Benjamin Dinkel

Hi Colin,

the way I understand it you want high thermal mass and high conductivity around the tubes. The air flows through the tubes, exchanges heat with the tube and surrounding "dirt" and gets warmer (at night, in winter) or cooler (summer, midday). So you need material that absorbs and hold on to heat.
The condensation that you're talking about will happen when you cool down hot (moist) air and will happen inside the tubes, not in contact with the backfill. So I don't see why it shouldn't work with heavy clay. It might actually be your best material.

But maybe I'm misunderstanding the whole setup. GAHT didn't get me many results googleing.

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.

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!?

Hi Pjeter,
First things first I would check wether there is a safe and legal way to run that exhaust through (someone else’s?) part of the building.
Also it being 8 stories rings my alarm bells. In Germany (where I know the code better) things get very complicated in anything over 5 floors.
Asking a professional is a good first step as you mention.

Hi Kay,
A good starting point to all RMH research: https://permies.com/w/rmh-resources

Maybe check out the cottage rocket, an Uncle Mud design. It’s transportable and has some mass integrated. He built the first one for a school bus he lived in if I remember correctly.

And I second what Matt said. Without the mass you might be sweating while running the stove then freezing 30 mins after the fire goes out. An RV has almost no mass.

Unfortunately stopped at the moment. Postponed to probably January.
I’m trying to find someone in the area for a project this winter, ideally a public space which would serve as a good publicity.
If none of it works out I’ll spend my time building one or two cottage rockets.

Nicola,
I would go with 1:1,5:3 dimensions. Thomas caught a too long burn tunnel in my design (https://permies.com/t/263398/RMH-build#2616537).

So 10:15:30" would be a possible set of dimensions.
I can't see why it would not work.
The higher the riser, the more draft. But since yours goes into a bell and then out the chimney I don't suppose you need a whole lot of draft.

Maybe you can crunch the numbers a bit. A shorter feed allows a shorter riser. So making the feed 10” (25cm) instead of 12 let’s you drop the riser to 30”.
What’s the 8” space above the riser? Maybe you can make that a bit less too.
Also the insulation under the core you might reduce a bit.
Maybe saving 10” in total. 43” is still to high?

Hi Nicola,
if you can't put the core in the floor, why not raise the floor around the cook top?
Like a step that goes around the whole cook top that you can step on and do your cooking.