Rocket Mass Heater Dreaming

I've been dreaming about Rocket Mass Heaters recently. Mine won't happen until we redo the floor in the sitting room (which is on the list of things to do) so I'm just researching and dreaming at the moment. I was thinking about how multifunctional an Rocket Mass Bench can be and came up with the following sketch

How many uses can you spot, and what good ones did I miss?

I cut 1\3 of a drum and made a door in the side of it to make an oven that sits on top of the RMH's drum. I recommend it for anyone using a drum in their RMH.

#1 visual of a scheme that may be practical for us. It is totally imaginary at this point.
This is a 6 in / 150mm j type rocket with a radiant barrel. I liked the look of the compressor tank in this thread so have used a rounded top. I might be able to use a stainless hot water tank we rescued, but will have to check it for material thickness and leaks. Since the corner it is in is an exterior wall, I have put metal panels (maybe brass?) to reflect the heat back into the room and look cool. After I drew this I started to wonder whether we would do better to have the whole thing reflected end to end, with the radiant barrel adjacent to the kitchen door (the alcove on the right) but husband thinks that having hot barrel next to the passageway would be a problem even with a protective barrier/fence, and since we would be insulating the wall anyway the corner position would not be a problem.
We don't have clay here - maybe a tiny bit if you dig around some of the springs, but really not worth the effort. So I hope to use local basalt rock as the mass around a hollow bench. This may be supported by 2 half barrels, or brick with paving closers. I need to get a better idea of the bell sizing. I think the cross section of a half barrel is not really big enough to act as a stratification bell unless it is spaced off the floor by several inches, which would then compromise the comfort of the bench by being too high. The area between the sofa and the burn tunnel could be a brick bell and I have the idea that I could maybe optimise the size here by adding/removing extra courses. The other option we may have, is to go down into the floor a bit. We currently have a suspended floor, which we intend to infill and insulate, so there is maybe a few inches in height I could gain by going down (?! I hope that makes sense!). We may be able to use the existing sofa cushions (which is what I have drawn) but I'm not wedded to that, we may find a better use for the sofa, which does have life left in it. I've drawn a clean out at the end of the bench, but should I have one near the barrel too or will taking the barrel off be easier?
I need to do a cross section to work out how the flue will work in a bit more detail. We have an unused fireplace upstairs and my thought is to angle the flue into that. We generally have a good draught in our adjacent chimney (which was stolen through the wall from this room to serve the kitchen range) - usually too much due to the wind actually. I know the kitchen flue is a 6 inch, so am assuming we can get a similar size into the upstairs chimney and insulate with no issues. It may need to be a flexible pipe rather than solid though, so I wonder if that could hinder the draught?
I have some new firebricks which I bought to play at forges, which I may set up as a burn tunnel just to get my hands in. I know there isn't enough detail on sizing here to make a yea or nay possible, but have I missed something obvious?

Hi Nancy;
Overall, it looks perfect.
A few things I noticed.
Using a stainless water tank will look good, but ensure enough room between the riser and walls of the water tank.
If you use a five-minute riser it should fit just fine.

Sheet metal (brass) with 1" spacers is perfect wall protection and brass is rather good-looking as well.

About clay.  Are there pottery places nearby that may sell sacks of dry clay?
Away from extreme heat, any dry clay mixed with clean, consistent size sand (no rocks) makes a great mortar that is easy (but dirty) to work with.
Clay mortar is removable and reusable.  Concrete mortar is not.

It sounds like you will be able to utilize your upstairs chimney. Slight angles are ok but avoid any 90-degree bends.
Depending on the condition of your upper chimney you might be able to use it as is.
Remember the outgoing exhaust temps should be in the 150-200F range.
Flex pipe inserted thru could be a restriction but I doubt it.

As far as cleanouts, I think a second one located at the start of the bell will give you easy reach for any buildup of ash.
Although if using a vacuum cleaner the one on the end should be sufficient.
Unlike a piped mass a bell system can go years with no cleaning at all.

Oh my Gosh!!! You have fire bricks on hand and you have not built a practice J-tube rocket in your dooryard yet?
Your rocket scientist apprenticeship will last much longer than it should if you do not start getting your hands dirty!
♥♥   Have fun!

