core in preparation for the riser. I laid a 2"x2" bead of cobb to create a good seal under the riser (maybe overkill), borrowed a neighbor to share in the fun (couple hundred pounds worth), placed it and leveled it and pushed it down to squeeze out the excess cobb seal. Then sealed the outside. Fired it up with small fire and..... That rockety sound! Now on to the barrel placement. What a process! Thanks to all for your help to this point!

Bump, so how is it performing?

Hi Jim, it's seems to be working well. Even cold, it lights up quickly with no smoke back. Draws like crazy and really roars! In reading a thread on barrel temps though, I'm a little concerned. The hottest I've been able to get it is 650 on the side, sustained at 450-500. Shouldn't it be getting much hotter? I'm getting white ash in the bell, very little black. When I fired it up the first several weeks, I had a good supply of hardwood millwork scraps and 2x4 scraps and it burned almost everything - almost no residual ash. When I ran out of that I had to buy wood, about a 1/2 face cord of black locust. It turns out that it was not as seasoned as the guy said- my bet no more than 7or 8 months. Fire was very anemic, barrel temps no higher than 300. Tried drying it out under a heat blanket for about a week and it helped some. Picked up some oak, walnut, cherry, and locust from another supplier. Drier, but probably still not dry enough. It was not until I started mixing in some 5 year old 2x4 scraps with the hardwood that I was able to achieve the higher temps. It still doesn't seem like I'm getting it nearly hot enough. It taking about 3-4 hour burns to even get the mass warm ( it's dry). I feel like I have a good build, but not getting the full benefit. Any thoughts? I'm including some pics.

450-500 sustained sounds right to me from everything I've been reading and I've been reading a lot. Probably 200 hours in the last few weeks. With that said I should say I've only built stoves up till now, no heaters. However, I'm just about to assemble my first proper rocket heater tonight. Temporarily to test my odd design. If it draws OK I'll be finishing it off tomorrow. I hope it works, knock on wood. I know how everyone likes to caution to build one to the book first, but what fun is that. LOL

That does look really good Robert. Any chance of getting a video of the burn?

it's insulate bloks

Thanks for the replies Landon, Shilo. Ever since I started using the native hardwood I've been having a lot of residual ash, to me indicating a less than complete burn. I'm hoping that its just a wood issue and that by next year my wood will be dry as tinder. Any thoughts on that? As far as the blocks are concerned,I'm not quite finished. I plan on pouring fast setting concrete in the blocks to eliminate the air gaps, just haven't got to it yet(almost out of clay). Here's video of a recent burn. I hope it plays. Let me know what you both think. Thanks!

Can we get detail of how your upper barrel attaches to the lower? I like the idea of covering the core like you have.

Chuck

Chuck, I'd be happy to. The idea for the barrel system came cometely from Ianto's book. I've found that it gave me a lot of flexibility with my build. Keep in mind, this is my first build, but I've had great success with it. To start you need two barrels, preferably with removable lids. Be accurate with your height measurements as to allow for the proper gap from riser to barrel top. Take the first barrel and turn it upside down:the bottom will now be the top, so the rim will match the bottom rim of the top barrel. Got that? Measure how much you'll need to cut out to fit over the core and for how much height you'll need. Mark it well on the barrel. Cut out the solid end of both barrels with a sawzall ( be very careful not cut through the outside of the barrels - I scrapped a couple doing that). Then take an angle grinder to smooth out what you couldn't get flush with the sawzall. You'll want a smooth drop for the hot gasses. Then cut out your markings. I would recommend having a second person steady it while you cut. In my case, I found that dismantling my chop saw and using it free hand with a masonry blade was much easier. Your cuts don't have to be super accurate because you can fill in any gaps with cob. Once you have the bottom barrel fitted, make your connection to the exhaust manifold. Make sure when you're measuring for height to allow for 2-3" of depth below the manifold to allow for a good ash pit. Seal the inner and outer barrel bottom with cob. Once that is securely in place, move on to the top barrel. Turn the top barrel upside down. Initially I used 1/2" fiberglass gasket rope w/incuded adhesive. Throw the adhesive away - it's worthless. It's rated at 1000* and after a few burns it hardened and flaked away leaving air leaks. I instead used high temp sealant caulk rated at 600* - it really seals well and remains pliable. Lay a thick bead on the rim that will meet up with the bottom barrel, lay out the rope gasket on the bead firmly, then cut the ends to size. I put a little extra sealant on the ends of the rope to make sure I had a good seal. Let it set up for a few hours. I also laid a bead of caulk on the rim of the bottom barrel too. Overkill maybe but I didn't want to do it again. Take the extra lid clamp ring and loosely place it over the bottom barrel. Once the caulk is set up, flip the barrel over and CAREFULLY lower it down over the riser, taking care not bump the riser. Once in place,adjust the alignment of the rims. It can tricky because the rope wants to roll. Install the clamp ring and tighten but don't overdo it. Then, when you're ready for the top lid, use the caulk to seal the bungs on the lid (if it has any) and lay a good bead of caulk under the lid rim(remove the rubber gasket that came on the lid first!) Lay out the rope firmly into the caulk just like you did on the barrel rims. Put the lid in place and tighten the clamp ring. You'll have very airtight barrel system. It's really easy to remove the lid to inspect, or to remove the top barrel for maintenance. I really hope that this helps. Let me know how it turns out!

Hello all what I have used as a heat riser is a 8 inch flue tile set on 2 layers of fire brick. It works but I would like to with something like a smaller size round flue tile 24 inch high surrounded with clay inside a 8 inch or 12 inch square flue tile. The problem I am having is getting the round flue tile. I am located in western Canada and cannot find anything here. I phoned places in Montana what is suppose to be the hot place for the rocket mass heater and no luck there either. I would have to practically have to go straight to the factory to pick up the round flue tile. Any thoughts on this would be appreciated you can email me at motkod@yahoo.ca. Thanks.

Hi Robert!  Welcome to Permies - Home of the top leading Rocket Scientists from around the World.

The clay tile you mentioned as a heat riser is not the best choice for longevity.
Since a heat riser needs to be insulated, the high heat held in will crack the tile from the fast thermal expansion and contraction rather quickly.
A simple way to begin is to use a perlite/clay mix stuffed between two pieces of stove pipe (one bigger than the other).
A firebrick stack is another.
The primo way would be to make a 5 minute riser - A stove pipe lined with ceramic fibre blanket.
Here's a link to a batch box version:
6 minute riser
Where abouts are you in western Canada?
I am near Kelowna and happen to have a roll of morgan superwool for sale if you are interested.
https://www.facebook.com/marketplace/item/344153337254840/