Rocket Mass Heater

Hey all!

I am planing to build my first rocket mass heater and I thought I upload the plans, questions and eventually the build, knowing there are very experienced people here,
I´m hoping you could help me through it.
I live in Athens, Greece. I´m on the 6th floor of an 8 floor building and it can get cold here. it´s an 85sqm open space. the building is industrial so it can hold the load and     It´ll be placed mostly above a beam.

My first question is if I should do a 6" or 8" system. the 6" (15cm is wildly available here but the 8" seems hard to find and more expansive. All the explanations I find are for the 8" and the space is large. Just making sure, it´s better to insist on the 8"?
2. I cannot put a chimney through the building so it´ll go out through the west side wall, then maybe 4m horizontally (I´ll add upward slope) and then two floors up. this part would have to be insulated, right? would foam/rockwool with some silver tape around it be ok? The insulated pipes I found online are real expansive... anybody has experience with that?
3. I´m pretty scared to install this chimney by myself. I spouse professionals could do that?
4. For the heat riser, I see people use ceramic blanket. Could I use rockwool/ perlite slip or better just order some blanket already?

An 8" system will certainly be more capable of ensuring you get enough heat. But a 6" might be fine, depending on conditions. 85 square meters is around 850 square feet, not large by US standards, and you will have no ceiling heat loss. How much wall exposure do you have, and what kind of construction is it? Any south exposure? North exposure? You say "cold"; how cold is it? What is common winter day high and low temperature? With this information, we can give better advice on 6" or 8".

The 4 meter external horizontal chimney run is problematic. Can you make any of that run inside your own space? It would both improve the heating and increase the draft. I presume you can't get a closer location for the vertical chimney. Homemade chimney insulation can be effective, but may be against building code. What kind of regulations do you have? In your high location, I would use materials that will for sure not have to be repaired or replaced in a few years.

Pieter,

Athens is rather a warm place in winter.
Is your building insulated?
Is the 85 m2 open space or it has rooms? If yes, are they separated with masonry walls or something lighter?

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.

Athens dosn´t get bellow 0 Celsius but actually can get pretty cold inside the buildings because they are not really designed to deal with that.. My place in one space (expat the bathroom so the room is actually more like 70sqm) It´s brick walls and terrazzo floors that turn into a freezer in winter.  my apt in the center of Athens is built in 1965. Its 6 floors of factory spaces and the other two floors are apartments. It used to be a typography factory and some other floors still got those massive pressing machines so I´m less worried about the weight.
My walls are not insulated and the wall exposure is north west and east with very large windows on the west and east  (I´m planning on double glazing them as first part as this winter project). It´s also get extremely hot due to this orientation. The chimney would go on the west side where I have afternoon sun at most days and because of that, I also thought of using the chimney as a solar chimney in summer : make a opening/ cleaning port at the part of the chimney that's inside the house and close to the ceiling to open and draw the warm air out in summer...  Maybe it could be even better without insulation for this reason? If it´ll be isolated I guess I cannot do that.

I can´t run the chimney inside the above properties. The part that would run vertically, I also prefer outside but maybe I´ll compromise if it is very important. Can you tell me why this is an issue? I´ll also mention that above the part of the chimney that would run horizontally, there's a balcony of the floor above so It might add insulation. I am honestly most worried about it not having a good draft.

About regulations.. I lived in Germany before moving here. I am not sure if  it´ll be completely legal. I´m not going to try to get a permit.. I live in a yet very rundown area of Athens and from my window I can see countless building violations.. Also a few of my neighbors has a fireplace. I doubt if its with any permit... I thought best is to locate it above the beam and keep size to minimum.

I´ll add a floor plan of the placement I had in mind. measurements are in cm.

As you control the whole interior leading to the chimney location, I see no reason not to run the exhaust inside just below the ceiling right up to that corner. I also think that if you do that, the mass run can be reduced a little bit so the exit temperature is higher, and then get some radiant heat from the whole length of interior exhaust duct. This would allow for not depending on rising right next to the barrel to regain heat/draft; you could run the exhaust up near the wall so it has a straight run to the corner.

I understand keeping the mass over a main beam in the floor, but if you want a low bench mass rather than a tall bell, it will be spread out enough to not matter much where you put it in an industrial-grade building. In a climate that seldom gets much below freezing, I don't think you need a large mass. If you actually want a bench rather than a tall mass, I would advise making a half-barrel bell (or other construction that equals at least a 20x40cm internal cross section). This will reduce the mass while giving the same radiating surface in the living space, and also greatly reduce the friction in the system so that draft will be easier.

You really want to minimize bends in the horizontal exhaust, so if you can rise from the mass, run straight toward the corner, then exit through the wall at a 45 degree angle that leads directly to the vertical chimney location, you will get the most reliable draft.

Man, I thought it´ll be straightforward but there's some considerations to put in it
I looked again at how I want to set it up and I realized there's some site restrictions and I might have to do it with the insulated pipe running outside anyway because I have a concrete beam running all through above my windows and there's a column running up on the same line with the heater so I think there's only two places I can drill a hole for the chimney ( I marked it on the photo)

I thought I reduce the size of the mass to 140cm from the bell to the end of the bench and insulate the outside chimney, give the 4 meter vertical part a good 70cm slope+ the pipe would be black (It´s a sunny spot  from 15:00 and in Athens its sunny even on most cold days)
Glenn, I looked at some half barrel. it´s like a stratification chamber? It looks really interesting but I really wanted to do a simple design for my first heater..
I would like to have just a low bench.
What do you guys think- would this size of mass be ok to keep the smoke warm enough on the way out? Would going for the 8" system be the right way in this case?

Should I rise the pipe near the bell? If not, how? I thought I can put the last part of the pipe above the first part so that it can heat up a bit. would that help or just have the pipe zigzag instead of do a 180

I´ll add a few sketches of those options let me know if they make seance..