2 floor RMH

I am planning a 20 mm j-tube RMH to heat up 2 floors of 30 square meters each.

The burner and barrel will be situated downstairs with a cob bench and 3m duct. Then an insulated duct will go up to the first floor were a bench with 2m duct will be heating the first room of 15 square meters and a bench with 4m duct will heat up the second room of 15 square meters.
The house have high ceilings of average 3m10. (Second floor inclined ceiling from 2m50 to 3m70.
The walls are 50cm thick rocks.
Each room only 1 window and one door.
The second floor have a very bad insulated ceiling.

Anybody can give me some advice on the heat distribution so heat will be more or less equal in every room?
The lower floor will be the living room, I am not sure if 3m of (20mm) duct and the mass under the barrel will be enough to heat up 30 square meters (and 3m10 high).

Please any comments and thoughts welcome.

Hi Gert,  Welcome to the Rocket Mass Heaters Forum!

When you say 20mm, did you actually mean 200mm? ...which is close to an 8" system?
Otherwise, I think your stove may be a bit undersized.  :)

Its going to be hard to distribute the heat evenly in each room with your setup for several reasons:

1) Due to the fact that the exhaust gasses cool as they travel leaving very little heat left near the end of the bench  
2) The upper rooms will not benefit much from the instant heat experienced from the barrel in the basement.

However, if you have vents put in the upper floor, some of the heat will mingle its way upwards helping to heat the upper rooms.

Your total horizontal run is about 30 feet which is not too bad for an 8" system but unless your system has naturally good draft, you will have no way to prime it (unless you put a priming port in the upstairs pipe which is not going to be convenient). Also installing a heater downstairs can sometimes be harder to overcome the second floor draft but is certainly not a show stopper. Several people have posted here on the forums where they have had good success with downstairs installations....each house is different.

Another thought:  Is there a way you could position your downstairs core to be closer to the centre of the room with only a small bench, then have a pipe (or bell) travel up through the ceiling where it could then be very close to the upper level dividing wall and have a bell or bench on each side? The chimney would then also be very close to the peak of the roof where the cost of insulated chimney would be reduced significantly.

You probably don't want to tear down your house and rebuild it around the heater, but what Gerry is saying sounds a lot like heater in this cool video from Russia:

Thanks a lot for the answer Gerry, and indeed it is a 200mm, 8" RMH.

First of all, the reason I put the outlet chimney in that corner is that in that spot is already a bricked chimney upon the roof.

As you mentioned, the lower floor, or living room, better a short bench, but what is short? Will the first 3 m duct be enough, too few, or to much, to heat up the 30 square meter livingroom ?

Do you think, the fact that I want to split up the bench in 2 floors, will have a negative effect on the draft of the whole system?
I can not find on the internet (or this forum) any examples where people divide the bench over two floors.
Anybody experience with this?
Or were can I find some examples?

Any comments welcome....

An important consideration for advice is the structure of your house. Is there a basement below the lower floor, or is it on grade? How strong are the floors? Which way do the floor joists run relative to the bench you are considering? If the joists are perpendicular to the bench, the load can be spread over many joists; if they are parallel to the bench, a few joists have to carry the whole load, which is not likely to be safe.

I second the idea of having only a short bench on the main floor, and a masonry bell rising up through the floor and exposed to both upstairs rooms. As long as you can make a solid foundation under the bell, you won't have to worry about overloading floor joists in several areas. I think this would allow you to more easily fine-tune the heat output to the different rooms. If one gets more heat than the others, add some mass thickness there and heat transfer will be slowed to that room. You would not have a long path for flue gases but a short one with little drag. With an existing chimney at the side of the house, expense there is irrelevant.

I would run the exhaust from the bell up from the lower floor level along the ceiling of the lower floor to the chimney, positioning the bell and combustion core closer to that side of the house to minimize the distance. You could then make a bypass from nearer the top of the bell to the chimney pipe for easier starting if needed.

Another bell possibility would be making one bell on the lower floor, with a plunger tube exhaust rising to a second bell on the upper floor. Raising or lowering the bottom of the plunger would adjust the proportion of heat that is kept in the lower floor, with the balance going to the upper floor. It would need piers to support the upper bell, but not as many floor joists would need to be cut away as to clear a full-height bell.

For two storeys.

There is one in Canada, double bell on two floors. But no pictures anymore.  It's somewhere on donkey's site. But it's been so long since I have seen it. That I can't even remember the title 😁

I'm digging.

https://donkey32.proboards.com/thread/1330/story-bells-20cm-batch-proposal

https://donkey32.proboards.com/thread/3572/batch-masonry-stove-water-exchanger

Found it! And the pictures are back!

https://donkey32.proboards.com/thread/1973/8-215mm-double-bells-built

Have a look at this one: https://www.facebook.com/BatchRocketPT/ You need to scroll down a bit.
Of course these bells could be on top of each other but not necessary so. The lower bell is equipped with two exhaust  openings. The lower one is connected via a box to the main bell and is open all the time. The other one is higher up, sporting a bypass valve. This way, there is some degree of control what sequence is used: all of the main bell and top bell second OR 1/3 of the main bell and top bell second.

Thank you all for the replys.

All of you are giving ideas for making the thermal mass with bells, for sure a good idea.

But for several reasons I wanted to make a rmh in the traditional barrel-bench configuration. The main reason is that it can be build by people with less skills and experience. I am convinced a RMH with barrel and bench cost also less money and less time to build.
The horizontal bench makes it also possible to connect it to an existing brick chimney, so also a money saving aspect. Also the weight distribution on the second floor is in this particular case much more obvious with a bench.
And of course, these warm benches are so nice to sit and relax on.

But I am not going to start it building before I am sure that this system will work.

Really nobody have made or seen a system with a bench (and not a bell) separated on two different floors (like the image)?

Not sure how to link to a post so here is the permies url.  Jasmine Maurer seems to have built what you are describing, but she only posted twice here.

Well, That's about 8 meters. Or thereabouts.  That should be doable with a 6 incher batch or 8 incher J tube. I would advise for the Batch. J tubes are way to fiddly for real life use in my opinion. In that kind of layout, you can go for more than 50 feet of horizontal flue. Elbows are negated by the two vertical runs. May be eve, better would be to do half barrel bell benches. A bypass to only the top bench would be clever, for startups. But i can't see why it wouldn't be doable. HTH. Max.  

Here is the thread that Nancy found.
https://permies.com/t/23699/dual-benches

Bells don't have to be vertical. As Max says, half barrel bell benches would give the features of a bell and of a bench. It could be a bit lighter for less stress on the floor joists. You need to know how the joists run relative to the proposed bench location before you can know that it will be safe to do. The joists will ideally run perpendicular to the bench.