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Post by travis on May 22, 2019 2:38:32 GMT -8
Has anyone out there used rock wool for a five minute riser? I can’t get ceramic fiber but found rock wool for a good price
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Post by Vortex on May 22, 2019 4:28:15 GMT -8
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Post by Karl L on May 22, 2019 5:19:52 GMT -8
I've used rock wool to insulate the walls of a normal wood stove - much lower temperatures than a heat riser - and it fell apart very quickly.
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Post by patamos on May 22, 2019 9:36:56 GMT -8
Here in PNW Canada we have products called 'Roxul' ranging from soft batts to very rigid 2" thick boards with good compressive strength. Tried making a riser with the latter a few years back. Quickly started softening and disintegrating. I've also mixed about 20% (by volume- not weight) of the softer batts into clay-sand plasters (as a way to add fibrous strength to single wall bells etc...) but the fibres are so short once blended with an egg beater drill that too high a proportion of this material weakens the plaster. Might be interesting to blend it up with sodium silicate though...
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Post by pinhead on May 23, 2019 7:58:35 GMT -8
Has anyone out there used rock wool for a five minute riser? I can’t get ceramic fiber but found rock wool for a good price Yes, I've tried. It was a colossal failure. With good, dry wood the rockwool won't last more than a hand-full of burns.
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Post by travis on May 26, 2019 5:24:19 GMT -8
Thanks guys good to know haha. It sounds like it would do for the outside of the firebox though
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Post by esbjornaneer on May 26, 2019 9:20:22 GMT -8
I used a 2cm thick rigid rock wool board/bat as insulation outside a 3-4cm thick heavy fire brick in my first rocket build. It was a BBR and I used several thicknesses of the board/bat. During the first burns there was a funny smell. When I dismantled it there was discolouration in places, not sure if it was outside the firebox or the inner 1 or 2 thicknesses at the base of the heat riser. It stayed in place as there were more layers still outside it (it is only the binder that burns not the fibers themselves) and an outer layer of bricks. Not sure if the insulation value is reduced when the binder burns. Good luck.
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Post by patamos on May 26, 2019 20:09:19 GMT -8
might make a good 2" sheets of insulation over top of a 2" thick cob pizza oven dome. Then 2" of cob over top of all that. 2", 2" and 2" are ideal for a 6" J or L rocket set up...
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Post by whazzatt on May 27, 2019 9:25:17 GMT -8
BOMBfire??? Glad you lived to tell the tale, Vortex!
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Post by Orange on May 30, 2019 21:17:17 GMT -8
I've used very light air-concrete for insulation because rockwool is unstable after 250C. It will crack but you can mortar it or surround with other materials.
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Post by dirtdevil on Sept 21, 2019 5:47:47 GMT -8
I have read that a square heat riser works better than a round one. Would it be better to just make a square metal tube and line that with a ceramic blanket or just go with the round one? This is for a J tube 6 inch heater.
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Post by peterberg on Sept 21, 2019 6:20:42 GMT -8
I have read that a square heat riser works better than a round one. Would it be better to just make a square metal tube and line that with a ceramic blanket or just go with the round one? This is for a J tube 6 inch heater. In my opinion, a square riser is comparable to a round one as long as the diameter of the circle is the same as one side of the square. A five minutes riser in a large stove pipe is waaay easier to do than in a square metal tube.
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Post by dirtdevil on Sept 21, 2019 14:24:16 GMT -8
Thanks. All things being equal I'll go that way then.
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Post by invention1 on Dec 11, 2020 6:31:46 GMT -8
Five minute riser has lasted through one year of experiments, then it was transferred to the permanent stove and has lasted through two heating seasons. Last spring when we shut the stove down for the summer I used a snorkel camera to look up into it, no apparent problems. This one is built as an 8" riser, using 10" Galvanized steel HVAC duct lined with 1" ceramic blanket insulation. The ceramic blanket is painted with Simwool Rigidizer www.simondstore.com/simwool-rigidizer-refractory-coating-for-ceramic-fiber-blanket-1-gallon.html and then sewn on to the steel duct using nichrome wire and ceramic tubes. The steel duct discolored a bit around the very top, other than that it is just fine. In the permanent stove the bottom of the steel duct is surrounded with masonry to trap it in place so it can't shift or have a leak where it touches the stove firebox. So this same 5 minute riser survived a year of experimental runs and two years of service with no degradation apparent. The sewn-on ceramic tube clips keep everything in place nicely. The rigidizer was overkill. I'd put together a kit of enough ceramic tubes and nichrome wire to build a 5 minute riser if someone tells me they are interested.
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Post by patamos on Dec 11, 2020 9:12:46 GMT -8
Just last week i opened up a L-feed rocket stove i had built for a tiny home the year prior. I had installed a 5-minute riser using 1/4" ceramic felt lining the inside of 5" dia. 26-guage metal ducting as part of a 4.5" system. The bottom 5" of the riser was in bad shape with the metal disintegrating and the ceramic felt sloughing off. Could be that the metal started going first and then turbulence etc battered the felt. The owner had been running the stove daily through October to April last year and then again this Fall, usually with 1 or 2 reloads. So it was getting pretty hot at the riser base.
Anyway, I replaced it all with I.F.B.s
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