Julian Adam

Hi Glenn, thanks for your input. Personally, I would be suprised if you are able to calculate the free flowing CSA, but not the circumference, especially since most of these areas are likely to be rectangular or a sum of rectangles. I do agree with you that it is good to have the 5 times CSA as a simple rule of thumb. At the same time, maybe it could kill a project for someone because of space restrictions, while there is a setup which could be acceptable in terms of friction, but without following the 5 times riser CSA rule.

Peter van den Berg wrote:
The bell could be deep and tall, no problem. Down to just wide enough to house the core, although in that case there should be at least a space at the back. Size of that space: at the bare minimum, 5 times the cross section area of the stove pipe, more being better. That space is there to lead the gases down to the bell exhaust.

Peter, I have been thinking about your requirement to have the section around the core where the gases pass at least 5 times riser CSA. You gave me the advice last year not to count narrow slits. Since then, I've discovered the 'hydraulic diameter', which I believe, covers the load better, when we are talking about friction through a section. Are you aware of this? If so, what is the reason you chose not to use it?
I have made a small comparison between hydraulic diameter and your expression in function of riser CSA.

For those wanting to skip to the conclusion: it seems encasing a core in a drum, produces a (roughly calculated) free section of 6.8 times the riser CSA, but only results in a hydraulic diameter of 175 mm. If we take this same hydraulic diameter, and assume the passageway is a rectangle behind the core (green), it would only need to be 340 x 117 mm2, which is a mere 2.27 times the riser CSA.

Curious to hear your or anyone elses take on this.

Leonardo Bevilacqua wrote: Hello everyone, this is Leonardo from North Italy.

Welcome! You will find many helpful people here! I'm also still constructing my first RMH, so experts may correct me or chime in.

Leonardo Bevilacqua wrote:
For the bell I thought about a stratification chamber made of concrete clinkers lined with firebricks in the upper part. I also thought of a double layered bell so that it would retain the heat longer.

Peter has proven this is possible with the pottery shop build which you probably have seen. I think it's a good idea. At least where I live, many people renovating their driveway give away these clinkers for free. You could copy where Peter applied his firebricks for some peace of mind. If you don't object the look, having the chimney outside the bell is more simple and more robust to execute. That being said, I will incorporate it into the bell myself, because I find it more aesthetically pleasing.

Leonardo Bevilacqua wrote:
Does this project sound good to you all? Is there anything that I'm not considering, or considering wrong? Do you think I could go on calculating and drawing a detailed design? Would such a heater heat the two rooms? Would it somehow heat a bit also the second floor?

Have you thought of putting it here:
In my opinion this is a better (more central) location of the house + putting the heater in a corner, facing exterior walls on 2/4 sides, is a bit of a shame I believe. You could use those corrugated sheeting which I believe Peter has behind the red heater in his house, inbetween the heater and the wall to transfer the radiant heat to convective heat, or at least pull it away from one exterior wall.
Drawing it out will never hurt in my opinion, I'd start with a top cross-section. The heater would also contribute to heating the upper rooms, in the way that heat always rises, but not in an active way. If you want that, you would have to continue the bell upstairs or make a second bell there. Personally, I would not invest in high-end firebricks for the bell (second-hand or cheap will be sufficient). But for the firebox, just buy new, decent dense firebricks and lay them with refractory mortar or with a tension frame and ceramic gasket (watch your lungs!)
Make the heater perform better: follow Peter's design meticulously. Allow for enough room for the gases to pass the core while cooling down. Insulate the chimney.

Good luck!

Cristobal Cristo wrote:
I'm just curious, how many bricks have you managed to bring total?

I've just counted from the image, there seem to be around 140 bricks. They are bigger than my other bricks, all 250 x 125 mm and some are 64, some are 50 mm thick. One big bonus added to that, is that there were additionally also 4 big slabs, which I will be able to use for the Shorty's firebox and riser's roofs (I have some castable refractory but was not looking forward to that) I'll post another picture of those tomorrow.

Something the man did mention, but which I probably underestimated, is that some of the bricks were contaminated with (light) fuel oil. In Belgium, some fuel oil had a red colorant added to it, for which reduced taxes applied. Many of the bricks have some of that red color, but don't strongly smell of fuel oil + seem dry. Some, however, were clearly soaked in fuel oil. Unsure what to do with it, I built a dry stack J-tube in the hope to burn off most of it.
3 burn videos on my YT channel:
https://youtube.com/shorts/z9melpBBixg?si=C1bzKGLxKHrWqtUf
I was pleasantly surprised with the J-tube performance as well, and of course every excuse to make a fire is a sound one...

In the end, I could see the bricks 'drying' up. Some smoke left on the outside, and I assume a lot was burnt by the J-tube from the inside. Will probably have to repeat to get the most of it out, but at least it was already having an effect.

Anyway, thanks to all of you for keeping this forum alive. It's refreshing and energizing to have all this knowledge open source, with everyone eager to share. Quite different from day to day work, I would say. Wishing you all a great (early) Christmas!

Just wanted to share I've been lucky this week. Although I think I may have enough firebricks for my core + inner skin already, I've still been keeping an eye out on the second hand apps for some scores.

End of last week, I stumbled upon a mountain of fire bricks - for free! And they seemed in quite good condition (better than the ones I already had - so less cutting!)

This was in the French-speaking part of Belgium, but I live close to the language border so only a 30 minute drive for me.

Once I arrived there I was welcomed by a friendly man in his late 50s. He was renovating a site which used to be a bakery - and told me the bricks came from the oven. He told me one guy spent a month, gave up, and finally it took 3 guys 5 days to take that beast down. Apparently more than 10 tonnes of mass.

The man said he was going to throw everything I didn't take into the skip, and since I only have access to a regular car, I had to make 2 round trips to avoid that of course.

One year later... Unfortunately without too much progress. But the renovation is moving along so I'm hoping I will be able to find the time to continue the build next summer. About the arches, I see I did not reply to you, Scott. As you may have noticed I can be quite a divergent thinker, and I really liked the appeal of using arches in my build + skipping steel & superwool. Realising how much more time it was (again) going to take, it looks like it's quite certain I'll be using some second hand steel window lintels I bought quite some time ago. They are extremely beefy (8 mm thick I believe), so I'm feeling confident they will hold up (indefinitely).

Incredible result, congratulations Peter & helpers! Are they topping it up all day long to have sufficient heat output? Almost a pity to cover it in clay plaster!

beautiful result, cedric, also an aesthetic improvement in my opinion!

Peter van den Berg wrote:
The ISA for the Shorty core is down to 85% of the recommendation for a first generation core.

That's what I thought, thanks for confirming Peter!

Peter van den Berg wrote:
Tried last month with the large heater in the Sculpter's shop  
and it works beautifully

I've been following your posts closely, wat een prachtige mammoet! Makes me a little sad I cannot find the time to finish my own. Looking forward to the rest of the sculpter build!