Julian Adam

I would like to add to Glenn; if you are using the buildup with insulation under the slab, if you have the option, it's best to use XPS or EPS. Especially XPS does not suffer from moisture, PUR (nowadays the standard insulation, at least here in the EU) does. I will be using XPS for my underfloor heating (backup/alternative to my RMH).

Matthias, if I may quote Peter, a bit higher up in this thread:

Peter van den Berg wrote: The DSR3 is a nice one, very spectacular to see it burn. Although complicated to build, some materials aren't available everywhere. But it is as self-regulating as a Shorty core which development followed logically after this one.

I read self-regulating as you don't have to do any fiddling with the air intake - it 'decides' itself to dampen the air intake. As I understand, most people don't touch the air intake on batchrockets, probably just loosing a few percents in efficiency. But you can hear what Peter has to say on the matter.

Scott Weinberg wrote:
Being that I built into my  7" sized bell with related ISA  measurements, a very simple 8" dia inspection door that takes all of 10 seconds to slip off and inspect the insides, I found exactly as Peter mentioned.

Thanks for adding your experiences to this thread Scott!

Peter, I've started my build a few months back: https://permies.com/t/261401/BBR-inch-mm-sidewinder-build
Unfortunately I don't have enough free time to continue building as quickly as I'd like, giving too much time for thinking...
With 'my original question to you' I meant in my build thread, I asked about the 5 times CSA clearance around the core, and after your input I increased the clearance to around 7.5. The external skin is built now. Using the shorty core instead of the original batch box, I would be sacrificing some of that clearance again due to the deeper port, to around 6.1 times riser CSA. My sketch was not sufficiently clear.

Forgive me for sharing my thoughts:
If I'm using the shorty core, I could keep the door in the middle, but there will be a 'slit' to the right of the core which I probably shouldn't count as clearance around the core. Plus the hot gas would directly be aimed at my chimney.

Other option is to put the door at the right side of the bell, then I would be able to use the ful 6.11 x CSA clearance. Only concern would be 'side gap' (eq. to top gap for shorty) of around 20 (assuming some extra mass / insulation where the gas hits the bell's wall) - 24 cm, which is less than the recommended 2 x system size.

Peter van den Berg wrote: Most of the time there are three steps:  door open a crack to start with, door open half a crack (step1), door closed (step2), partially close the air inlet (step 3). With half a load step 3 is left out, the exhaust temperature will be stable by itself in that case. Time isn't the factor to go by, always the exhaust temperature. This a result of testing this heater endlessly, there seemed to be a direct correlation between chimney temp on the one hand and performance in terms of highest efficiency and lowest CO level on the other.

Great explanation, if I understand correctly the temperature at which to perform step 3 will be dependent on the construction of the heater / bell.

Peter van den Berg wrote: No problems with the sidewinder Shorty core, it runs beautifully. I tested it last July during a workshop and it performed just the same as a straight one. A couple of guys tried to overload the thing for hours on end and they didn't succeed, not even with a reload right in front of the port. It was a strange sight while I walked to the workshop site, saw nothing leaving the bare chimney pipe only to be met with a heater that housed a huge, roaring fire. Such moments, I became unresistable giggly and felt very, very satisfied. No wonder, its development took the best part of a year, after all.

I can imagine, at these times, it probably almost feels like you are defying the laws of nature! I must come back to my original question to you, Peter. That is, do you think the shorty sidewinder could be incorporated in my bell? My concern being that the flue gas flow coming from the riser may obstruct the downwards stratifying layers in the bell?

Peter van den Berg wrote: 2 to 5 degrees C, nothing much to speak of.

This is indeed very little, thank you for clarifying.

Peter van den Berg wrote: A complicating factor is the fact that I am used to tuning the heater down with the air inlet during the burn, in order to keep the exhaust temperature below 120 ºC (248 ºF). Between 100 and 110 ºC (212 and 230 ºF), while the roar is unaffected is very close to ideal. This is one of the things I tried very hard to have it built-in with the Shorty core, it is meant to regulate itself, independent of the air supply. That's why the Shorty is a casual burner, burning clean with a high overload resistance and good hot refueling characteristics.

I have two additional questions, sorry! :)
1. If you say you tune down the air inlet, how often do you have to play with it? Is it just closing to x percent after x time once?
2. I can see the advantages of the shorty core. My bell will be high but the shortness appeals to me because if the regular sidewinder core would ever need replacing I would be up for a (huge) rebuild, because of the tall riser. Only recently I discovered that you had mentioned the build of a sidewinder shorty version as well. I was wondering if you tested this version with your Testo? I would assume the lack of floor channel may make the sidewinder less ideal?

Scott Weinberg wrote:
I got behind on my replies, sorry.  

Please don't apologize, there is no need!

Scott Weinberg wrote:
Julian, I presume the gap difference would happen because you want to keep the face of the bricks on the outside flush with each other?  And rightly so, And I think Glen said it well, that things might not be quite as uniform, but... will you be able to really tell?  That is always the question.

You are completely right, I want to keep the outside flush. You are also right that it probably does not matter a great deal, but I'm a bit perfectionist so I like to exclude as much (big) mistakes as possible, knowing full well that once built, changes to my heater will be very hard as it will be in my living room and I have a girlfriend to keep happy..

Glenn, I would definitely be interested in these pictures! I suppose the walls looked similar to the video Hof shared? Thank you for your extra info, scooping out the ashes after a few years it is!

Thank you for the extended explanation Peter and for sharing your own experience with the red heater!

Peter van den Berg wrote: So most ash falls down, some will stay and forms the base for a new layer of soot that'll turn into ash, and so on. This layer will be insulative but is quite thin. The higher the temperature difference between combustion gases and the bell walls, the less insulative it is. Insulation isn't blocking the heat, it slows it down.

Out of interest, could you elaborate on this insulating effect Peter, e.g. what kind of rise in the flue gas temperature are we speaking of, clean compared to fouled (= e.g. after 2 years).

Peter van den Berg wrote: Last fall I modified the top of the bell, a small extension and another way to close the top. The closing method was very similar to the Mallorca build, back in 2017.

After considering building the top of my bell with an arch to avoid the superwool, for which Scott kindly offered to help (!), It looks like I will also be using this closing method. I got some second hand 9 x 9, 0.9 cm thick steel lintels which were used in a window opening. Also out of curiosity, did you build the extension to get your ISA up and flue gas temperature down slightly, I seem to recall you had around 120 °C exit T?

Peter van den Berg wrote:
This winter it's ten years ago that my red bell heater was built. Year after year, our fuel consumption was around 1.5 m3 of soft coniferous species, which equals 0.4 cords in imperial terms. In ten years, that would mean 4 cords or 6 m3, so I could expect to clean the floor of my bell when that amount is reached again. For other heaters: of course depending on the heater's size, it's construction, how high the exhaust opening is above the floor and whether or not the core is elevated. When you have lots of space down there, the interval could be anything between 2 and 10 years.

To answer the question directly: no need to clean the walls of a bell. That ash layer will fall down automatically, gravity will take care of that.

Great to know Peter! One more thing not to worry about :)

Thank you for your input Glenn, in the added picture the 'void' in the middle will have an exterior skin with the slighly wider bricks, leaving about a brick wide on both sides which would have the bigger gap. I will see if I can break the convection on a few places by making a small ridge with lime mortar/plaster.