Mass bench fed directly by a modified sidewinder Shorty core

From 14 to 18 May the annual meeting of French mass stove builders was held in Montendre, organized by the AFPMA. I was one of the participants and for this occasion I cobbled up a workshop together with Oliver Kreuser from Terre des Feux. A large mass bench that had to be fed directly from the side by a Shorty sidewinder core. As a concept it was already an experiment but the exit of the core made it more complicated. Which was already facing to the side, was to be connected to the bench via a short tunnel. What the effect of this would be had not yet been tried, so I had no idea whether it would work.

A week or two before the meeting Adiel Shnior, a mass stove builder in Israel, emailed me asking for a phone conversation because he had some questions. During that conversation I also told him about my plans and his reaction was: why don't you make the exit of the core on the other side? Normally (with this core) the exit is in the same wall as the normal venturi port, he suggested to make it in the opposite wall. This was a nice idea, but of course not tested and I didn't know if it would work or not at all.

During construction the bench was built first and the core on the left side next to it, almost independently of the bench. When the core was next in line I decided then and there that Adiel's idea would be built, we still had some time to rebuild it if it really went completely wrong.



The bench is completely hollow, there are only three columns in it to support the seat. The exit is where the pipe comes up, the opening is right at the bottom and overly wide to give the gases room to round the bend. There is also a bypass provided, it is a T-piece that is incorporated in the pipe where the valve is housed. Out of sight, unfortunately.



Anyone who has followed the development of the Shorty knows that the lining in the riser is fitted on three sides. Left and right, and a double one around the port. Here it is different, the whole lining is turned 180 degrees, mainly in order to keep the double vortex a bit further away from the exit.



Above the gate the lining stops and the riser becomes wider, to give the gases the opportunity to expand.



Here it is a bit clearer how the core relates to the bench, in fact the core blows the gases into the backrest, which is therefore quite spaciously.



Here it is complete, the red bricks on top of the backrest are there to see if the extra mass would provide longer heat storage. In fact it didn't do much.



After the first attempts to keep the fire going we finally managed to dry the thing in about four hours. The next day someone brought a piece of ceramic glass for on top of the riser, so that everyone could see what was happening inside. The whole thing worked perfectly, completely smokeless even during refilling, nothing to smell, heat distribution over the bench very homogeneous in horizontal direction. The seat as a whole remained somewhat cooler, the backrest could have much more mass.



It was surprisingly pleasant to sit on the bench, the opportunity was therefore used extensively. The man on the bench is Oliver Kreuser, my co-builder in this project.



Later in the evening of May 17th, the glass on the riser really came into its own, here is a short video of what was visible.

https://pberg0.home.xs4all.nl/pictures/dev2025/benchrocket/MOVIE.mp4

All in all a very successful workshop, I came home very tired but very satisfied. For those who are interested in the actual construction, here is the drawing in SketchUp 17 format.

Unfortunately, my hair hasn't been dark brown for a long time anymore, there's not much left of it either and I often wear a cap... The man you see in the former picture on the back is Patrick, one of the other participants, and less than half my age. There aren't many photos or videos of me around, I usually keep a bit of distance when smartphones are being waved around. Here's a photo of me taken by yet another participant.



In case this one picture doesn't give you much to go on: together with Stefan Polatschek, a participant who is only 8 years and 9 days younger than myself, we have been doing a few pictures every year since 2023 á la the Grumpy Muppets, known as Waldorf and Statler, the two old men who kept making comments while sitting on a balcony in the Muppet show. The one on the right (left for the viewer) is Stefan.

Excellent build Peter
The Shorty design is proving highly adaptable to changes.
Even changing the riser arrangement, she still performed just as well as the original design.  
Quite impressive, Sir!
You have created another masterpiece!

Thanks for the compliments, Thomas.
This is another one to place in a nice frame and hang it opposite my bed so I'll see it in the morning.

Banter aside, this workshop was nothing short of a gamble. There were multiple first applications in there, the modified core being not the least of it all. The fact that it turned out so surprisingly well, also to me, is a good sign that the Shorty design is a sound one.

I am mighty pleased with it, honestly!

Great build, Peter! Expands the proven configuration possibilities significantly. I was very interested to see that you were able to have the exit port opposite the firebox port (with appropriate lower liner alterations). I had asked you about such a configuration in a straight/normal alignment, and you said it had been tried and failed. Do you think the liner arrangement here made the difference, and would it work with this liner arrangement in a straight alignment as well?

Glenn Herbert wrote:Great build, Peter! Expands the proven configuration possibilities significantly. I was very interested to see that you were able to have the exit port opposite the firebox port (with appropriate lower liner alterations). I had asked you about such a configuration in a straight/normal alignment, and you said it had been tried and failed. Do you think the liner arrangement here made the difference, and would it work with this liner arrangement in a straight alignment as well?

Hi Glenn,
What we tried last year, during the AFPMA gathering, was to have the exit vent to the side of the riser. It happened to be a straight core, and we fiddled a bit with the liner configuration, to no avail. The two guys who were helping me were the chair man of the Masonry Heater Association and the vice-president of the MHA's technical committee. These guys, both mass heater builders, knew what they were doing, but this core is too easily to configurate out of balance. It was a learning experience, that's where experiments are for, don't you think?
Based on that experience, I tried to reason why it didn't work at the time, so I tried another approach which, to my knowledge, might be a better approach.

Now, to answer your question directly: in a straight core, the exit opening could be at the back of the riser instead of at the front. Provided the liner is changed accordingly, of course. If you want it to vent to the side, it would be best to use a sidewinder setup. When coupling to a bell or bench is the goal, the Montendre experiment is the way to go, let's call that one a reversed sidewinder?

So the overall configuration can be straight or sidewinder, but the riser box needs to be either original (exit port above firebox port) or reversed (exit port opposite firebox port). This gives a lot of potential combinations for different installation situations.