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rocket mass heaters

Morgan Super Wool for 5 minute riser, high or low density?

Benjamin Dinkel

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Location: Province of Granada, Andalucía, Spain

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posted 6 months ago

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Hey Rocket Scientists,
I found a website that seems to send Morgan Super Wool to Spain.
https://www.isotec-isolierungen.de/

I can choose between 13mm, 25mm, 38mm and 50mm thickness, I would go with 25mm (roughly 1").

Then I can choose between 96 kg/m³ and 128 kg/m³ density. Has anyone ordered some and can suggest a density to me?

Lower density should mean more insulation, but less strength...

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Fox James

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posted 6 months ago

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Where do you intend to use it?

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

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posted 6 months ago

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Making a “5-minute-riser” mainly. In all other applications (as in it doesn’t touch the flames in the hottest part) I think I can get away with rockwool which is about 1/4 the price.

thomas rubino

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posted 6 months ago

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Hi Ben;
I have used both but I always suggest the 8# density over the 6#, especially using it for a riser.
Are they offering Superwool Plus or Superwol HT?
I have not seen the "plus" version offered in a few years now, the HT has a higher temperature rating.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
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Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

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posted 6 months ago

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They're offering "Morgan TC Superwool Plus".
I'm just reading that it's only classified for 1200 C...

thomas rubino

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Posts: 6521

Location: latitude 47 N.W. montana zone 6A

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posted 6 months ago

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That is almost 2200F, more than enough for an RMH.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

166

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posted 6 months ago

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Perfect. I’ll go ahead and order a roll of the heavier one then. Thanks a bunch everyone

Mike Schofield

Posts: 52

posted 6 months ago

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I just checked the spec on this it says 'continuous maximum application temperature 1000°c'. I'm also thinking of using this in a 5 min riser would this be a problem?

thomas rubino

rocket scientist

Posts: 6521

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posted 6 months ago

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Hi Mike;
The short answer is yes, that will work fine.
You found the continuous rating for Superwool Plus at 1000C or 1832F
Superwool HT has a continuous rating of 1150C or 2102F
An RMH does not burn continuously, the short-term ratings are more applicable.
I can only get Superwool HT from my supplier now, Plus is not even offered anymore.
Plus has a rating of 2192F and HT has a rating of 2372F for short-term burning

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Mike Schofield

Posts: 52

posted 6 months ago

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The short answer works fine for me! Thanks I'll get some ordered.

Mike Schofield

Posts: 52

posted 6 months ago

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I was wondering how you got around the problem of sizing the correct flue size? I also am using Morgan superwool (25mm) for a 5 min riser however if I use 180mm flue I get internal dia of 155 and can only seem to find 150 or 160. Of course for the fire box and burn channel I can adjust the CSA. It's only the flue leaving the bell and entering the chimney that I am concerned about.. maybe this fine bring slightly oversized if I go with 160mm?

Mike Schofield

Posts: 52

posted 6 months ago

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Realised as soon as I sent this the ID will reduce by 50 not 25mm so therefore I'd need 200mm for riser flue leaving ID of 150mm (5.905512") slightly less than 6 but im guessing still acceptable?

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

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posted 6 months ago

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Hi mike.
I haven’t actually ordered any yet and haven’t experimented with it.
As far as I understood we would wrap the super wool around a pipe of the correct diameter, the same as our exhaust will be later. Then stabilize it with wire or rebar mesh. Then take the inner pipe out again.
You’re referring to the pipe that you want to have as an external layer? If you want to go down that path you could maybe cut one open length wise and make it a bit bigger or shorter.
But I would say 5mm of difference shouldn’t make a big difference. There’s going to be a part where the fire brick square part meets the round riser anyway.
Cob aka the permaculture duct tape!?

Mike Schofield

Posts: 52

posted 6 months ago

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Ah ok I misunderstood. I was under the impression that I would have oversized stove pipe that would serve as a permanent scaffold for the superwool. Permies duct tape - like it! I'm sure I'll be making liberal use of that!

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

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posted 6 months ago

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And I think I remember reading (or seeing in a video) that because it’s not 100% smooth inside you should compensate and make it actually a bit bigger than the CSA of your RMH. But maybe one of the senior rocket scientists can confirm that.

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

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posted 2 months ago

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I finally ordered a roll of the "Morgan Thermal Ceramics Superwool Plus", 25mm thick, with a density of 128 kg/m^3.
It's 4,46 m^2, 62 cm tall, so about 7 m long.
I also got some stainless wire from them. Including packaging to Spain from Germany it was around 100 €.

I went ahead and made a 20 minute riser for the cottage rocket I'm building.

Rolling off and cutting:

First round

Second round and wires in place. Another instance of measure twice, cut once. I used a 150mm exhaust pipe and some of the foil that came with the wool to make it slide off the pipe.
If it looks short to y'all, it's only 42 cm tall because it's for the cottage rocket.

Slid off easily, feels sturdy and looks good (apart from the second layer being a bit short...)

The inside with 4 bricks in the cottage rocket layout showing in the bottom to see how it will fit.

Benjamin Dinkel

Apprentice Rocket Scientist

Posts: 362

Location: Province of Granada, Andalucía, Spain

166

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posted 2 months ago

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Thanks to Uncle Mud and Tom I learned I only need 1" of Super Wool, not 2".
But in order for the material not to sag it should be held up by some type of mesh (rebar) or a metal tube.

I found an old bucket that was (almost) tall enough, cut off the top rim and the bottom and split it open. Next I took off the second layer of Super Wool from my "counting towards 30 minutes"-riser and put the 150 mm exhaust pipe back in, to keep it round on the inside.

I arranged the metal sheet so I would have a bit of the super wool sticking out at the bottom of the riser, to form a good seal with the burn tunnel. Some of it is also sticking out at the top, because the bucket was a bit short. If I were to buy some material, or find a bigger piece, I would have gone for an overhang only on one side.

Ratchets made it easy to wrap the "sheet" obtained from the bucket around the 5 minute riser. I secured everything with 4 sheet metal screws.

It was easy enough to get the inner pipe out. The outer pipe gives it nice stability. I'm happy with the result.

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