adama
New Member
Posts: 4
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Post by adama on Aug 27, 2020 13:52:02 GMT -8
We have been asked to build a double-bell batchrocket mass heater to provide heating on two floors of a house: living room downstairs and bedroom upstairs. We haven’t made one before, so here’s my first pass at a design. I’m inviting you all to provide feedback. The heater is a 180mm system, which I believe is enough to heat both spaces - they’re each about 65 cubic metres. Due to the layout of the house the bells are not vertically aligned. They’re connected by insulated, double-wall flue pipe. The horizontal distance between the bells is 1.1m, with 2m vertical rise in the connecting pipe. The requirement is for as close as possible to an equal heat output from the two bells. To try to achieve that I’ve done the following: - Raised the outlet of the lower bell to nearly half a metre above floor level to reduce the effective ISA to about 3.5m².
- Built most of that bell with a double skin of brick with Superwool insulation between the skins.
- Made the ceiling of the bell with a double layer of bricks with Superwool between.
- Insulated the firebox with Superwool.
The upper bell has single brick walls and a double-layer ceiling like the lower bell. It has an ISA of 3m². The final fluepipe is at least 3m tall. Enough to ensure a good draw? The image here is a section through the two bells: photos.app.goo.gl/rQ9GGyCTauHQoxb57The core is built to the specifications developed by Peter (and others) and described on the batchrocket.eu site. We have built heaters with system sizes of 100, 125 & 150mm so far - all with good results.
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dcp
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Post by dcp on Aug 27, 2020 21:41:19 GMT -8
questions : 1. does it have a bypass for cold start??could not see om drawings... 2. Could be better chimney connection on first bell with bypass and on topp floor conection at chimney after the sistem is hot?? Just thinking..
another thought: If the chimney is in the middle between the 2 bells it will be higher for cold start on lower bell (wich is a pozitiv feature) and easier to conect the second bell at topp floor. also the levers for opening and closing passage of the gases could be easier to handle from the bottom level. All in the same vertical pipe...
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Post by peterberg on Aug 28, 2020 11:53:36 GMT -8
Hi Adam, welcome to the boards. I understand you deliberately underspec'd the bells which is a good thing in a double bell system. The short chimney stack is not helping much, as it is you could expect trouble while starting up from cold. Using this setup, the first bell will be inevitably warmer than the second.
May I suggest the following amendment: two exits in the lower bell, one low as usual using an elbow or T and the other significanctly higher up but still well below riser top end. That second exit done using a T-piece with a closing valve in it, the T on its side like the bottom one in your drawing. And the (then) horizontal with the valve in it, so in open position the valve would work as a bypass. I think dcp is pointing in the same direction but there's only one valve necessary in this case.
Overall, it opens the possibility to warm the top bell earlier without a fixed distribution pattern. The bells could be somewhat bigger then also. Since the goal is to have the same yield from both bells I'd recommend to have the same weight in both. And preferably, but this might not be possible, the same size.
It might be that in daily use the bypass would be open just a bit, exiting part of the hottest gases to the second bell all the time.
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fuegos
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not out of the woods yet
Posts: 177
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Post by fuegos on Aug 29, 2020 2:05:49 GMT -8
Forgive my ignorance as a beginner but wouldn't a single bell with a hot water system for a radiator be a simpler solution ? I would be interested to know how insulated flue pipe performs in a RMH set up.As for the final flue pipe i assume the 3M includes exit through the roof ? We had the same set up on our box stove & adding another 1 M -33% more - helped significantly with draw.Having at least 1M above the ridge on a pitched roof can also help in windy conditions. But simple & safe doesn't make progress ! so good luck , i'm looking forward to seeing the results .
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adama
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Post by adama on Oct 15, 2020 2:14:11 GMT -8
Hello again. Thank you for the helpful responses to my post. And apologies for the very slow reply. We’ve been very busy these last few weeks having built 4 rocket mass heaters in different parts of the country. We will start building the double bell heater very shortly. I’ve made some changes to the intermediate flue to incorporate the bypass/regulator. Here’s the revised layout: photos.app.goo.gl/zKNPGRAy3tbT4Kqa8The ‘cool’ outlet from the lower bell is roughly the same height as before, though now it sits on a brick-built extension to the back of the bell. The top of the bypass (hot) outlet is 180mm below the riser top. The final flue will be at least 1 metre taller than my first estimate, so 4m minimum, which as fuegos said should improve the draw in the system. peterberg You mentioned that ideally the two bells would have the same size. What is the reasoning for that? Thanks again for the feedback. I’ll post pictures of the build as it happens…
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adama
New Member
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Post by adama on Oct 15, 2020 2:19:33 GMT -8
Forgive my ignorance as a beginner but wouldn't a single bell with a hot water system for a radiator be a simpler solution ? I would be interested to know how insulated flue pipe performs in a RMH set up.As for the final flue pipe i assume the 3M includes exit through the roof ? We had the same set up on our box stove & adding another 1 M -33% more - helped significantly with draw.Having at least 1M above the ridge on a pitched roof can also help in windy conditions. But simple & safe doesn't make progress ! so good luck , i'm looking forward to seeing the results . I hadn't thought of using a radiator instead of a masonry upper bell. Intriguing. With the right layout and big enough pipe a simple open, gravity fed system, i.e. safe, could be made fairly easily. How to size the radiator though? And how to regulate its temperature? We're often asked about the possibility of water heating with our stoves. So far we haven't developed any solutions. Would need some experimentation...
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Oct 15, 2020 3:05:09 GMT -8
The problem with running a direct system for radiators is corrosion .Years ago we had a Rayburn with a back boiler that had an overflow/expansion pipe that emptied into the cold water tank.The one radiator we had eventually rusted through .Once or twice when i got carried away with loading up the firebox & burning hard the water started to boil & i had to open the hot taps to bleed off the water.Maybe the way round this is an open system with an indirect hot water cylinder ? i think you can find an online calculator to size the rads - if you know how many BTUs the core will give.The Rayburn had a back boiler , a rectangular tank behind the firebrick . Mathew Walker has made a version of his riserless core as a water heater , check out his Youtube .One thing that Matt points out is the ability of water to transfer heat so placement and size of the boiler is critical.i think i have seen a build on here that uses the core to heat rads ?
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Post by peterberg on Oct 15, 2020 12:51:05 GMT -8
peterberg You mentioned that ideally the two bells would have the same size. What is the reasoning for that? I seem to recall you said both bells should be about the same heating capacity. Those should be the same size and mass to achieve such a goal.
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Post by floris on Oct 29, 2020 15:38:46 GMT -8
We will be building this heater in the next day or 6. If you'd like to follow the process you can do so on Thanks all for your help, especially peterberg. If you would like to see the design, send me an email at info@batchrocket.eu and ill send you the sketchup file.
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