Thanks for the thoughts Thomas.
I’ve had a quick look at the stainless tank, and it would definitely be too small a diameter for a brick built riser. At about 18 inches diameter, it might fit a 5 minute riser as you suggest, athough I haven't checked the gauge yet. It would be so cool to find some furnace peephole glass and make a little window on the top of it to cast burner light on the ceiling and be like a giant radio valve….How would a rounded barrel top affect the gas flow? I imagine that the gap would have to be tuned to avoid the gas stalling at the top. The thread where I found the picture didn’t have follow up posts saying how well it burnt when the heater was finished.
I was also thinking about using clay mortar, at least for trial builds. Matt Walker has described how practical that can be. There is a pottery on Skye - great idea to ask them about sourcing clay thanks!- it might save me delivery charges. I guess normal building sand as one would use in a concrete mortar would be fine (easy to get from builders merchants)?
I gather a temperature probe in the chimney to measure the gas temperatures is a good idea whilst tuning the system.
The firebricks were technically bought for my husband to play at smelting (our rock is magnetic although only basalt so not particularly good ore) but I do think that a j-tube trial run might be necessary either outside (weather permitting), or possibly in the workshop if I can rig up a flue....
 
So more thinking and another sketch....
I'm assuming that for a 6 inch j tube system I can have about 3.5 sq m Internal Surface Area (ISA) of heat absorbant bell. (Glenn Herbert says 30 sq ft (=2.79 sq m) ISA here and Satamax says 4 sq m here)
I've been calculating cross sections excluding the 'table' area between sofa and firebox:
1) Excluding an insulated house wall a 2m sofa full profile gives an ISA of approximately .335+(.25+.5+.5+.3)x2=3.435 sq m so a bit much since it doesn’t include the table area
2) Sofa profile base only (including house wall) .38+(.25+.9+.25) x 2=3.18 sq m this looks like it could be feasible.
3) Sofa profile back only (excluding insulated house wall) .21+ (.3+.75)x2=2.31 sq m also looks feasible.
The table area could have an ISA between .4 sq m and .92 sq m (or more) depending on how big I make it.
My gut feeling is that #3 might be best. I like the idea of a taller bell so the gases have more height to stratify in. I can imagine a lean-to sofa creating a chimney effect behind the cushions, or just being a blocky stone bell without the sofa, so a bit more versatile with furnishings.

Nancy Reading wrote:How many uses can you spot, and what good ones did I miss?

source

Two:
Enjoying someone company
A place to read good permaculture books.

I like both drawings, especially the first one.

Whoa, I knew you were like an engineer or something, but your sketches are AWESOME.

L. Johnson wrote:Whoa, I knew you were like an engineer or something, but your sketches are AWESOME.

It's very kind of you to say so, but I know I'm just a doodler! I just find it helps to clarify my thoughts if I sketch it out. I do it all the time with garden planting schemes too. Of the sketches above the section is the only one drawn to scale, and it made me realise how much space there is in the back of the bench compared to the base.

Good morning Nancy;
By installing a bypass, you can exceed Peter's ISA numbers.
Once you have a good draft going, you can efficiently heat more mass.

a little more RMH info inspiration to add to your beautiful sketches Nancy


free heat cold plugs cold starts


permies.com/fr

thomas rubino wrote:Good morning Nancy;
By installing a bypass, you can exceed Peter's ISA numbers.
Once you have a good draft going, you can efficiently heat more mass.

Ah! Thanks Thomas. So I'd need a door into the flue from the top of the bell that could be closed off once the initial burn had stabilised? I'm not quite sure how tha might work on a curved pipe. I found your thread here:  

But I'm imagining my flue at the moment within the bell - exiting at the top,
So I think I would need something that looks a bit like this:

source
But with a manual lever through the bell somehow.
The alternative would be to move the flue nearer the burn tube outside the sofa bit and have a fitting like yours on the side of the bell. That would make the chimney less straightforwards - adding an extra kink to get inline with the chimney upstairs.

This is an easy-to-mail model.

...and coloured in

For people who are dreaming of installing a rmh in their homes, the Freaky Cheap Heat movie may be a great resource!  Especially at the $1 special that is being promoted during Paul's most recent Kickstarter. This is just a clip, but it gives you the thought process behind the decisions of design and that is really important since each rocket mass heater may be a little different. We all need to adjust the 'recipe' based on our unique situation.

I love this design.

I always figured if everything goes wrong, I'll migrate to (a country not telling anyone where) and build a yurt that is half filled with a secret RMH bed and cookstove.  This design looks like a great starting place.